08-19-09: I've struggled for a long time to understand solid-state - I mean, REALLY understand...
Here's an article about LEDs, but the explanation of how the semiconductor crystal lattices interact in quantum wells finally turned on the light-bulb in my head (sorry about the pun):
http://www.spectrum.ieee.org/semiconductors/optoelectronics/the-leds-dark-secret/1
>08-19-09: Wow!! My head is spinning so much has changed so fast in three short weeks...now it looks like I'm going to Nebraska again (or maybe Oklahoma or Iowa)....I just finally threw in the towel on trying to make a living in crazy AZ in my profession, and realized I had to get to the midwest where my experience is appreciated. So, my bench remains packed up in boxes, and it will be at least another month before I can unpack and set up again, and finally post on the Heathkit amps and the other projects.
Now, back to messing about with tube electronics!!!
My projects now, to be posted here, are:
1. High-Voltage (I'm not kidding) Triode Direct/Coupled Electrostatic Amplifier and Speaker. Oh, yeah!!! NO output transformer (eek! ack!) - the triode plate connected directly to the electrostatic speaker heh heh heh ;) I'm working on the power supply right now (20 Kilovolts...heh heh heh), and will be posting both the failures and successes soon.
2. Very serious and comprehensive mods to the classic Heathkit AA-151 tube amp. Purists be warned: cover your eyes if you don't like complete and total upgrading of an amp...
(It only took a year and a half and I had to disappoint a whole bunch of people...but between using Allen Wright's single-ended design for the phono preamp section, getting rid of the global negative feedback, getting rid of an entirely unnecessary amp stage in the old Williamson design, doubling up the output EL-84's for much more power with less distortion and far better damping factor, and moving the power supply back outside of the amp (which enables doubling the output tubes), I think I've finally got the final design. No more remote control; that turned into just far too much hassle and expense and complexity...maybe someday.When I get my bench set back up, and as I complete each of the half-dozen AA-151's I still have half-completed, I'll check to see if any of the original orderers want theirs (finally!), and, if not, put them on here for sale. As well as post all the mods, of course.
3. Homebrew General Coverage Ham and Shortwave Receiver, all tube. This is a REALLY FAR-INTO-THE-FUTURE project, don't hold your breath, but it will be fine...someday
(I will be posting soon, though, on some interesting experiments with different ways of making variable inductors and capacitors that I've not seen in classic (or modern) designs...
4. And, yeah, I'm still chipping away at bringing SENSE AND ORDER to the list of links on the right...oh, well, like I said before, perfection takes...time
Tip for the Day
(now you don't have to send in your $10 to the guy who ripped off "the mom who discovered the secret to whitening teeth"): to whiten teeth, mix a strawberry with 1/2 teaspoon baking soda: if you were wondering if other fruits than strawberries could be used - combined with baking soda - for whitening teeth - the answer is yes, probably: any fruit that has malic acid in it will probably work. Strawberries, are, however, a heckuvalot easier to mash up - an important consideration if you can get them easily. Fruits with malic acid include: Strawberries, Green Apples, unripe apples other varieties, green grapes, probably any unripe citrus fruit, rhubarb (!) - the edible stalks, not the leaves or roots!!...and like that. Probably just about any unripe fruit would work, most fruits have SOME malic acid in them, especially when they're still unripe. Just mix a little mashed fruit with roughly the same amount of baking soda, brush onto teeth, sit 5 minutes, brush off and rinse thoroughly. If the fruit doesn't work...try another type! (Or you could just get malic acid at a wine-making store, but note caution that follows): DON'T OVERDO: any whitening process can remove enamel, and if you overdo it, you'll get really sensitive teeth, maybe damage them, so pay attention and be a little cautions, OK?6-21-09: I have started reorganizing the links on the right by listing them numerically. It's the only way, with this blogware, I can keep them in order...
I'm putting them into categories. It's a WORK IN PROGRESS ;) - I work on this a little bit almost every day:
01. through 20.
The TOP 20 information articles or sites for tube amp DIY'ers...nothing for sale here, just MUST-READ, CLASSIC or CUTTING-EDGE info. (Yeah, there's more than twenty...:)
(For sites with stuff for sale, if they don't have a separate section for tech info, they don't get listed here; look in the 20's for the "for sale" pages of the same site): 21. through 40.
The next-to-top 20 sites/pages - or the commercial side of site with great tech pages - that I find most useful for various pieces of information, projects or products. So far, all of these are MUST READS for anyone just getting into tubes, to get the best information without the baloney (no ebarf scam artists here, as far as I know....:) 41. through 60.
The best places I know of to GET PARTS TO MAKE STUFF - parts/tubes/mosfets/etc. All of these are commercial, and all are places I go to for parts frequently. It's odd, but I - and lots of other DIY'ers, I'm sure - have found that you just can't get all the right parts for a particular project from one place, even places as huge as digikey. And, even though you can buy a little cheaper (in quantity) from massive warehouses like digikey and mouser, etc., the personal service and wealth of info at places like Angela, Antique and Triode Electronics is well worth the extra pennies. IF I LEFT SOMETHING OUT, PLEASE LET ME KNOW, I DON'T MEAN TO LEAVE OUT ANY LINK TO A DECENT SITE. The more the merrier.
61. through 70.
To Be Determined...(I forget) 71. through 80.
Places to GET VACUUM TUBES (some of it repeats from 21-40; most of them sites devoted to vacuum tubes primarily, including places world-wide for Russian, rare British, Australian, etc., vacuum tubes.
71's: Sites for vacuum tubes, that cover just about everything;
76's: Sites for Direct Heated Triodes (U.S./Canada/Australia/England); 77's: Sites for Russian or Eastern European vacuum tubes;
(more categories to come)....:)
NEW PROJECT: I am happily :) working on a direct coupled tube amp electrostatic speaker. Oh, I'm psyched about this one. No output transformer, of course (aack! eeeek!). A very high voltage triode (REALLY high voltage, no joke), with the stator driven directly from the plate. Not to worry, such high resistance that it couldn't even kill your cat...although the dog will definitely think twice about ever peeing on your speakers again....heh heh heh :)
So, it's a huge electrostatic speaker, with it's own tube amp built into the base and direct coupled to the electrostatic speaker, no transformer. Then a line amp is in the center, with a cable to each tube amp/electrostatic speaker combo. CD's, phono's, radio, internet, TV, go into the center line amp.
The center line amp will be anything you want to use, doesn't much matter. I am also in process with a center line amp that is remote controlled and has a zillion tone controls (bass, low-mids, high-mids, treble, pentode/UL/triode, variable global negative feedback, etc.), but the tube amp/electrostatic speaker combo comes first.
P.S.: I recently found Alibris, which has cheap copies of Robert Tomer's book from 1960, "Getting the Most Out of Vacuum Tubes"...it's linked on the right, but here's the link again...go there, buy it, read it. http://www.alibris.com/booksearch?binding=&mtype=&keyword=getting+the+most+out+of+vacuum+tubes&hs.x=0&hs.y=0&hs=SubmitKeep in mind that this book was written by an engineer who collected vast amounts of data from industries that used even vaster numbers of vacuum tubes in industrial equipment, including audio and RF, that cost big money to service and repair when something broke down...so, his information may be from 1960, but it's scientific, it's specific, it's sensible, and it's based on the best tubes ever made by giants such as RCA and GE. So, if you REALLY want to know how to design in order to protect tubes and give them the longest life possible, buy this book, read it, and follow the principles. And ignore the dunderheads who, because it's convenient, and who have never REALLY done the necessary science, tell you that you don't REALLY have to delay B+ before the filaments are hot, or that preventing filament turn-on surge REALLY doesn't matter, or the rest of the long list of baloney people try to tell you just because they're too lazy or too cheap to do it right. If I just pissed someone off, good. They need to wake up.
On the other hand, if you don't believe me, by all means, knock yourself out, forget the delay and the surge protection....far be it from me to try to tell the world how to do whatever the heck it wants to do (as one gets older, one sees the futility of trying to change belief systems...)
I'll write an article on this soon, including EASY ways to delay B+ and prevent filament turn-on surge, but for now I'll leave you with one final little shocker: Tomer presents scientific data that demonstrated that tube testers do nothing but greatly increase the rate of early tube failure!!
He documented that in many tube testers, the transconductance of the tube was significantly reduced during the first test and the lifespan was shortened. Industries that had maintenance programs that pulled tubes for testing on a regular basis had a far higher premature failure rate than if they left the tubes in place and monitored circuit parameters. Interesting, huh?
So, buy your tubes NOS from Antique or another good supplier, and forget those "tested" tubes on ebarf (if you really want to save an old NOS, the first time you fire it up, just heat the filament for half an hour to several hours...no B+. THEN add B+ very slowly. After that, it should be fine. The idea is to get the getter activated, clear out any vapors that might have formed, and burn off any dust or debris that might be hanging in there. Throwing a 60 year old NOS into a tube tester that hasn't been heated up since it left the factory and hitting the test button is a great way to destroy it FOREVER....just a word to the wise ;)
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I guess I'll have to take back what I said about wigix - it may be a good alternative to ebarf for mass-produced commodities - but it's not going to help tube amp DIY'ers a bit. Just on a lark, I asked to be permitted to be a Sub-category expert for tube amps - not because I'm an expert, there are hundreds of guys far more expert than me - but just to see what would happen...plus I would have done my very best to include every tube amp, past and now...but I just got the brush-off. Wigix told me that tube amps were "Vintage" products, and that Wigix doesn't DO "Vintage"...so I guess I'm not going to DO Wigix!!!!!
I guess we're just pretty much stuck with ebarf.....EXCEPT......
There is a site that both sells tube amps and has an auction section for amps and audio equipment:
http://www.audiogon.com/
Most of the stuff on audiogon is waaaaaaaay too expensive for me...but I did see some stuff at quite reasonable prices, along with some interesting auctions, so I would recommend you give them a look-see. They claim to have a huge viewer-ship, so maybe it will become the tube DIY'er's alternative to ebarf.
NOTE: I'm still finishing up the amps I started modding Lo, These Many Months Ago...(now a year!!)...but they're close to done now, so I will be adding new articles, and finishing some of the ones I half-wrote, sometime....... Yeah, I know, a year seems incredible...but wait till you see them. Every time I thought I had the design finalized, I realized there was onnnnnnnnnnnne more tweak I could add, and it kinda...got out of hand. But it really (no, really!) is done now, and the first amp is about to ship, the rest in line right after, and THEN I can post all the yummy pictures. The pictures are gonna knock your eyes out, not to mention the plans, schematics and close-ups of the CCS construction, NMOS source followers construction, etc. ("It ain't boastin' if yuh done it", unknown...if you know the source of the quotation, by all means let me know :)
I now have an HP 3581A Wave Analyzer, and a PC-based spectrum analyzer, so look forward to some realistic distortion analyses, where I'll start at the input to the amp, and show what happens to the signal each step of the way...and then we'll understand better what ends up coming out the end. It's all (well, mostly all :) about topology.
Until then, do check the links from time to time, I'm adding INCREDIBLE links all the time on the right, just SUPERB sites. The web is a truly amazing place.
We must keep the internet free!! Free to access, free to post, free to download, free of censorship (except for illegal things like exploitation of children, of course), FREE OF CORPORATE INFLUENCE, because with a free internet, all things truly are possible. I believe the internet is the next step in the development of human civilization, and holds promise for people everywhere (except places like China and - sigh - Russia right now, where the repressive governments have imposed internet censorship - but I do believe all this will change, humans will put up with censorship for only so long).
Check out the link to a truly beautiful Japanese DIY'er's site I recently added (although I still haven't been able to figure out what his name is!...if anyone reads this who reads Japanese, and can figure it out, please let me know. You CAN post now at the end of the article, it just goes through me first.....
Hi, if you're like me, you're looking for something really special in audio - with a truly open mind - and the willingness to DIY - Do It Yourself (to some extent) in order to make superb affordable.
And you like things done well just for the fun of it - there doesn't have to be a universal truth, it doesn't have to be "the only" way to do it - but it IS superbly done - and you do it for the sheer enjoyment of it.
Someone once said something like this: "You can be assured manufacturers will find the cheapest way to do things fairly well. Not the best, just the cheapest." And, unless you're rich and can afford to spend $100,000 on a pair of speakers, that's just the way it is - you can have OK and cheap, or you can have some of the best and ridiculously expensive -
or you can have superb - almost the best - and do most of it yourself.
This site is how to DIY superb audio from my own perspective. There are other sites that also show how to DIY superb audio, but from different perspectives. I'm not claiming my way is better! Just a different way of looking at it. That's why I'll have a list of great sites on the right hand side and great projects on the left side, when I get to it (right now I have to drive Cameron to his friend's house). My starting purpose may surprise you a little:
I believe in tube amps completely supported by solid state engineering. The key word here is "supported" by...nothing solid state in the signal path...except mosfet source followers, which add or take nothing...but vacuum tubes working with SS Constant Current Sources, buffered by mosfet source followers, control grids of tubes biased by op amp servo circuits that are NOT in the signal path, and outputs from vacuum tubes not through a transformer, but through a CCS'd voltage-to-current mosfet source follower converter.
But, as I've worked on this site, I've found a second purpose that, is to me, just as important: being a resource site for others, that helps you find great stuff on the web: great forums, great projects, great educational material, great vendors. So, my list of favorite links on the right side is LONG and getting longer. I find everyone of these links useful, frequently. I come to my own home page all the time just to use my own links!!
Note: all the links are listed on the right, grouped as best I can. COMING: all the same links organized into folders on the LEFT side of the page.And, there is a third purpose for this site: mods to Heathkit AA-151 amps, a place I can document ways to improve the old amps. If you have suggestions, please feel free to send them, I think I have all the comments links at the end of the articles working now...comments have to go through me. I'm easy to get along with, and I like different perspectives and ideas, so please don't be put off by the security of the link...it's just to stop spammers.So, this site is intended to be: 1. a resource full of links to great tube amp sites and great "audio" sites on the web world-wide, 2. a resource for showing ways of making tube amps that use SS engineering, and 3. it's intended to document a whole mountain of cool mods to the venerable, sweet-sounding old Heathkit AA-151 - improving it without losing it's inherent sweet tone (mostly due to the combination of it's output EL-84's in UL PP and very good output transformers) - as well as, later, the AA-100 (which is a pentode PP higher power amp but not sweet-sounding at all....so, PEOPLE, please stop bidding these things up on ebarf! They're not that good - actually, pretty bad - without serious modding!).
And, except for modding old tube amps - mostly the Heathkits - primarily the AA-151 and, later, the AA-100 - this site is also going to be dedicated to something that is even more heretical than using SS to support tubes: we're going to get rid of the output transformer altogether.
Which doesn't mean I'm against tube amps with output transformers...far from it. It's just that there are already so many GREAT tube amps with ouput transformers, including the old McIntosh MC-30, probably the greatest of all time, but also including more modern tube amps with output transformers, such as the ones on Max's AngelFire site (see links on right), there's just no point in me adding more. What I WILL do is include lots of links to great sites for traditional tube amps (traditional in the sense of using output transformers), including the kits at Antique, Angela and Triode, to name just a few. Actually, now that I think about it, I am going to eventually do a mod for the old AA-151's and AA-100's that will get rid of the output transformers (even though they're quite good ones)...heh heh heh
...and which will transform them (heh, get it? transform?) from 14 watts per channel to .... oh .... hundreds of watts per channel....or pretty much as many watts as you want. Want a thousand watts per channel?....this can be done heh heh heh.... So, the name of this website is kind of an "inside joke" - this site is mostly about building tube amps without output transformers - by using a different method to transform voltage to current - which is what you have to do somehow in order to drive speakers.
I had a revelation about this recently after years of modding old tube amps and reading articles about various new designs - I realized that all of these designs had one problem in common - how expensive - or less than perfect if cheap - output transformers are, and how you have to spend a lot of money on a really big one to get really, really good audio, and how much engineering you have to do to make the amp work well with the transformer, even if it's a great one.
I think some people, who have an engineering nature, like the challenge of how to get around the disadvantages of an output transformer. I also think that many DIY'ers find that particular part of amp design the most difficult....it's just an observation I've made over the years, that how to handle choosing the impedance ratio and how to use global feedback and how to design Zobel networks and how to get good bass without spending a fortune or losing the treble, and then on top of that how to figure out which transformer to buy and how much to spend...it just all becomes very difficult.
Now, McIntosh figured out how to solve the output transformer problem years ago, by using "four-build" (four layers of insulation) magnet wire, adding a cathode feedback winding that was wound alongside the plate windings (each wire side-by-side, this was serious stuff), and using that cathode feedback as essentially 100% local feedback, so that there was no transformer distortion to bother measuring. If you get ahold of an old MC-30, and know how to fix it up, by all means do so. But please don't drive the prices up any higher than they already are...despite it's perfection, it's still an old tube amp that needs complete recapping...at the least.
Now, if I were to become a DIY OPT-winder-master, I'd just copy the McIntosh method, except maybe add a separate screen winding for UL at a lower bias point...and I admit I keep being tempted...
...but the same problem that McIntosh had still exists: core materials, such as M-6 lams (laminations), are far from perfect...and must be bought in bulk (translation: train-car loads)...to be economical for the DIY'er...and better core materials cost a FORTUNE!...and magnet wire with truly high-voltage insulation CAN be had, but not cheap. No, I don't mean those magnet wire coils sold on surplus sites or sites that specialize in small parts. Wind up a McCintosh OPT design with that stuff, and be prepared for fireworks! It really is NOT SAFE to put plate windings and cathode windings side-by-side unless you have really, really good magnet wire and know how to do it right, so.....fogeddaboudit.Criminey, now I really WANT to DIY a true Mac OPT, but add the screen winding, just to show off....but I'll do my best to STIFLE the impulse...
It's no accident that a lot of forums spend a lot of time on figuring out how to make a tube amp sound half-way decent using the cheaper of the Hammond and Edcor and Triad output transformers - most of us tube DIY'ers are broke! We can't afford good iron! If we could afford really good iron, heck, we'd just buy a great amp and be done with it! (Except for the few rich hobbiests who do this out of curiosity...let me know if you know who they are....:)
So, if you didn't know before, I'll just let you know briefly that output transformers do have faults, and that in my opinion the task of compensating for those faults sometimes does more harm than good, and you still have all that weight and expense.
Just the main problems: distortion (from the inherent hysteresis loop of the core), phase shifts (which can cause oscillations or ringing), capacitive coupling between windings (decreases the treble, distorts the treble more), insufficient damping factor (which allows the speakers to control the amp instead of vice versa - like the tail wagging the dog - causing peaks and nulls in the frequency output of the speakers), and core saturation (limits the bass output, and can, in the deep bass at high power peaks, actually make the output transformer act as a short when the inductive reactance is lost! - if this happens too badly, the output tubes can be damaged and the output transformer can actually be burnt out.)
What is the main strategy used to minimize the distortion of the output transformer? Global negative feedback. What does this do? Loses musical content, subtle musical information. We've known for a good forty years now how to make an amplifier have virtually zero distortion...but that doesn't mean the amp sounds good. In fact, many of us find music through an amp with low distortion, due to a lot of negative feedback, to be lifeless, dead, dull.
How is the problem of phase shift causing oscillation dealt with? Limiting bandwidth. RC damping networks, which are as much magic as math (the math will get you half-way there, and then you have to "cut-and-try" until it works.) Hams and electronic engineers are all over RC damping networks, that's just play for them, but for the rest of us...ehh...you have to do a lot of messing about, and maybe you get it really nice, maybe you don't.
How is the problem of impedance peaks and dips from the speakers compensated for by the amp? Usually, not at all. Hope for the best. Buy different speakers. In truth, most of the time this is not a big issue. But it can be, especially when lower impedance ratios are used to get more power, or if you happen to accidentally get the wrong speakers for the transformers in your amp.
Finally, how is the problem of core saturation dealt with? Usually, by limiting how low the amp can go...or by spending a lot more money for a lot more core....which also means a lot more copper...which means, as the price of copper continues to go up, prices going ever higher.
Now, does all this matter very much with a guitar amp? No, not usually. Heck, the distortion sounds great, and some saturation just adds to the "soul-fullness" of the guitarists sytle.
Does it matter listening to classical, jazz, rock? Heck yeah, you only have to hear a great system once to never be satisfied with the cheap one you have.
So, when I personally look at the biggest obstacle to getting great sound out of a DIY amp without spending a ton of dough, the most obvious component to me is the output transformer. I saw this plain as day on a tube forum just this week: a newbie joins, after getting hold of some tubes, and wants help finding a design to build. He gets some great suggestions, but quickly runs into the main roadblock: the cost of the output iron. After rejecting, as far as I could tell, all the suggestions as costing too much for the output transformers, we don't hear from him again. I can feel his pain. There are PLENTY of great amp designs on the web...but most of them have one thing in common: be prepared to spend at least several hundred dollars for the output iron, in some cases many hundreds more.
I did spend the better part of last year sourcing lams and bobbins and frames and reasonably priced magnet wire to start winding my own, and got some help from one of best DIY output transformer makers in the world - and then gave up. You know why? Because there's a certain amount of "magic" in designing and winding a really good transformer. The guys that make them know this, and they don't keep it a secret either. When someone says they'll just wind one themselves, the custom winders just laugh and say, "Good Luck!" So, I decided life wasn't long enough - at least I don't have enough life left! - to become an expert in transformer winding - remember, the only way to find out if a particular design tweak works is to wind the entire things up and try it! And did you ever try UNwinding the wire so maybe you could use it again? Hah! Hah hah heeeh hah hoooo...no, fogeddaboutit, that's copper down the drain. So, buying iron: the cost of good output iron really does discourage me from building new amp designs....and I really don't feel like putting tons of time and effort into how to make a cheap OPT sound half-decent. So, enough! No more output iron for me.
However, we now have a way of getting rid of the output transformer
, but still use tubes for the voltage amplification part of the amp. Mosfets. So, in the amp designs that I will be posting, the function of transforming the voltage amplification that has happened inside the tubes will be handled, not by a transformer, but by a mosfet. This opens up some very interesting options indeed. Such as immense power without having to use a zillion output tubes or scary high-voltage plate supplies (like a kilovolt or more...the 813 really ought to be run at 2 kilovolts, and I am considering it, because such an amp with a mosfet voltage-to-current output would be literally impossible to clip - you'd turn your speakers into flaming infernos first (which is a problem, I admit)). Now, you can have a hundred watt amp easy, and instead of spending several hundred bucks per channel on output transformers to handle all that power, you only have to spend twenty or thirty bucks per channel - but it's still a tube amp. 
For a thousand watts per channel you'll have to spend a hundred bucks per channel on mosfets, but you can't even get output transformers for such an amp - maybe from Sowter, who can probably make just about anything, given enough money - but your only other choice would be to put ten of the biggest Hammonds in parallel. Which would be nuts. 
I also have become a firm believer in bi-amping or even tri-amping, even though I do believe in most cases bi-amping is quite sufficient. Actually, bi-amping or tri-amping is probably only need if you're using a tube amp with an output transformer - to get the bass out of the transformer, where it sucks all the energy from the amp - but it can make sense with a mosfet output amp also, allowing you to use smaller mosfets for the higher frequencies, where the gate capacitance has more effect, and huge mosfets for the bass, where the gate capacitance's effect on slew rate doesn't matter, AND getting rid of the crossover in the speaker between the mid and the bass, which is A: worse (phase shift like crazy) and B: usually made of the cheapest components possible.
A little detour (this will eventually be a category by itself): the reason I have fallen in love with bi-amping especially for tube amps with output transformers is simple: a tube amp (with OPT) can only handle midrange and treble superbly. It has a hard time with the deep bass. Unless you spend enormous money on really heavy (and I do mean heavy) output transformers...or use tons of negative feedback (ugh...a little is fine, a lot is...NOT), any tube amp that must use an output transformer to couple the tubes to the speakers will have floppy bass, especially the deep bass. Put an oscilloscope across the output, and feed square waves and you'll see what I mean: from about 300 Hz down, it's progressively distorted - in fact, a transformer cannot transmit DC. 20 Hz is really close to DC.
If you put direct current into the input of a transformer, what do you get from the output? Nothing. Think about it: audio goes up to 20 thousand Herz (cycles per second). At 300 Hz, you're pretty close to DC compared to 20 thousand! So, we've gotten used to floppy bass, and just accept it as part of tube amp culture, instead concentrating on how gorgeous and warm the midrange is and how clear and shimmery the treble is. But, unless you have an output transformer the size of a VW (OK, I'm exaggerating a little here
), you are NOT going to get really good bass, certainly not really good deep bass. Look at power line transformers, that have to step voltage down at 60 Hz, which is really deep bass. Those things are huge! It's not just because they have to transmit a lot of current - although they do - it's also because they have to operate at a frequency so close to DC. The cores have to be huge to not saturate. They're also super easy to design compared to an audio output transformer, because they don't have to also transform midrange and treble. See? That's why output transformers are so problematical - they have to do too much. 20 Hz to 20 KHz, without distortion and phase shift and loss at low and high ends, is just too much to ask of a transformer....thus global negative feedback, and the compromise between weight (bass) and copper (treble), and the devil's choice of cheap versus expensive versus very, very expensive. So, to me, the solution is not to ask your tube amp to make deep bass, for me there are too many compromises to achieve that, and I can't afford great output iron - and despite my macho attitude a few years ago (I don't care how heavy the ^(%^$#!! thing is) - to me, the answer is very simple: put a crossover into the amp right before the phase splitter that drives the push-pull output tubes (assuming it's push-pull, we'll talk about that in another blog) and split off the bass from 310 Hz down, so the tube amp only has to drive the speakers from about 300 Hz to 20 KHz. Now, THAT WORKS.
As for that bass output? Easy. Buy a subwoofer or woofer that has it's own SS amp (that's what transistor amps are GOOD for - subwoofers/woofers) and feed the bass to that. (Just make sure the powered subwoofer or powered woofer has a frequency range from 20 or 25 Hz up to at least 500 Hz, probably better 1 KHz - not a subwoofer that is only for the deepest bass, from like 20 to 55...some of them are for just those deepest tones). Then mess with the positioning of the speakers for the amp and the speakers for the bass, and then.....ahhhhhhh, enjoy.Before you get worried about the cost of the subwoofers: cheap ones made for cars will work fine. Yeah, you can get better, but cheap ones for cars will still work a lot better than that tube amp with it's wimpy output transformer, believe me.
One last word on this: many will say, hey, I've been listening to music all my life through a tube amp without splitting off the bass, and it sounds fine to me. There are three reasons for this. First, you're used to it. It's amazing how - if there's no good alternative at hand - the brain can adjust itself to terrible sound and enjoy it. Especially if the music is something you really like. I remember once on a long road trip, late at night, managing to tune in some distant station playing one of the great symphonies - I don't remember which one it was, but I'm sure it was either a Beethoven, Brahms Fourth, Dvorak's Ninth, or Schubert's Unfinished - the reception was terrible, full of noise, some other station in the background, there was no bass and the treble was covered by the hiss, and I still enjoyed every moment of it. So, we adjust to lousy sound. Sometimes because we have to, and do so consciously and cheerfully. Sometimes because we're become accustomed to it over a long time without anything better around. But that doesn't mean you have to spend the rest of your life missing out on great bass. It DOES make a difference - especially the frequencies between 200 and 300 Hz.
A second reason people have accepted bass through a tube amp is that the ear actually accepts a lot of distortion from the bass without protesting. If the midrange is beautiful, our brain is engineered to not miss the bass terribly. It's just part of neuroacoustics.
There is a third reason, though, that I think might surprise you. Bass speakers make a lot of second harmonic distortion. Don't worry, our ears like second harmonic (h2) just fine. When a distorted bass spike comes from the tube amp to the speaker, the speaker does such a lousy job of reproducing that awful spike that the resulting sound is actually a second-harmonic-distortion-approximation of what the bass waveform actually was! So, all in all, tube amps have gotten off easy when it comes to truly good bass response for almost a hundred years now.
But I still believe that if you ever hear a good bi-amped system, you'll be amazed at how suddenly bass is so clear, articulate, full of detail and thunderous all at the same time, not the floppy background grumble you're used to. (Note to Max: yeah, I'm probably over-exaggerating a little...)
So, when I mod an old Heathkit amp, what is one of the things I do? Install a crossover, that's what, and let your Heathkit handle the midrange and treble, and let a separate self-powered subwoofer take care of the deep bass. The same for my 6BQ6GBT amp below, and for my 813 amp below: a crossover built right into the amp, and let the bass go to separate subwoofers. Trying to make a tube amp handle everything from deep bass to high treble is like trying to shovel sand against the tide, in my opinion. By the way, the circuit for that crossover has already been done by Rod Elliot, and there's no point in you or me reinventing the wheel on this one. To make your own crossover to install at the right place inside your own amp (if your amp has a "tape loop" in and out, you can just use that), go to his website at this page (there's more than this page, but this is a good place to start):
http://sound.westhost.com/project09.htm
(the link to his home page, because he has a ton more stuff than just the crossover, is in the list of favorite links on the right side of this page near the top)
The rest of his site is highly recommended. (http://sound.westhost.com/)
Tubes only do one thing really well: they voltage-amplify an audio signal and add a "tone" or "character" to the sound that really pleases the ear. There are lots of theories as to why tubes make audio sound better, but the fact is we really don't know why tubes make audio sound better - we just know they do.
Now, mind you, something that might surprise you: Probably the most linear device in all of electronics is a (properly set up) Triode. Not a pentode, not a beam former (modified tetrode), not a mosfet...and for Heaven's sake certainly not a transistor!!! And, even when a triode is a bit over-loaded (they often are), they usually generate mostly just 2nd harmonic distortion, which our ears like just fine (nature is FULL of 2nd harmonics. As Nelson Pass...or Lynn Olson...(heck, I can't find the reference right now) pointed out, any sound in nature is comprised of pushing air and then pulling air - and since air pushes more quickly than it can be pulled, 2nd harmonic generation from any vibrating source - whether it be a hound-dog howling, a cricket chirping, the wind rushing through oak trees, or a violin playing Beethoven - is going to be the dominant pattern of distortion, so we are neurally adapted to not only not mind some 2nd harmonic, we probably think it makes sound more "natural". But, the fact remains that a properly set up triode is very, very linear, with only a tiny amount of distortion, and the tiny amount there is, is 2nd harmonic. So, an extremely well set up triode amp, even without any negative feedback at all, is capable of vanishingly low distortion! (Just so long as you don't need tons of power, another subject for another day...)
Now, Nelson Pass has recently made the statement that 3rd harmonic seems to be preferred by most people in a push-pull output circuit, over 2nd harmonic....but I'll have to write a separate article, after I do some testing, on THAT idea. He may have a point, though: the Heathkit AA-151 is a push-pull output EL-84 tube amp, and it DOES have higher 3rd harmonic than 2nd...and it DOES have a "sweet" sound...but I think something is going on between the interplay of 3rd harmonic from the amp and 2nd harmonic from the speakers where the final "waterfall" pattern is actually restored...but let's move on for now with the present argument, I'll figure out what's really going on in this 3rd vs. 2nd harmonic debate in another blog:
So, how come op amps and transistor amps have such low distortion, like ridiculous numbers like 0.001%, which seems, like, PERFECT? By using TONS and TONS of corrective negative feedback, that's how come. Which some audiophiles believe loses musical content. I'm not COMPLETELY sure about that, but I think it's certainly at least partly true...there are subtle nuances to sound that we are far from understanding yet, and if a signal is terribly distorted by the non-linearities of transistors and then the output is FORCED back into a low distortion copy (but amplified) of the original signal, it's hard to imagine that some of those subtle nuances, many of them probably down in the "noise" floor, some of them extremely brief but actually of very high amplitude, are not lost.
There is another consideration with global Negative Feedback that was missed for decades. If the amp has any coupling capacitors in it...that is, capacitors directly in the signal path...then the phenomenon of "blocking" can become a serious problem...and global Negative Feedback (gNFB) makes the Blocking far worse. This is important. What is blocking? That's when a sudden loud transient (drum, cymbal, etc.) or rapid crescendo momentarily drives the next stage into cut-off, or clipping (usually the output stage), and the coupling capacitor gets "unbiased", so to speak. A coupling capacitor driving a stage has to be biased somewhere near the "midpoint" of the stage it is driving, so the stage can swing both "up" and "down" without hitting the ceiling or the floor. The capacitor swings up and down first, and the next stage follows this swing. For the capacitor to be able to swing up and down within the range of the next stage - that is, swing up and down between ceiling and floor without hitting either - it has to be "biased" at a voltage that is near the midpoint - about halfway between ceiling and floor.
If the "far" side of the capacitor has this huge charge on it momentarily that hasn't drained off - so the bias - midpoint charge - can be restored - and a new audio signal peak hits the "near" side of the capacitor...what happens? Nothing. The capacitor, because the next stage it is connected to is still stuck to the ceiling or the floor, "blocks" the signal. The amplifier loses sound for a moment, and as the sound comes back, as bias (midpoint) is restored to the capacitor and following stage, it comes back extremely distorted. It sounds awful.
Here's why: in our analogy, we've got the next stage stuck to the ceiling or the floor. As bias is restored, as the capacitor floats back to the midpoint between the ceiling and floor, and sound starts to pass through the stage again, what happens to the WHOLE sound, the swing both up and down? One side or the other gets cut off. If the stage was stuck to the ceiling, the half of the signal that went UP is cut off. If it was stuck to the floor, the half of the signal that swung DOWN is cut off. As bias - midpoint - is restored, then more and more of the entire up and down swing of the signal is restored, and the sound gets less and less distorted.
Ever hear of a Fuzz-Box for an electric guitar? Basically, that's what is happening in the effects pedal - part of the signal, either the UP swing or the DOWN swing (or both) - is getting cut-off. Might sound great for a Heavy Metal Rock Band - and it did sound great when The Ventures used it in 1961 (2000 Pound Bee), and then Dave Davies of The Kinks imitated it by cutting razor-blade slashes in his speaker cone, and especially when Keith Richards of The Rolling Stones used a Gibson Fuzz-Box for "(I Can't Get No) Satisfaction" (referenced from wikipedia: http://en.wikipedia.org/wiki/Fuzzbox) -
...but Beethoven through a Fuzz-Box? Miles Davis through a Fuzz-Box? Maria Callas? Deborah Voigt?....
...or, to carry a joke too far...
...Ruben Studdard or Jordin Sparks through a Fuzz-Box? Well, maybe Studdard or Sparks (or Taylor Hicks - that might work!!!)...
(just kidding) 
(I actually really LIKE Taylor Hicks. The rest I could live happily without....)Now, the bias on the capacitor will be restored fairly quickly, but that "hiccup followed by a burp" in the sound of the amp still ruined a musical moment. Here's where gNFB comes back as a little devil.
Remember that gNFB forces the amp to have the same output as the input, except for amplification. Some of the output signal from the output transformer is fed back to an input stage inversely, so that any deviation from the input - at the output - is fed back from the output - to the input - as a correction. Sounds like a great idea, huh? It's how amp manufacturers, whether transistor or tube, were able to get those 0.001% THD numbers. But, here's the rub: if a high amplitude transient (sudden loud sound) goes through the amp and hits the output stage and clips the amp, the gNFB will send it back to the input stage inversely in an attempt to "unclip" the output...which can't be done!!!!! Explanation: The output is already clipped...and now the gNFB is trying to make it go louder...so it just clips longer...
So, what was before a tiny moment of Blocking now becomes this long, distorted, ugly string of moments as the amp is sent into clipping oscillation...the input is trying to correct the output clipping because of the gNFB telling it to, which just clips the output more, and then the gNFB tells the input to correct THAT, and, as you can see, the cycle repeats itself over and over until it eventually dies out from internal losses in the amp. Worst case: the amp goes into a loud, buzzing oscillation and doesn't stop until you turn it off. This usually doesn't happen, because the frequency range of the amp will be limited in order to prevent this. Usual case: a spoiled moment of crescendo where all the clarity is lost. You hear something loud, but it doesn't sound good - there's a mudiness, or background buzzing or crackling, or even a loss of sound followed by fuzziness. The first time I heard this, I thought it was my needle mistracking in the vinyl groove...until I turned down the amp volume and realized it was the amp, not the turntable cartridge.
By the way, the loud transient that causes the blocking doesn't have to be in the audio range! It can be a Radio Frequency transient that made it through the amp...the needle of the turntable hitting a piece of dust, the CD player losing timing for an instant and misreading the digital code, a burst of RF interference from some idiot with an illegally over-powered CB transmitter...so amps that have specs where the treble goes to 500 KHz or some such crazy number may not be so good after all. The old Heathkit AA-151 only had flat response in the treble to 15 KHz, above which it fell off steadily, and you know what? It's a sweet, sweet sounding amp. I think the total bandwidth was only to about 150 KHz max, which is plenty for an audio amp. So, once again, numbers in audio amps can not only be misleading, they can mislead you to much worse sound for more money.
Note: Max's design at AngelFire (see links, near top) for the EL-34 PP power amp is a notable, and educational, exception to this topic of "blocking". It turns out, that if the output stage has tons of reserve capability, blocking ceases to be much - or any - of an issue - because the output stage is NOT being pushed to it's limits. Isn't that cool? So, what this means is that direct coupling to an output stage is not necessarily the only way to avoid "blocking" - you can capacitor-couple if you design the output stage so it's "breathing easy", even with high power transients. Cool, huh? What would probably be the best of both worlds? Direct coupling, of course, driving the output stage with cathode followers or mosfet followers or tubelab's powerdriver circuit (see links for tubelab) AND "over-tubing" the output stage so it doesn't get pushed to the limits. But....if the output stage is over-designed so it doesn't get whacked up to the ceiling or smacked down to the floor....is it worth the extra complexity of direct-coupling? Hard to say. Your choice. Capacitor coupling is certainly easier, cheaper, and safer. Safer is good. Look carefully at Max's design. Remember that many of the problems we have to deal with in DIY amp design are the result of CHEAP design decisions by manufacturers trying to make enough profit to stay alive...some of these problems are "straw men"....they only exist because of costs, they are easy to eliminate once we get into the mindset of being a DIY'er, not a manufacturer. "Blocking" is a great example. Over-design the output stage and suddenly...."blocking" is not such a big deal.
Of course, it is a truism - a generally true truism, for once - that the main problem with SS amps is the harsh clipping (and almost ALL amps clip, don't kid yourself about that...even if it's just extremely brief, high amplitude transients that we sense more than hear....tubes just play nicer when it comes to clipping.)
But, in the end, despite all my fancy arguing, generations of audiophiles and musicians have simply learned through experience that a decent tube amp always sounds a lot better than a solid state amp (assuming they can hear the difference, of course...see my article "Listen Up!"). Are there some exceptions in the solid state amp world? Yes. Can I afford any of them? No. So, give a good but short-on-money guitarist the choice of a tube amp or a transistor amp - assuming he or she has just enough for the tube amp or a relative is going to buy it for him or her - which will he or she choose? The tube amp. They're no dummy. Why? That's a subject for a whole new article, which I will eventually get to.
We know some bits and pieces, yes...at the risk of repeating myself, but with a little more detail...we know that almost all amps always clip (we'll make an amp that's an exception, but the fact is that most amps clip)...and that when tubes clip they sound much nicer than solid state, which clips harshly. We know that tubes - used properly, that is - tend to have a "waterfall" distortion pattern where the second harmonic dominates, and distortion falls off quickly and usually doesn't go appreciably above fifth harmonic - and that this imitates nature, so our ears like it. Solid state amps generate odd numbered harmonics that go far higher...three, five, ten, twenty, a hundred, a thousandth harmonic above the fundamental...and our ears do NOT like these odd harmonics. (Some say we can't hear these higher odd harmonics. I think we can "sense" them - and Lynn Olson says he believes they mix with lower frequencies to create ugly artifacts in the sound we certainly can hear). But there's more to it. A tube - used properly - gives a sound that is warm and pleasing...but has a "bite" to it at the same time...with sound-stage width, height and depth...clarity....unbelievable realism for voice and mid-range instruments...and a satisfying quality. That's the crux of it, right there: we can use a million adjectives, but a good tube amp satisfies. A solid state amp may have power, clarity, frequency response, ridiculously low noise, ridiculously low distortion, but, in the end, it doesn't satisfy - there's something missing!! (a tube... :)
So at least one tube in an amp is absolutely necessary....if the sound of tubes (actually, the combination of great linearity - low distortion without resorting to huge amounts of gNFB - and the "waterfall" distortion pattern characteristic of triodes, anyway, dominated by second harmonic (but way down near the noise floor), then less 3rd, less 4th, etc.) matters to you.
Usually, there need to be a bunch of them. But there are a lot of things that have to be done in an amp that are NOT best done by tubes - that are not directly involved in voltage amplifying the audio signal and adding a pleasing "character" to it - and there is no reason to use tubes to do these other tasks. Using tubes to produce output power, or filter and regulate B+, or supply filament current, or convert voltage to current, or equalize frequencies, adds unnecessary noise, is expensive in money and space, and wastes tons of energy.
We do need to start being thoughtful about wasting energy...so we use a few tubes in an amp to get beautiful sound, and we do everything else with solid state to conserve energy and get the job done efficiently and accurately.
So, in this site, I'll be showing how to use solid state to give tubes the support they need to work superbly.
In this site, we'll build a superb filament supply using solid state that will make your tubes last far longer and at the same time eliminate hum and noise.
We'll make a filtered, regulated B+ supply that's stone-quiet, supplies gobs of power, and does not color the sound of the tubes.
I'll be showing how to do tone shaping and equalization using solid state components for far more accurate results that can be achieved with a tube, more cheaply, with a lot less energy usage (heating up filaments in extra tubes in extra tone stages wastes a lot of energy).
I'll also be showing how to faithfully take the sound of an output tube and translate that into output power using mosfets, instead of transformers, eliminating the coloration and distortion of transformers. This, by the way, is the exception to the rule for bi-amping tube amps. If the conversion of voltage to current is done by using a mosfet output instead of a transformer, then you CAN have all the bass you want. But, except for certain speakers (Klipsch Horns certainly come to mind), even with a hybrid tube/mosfet amp, bi-amping and sending the bass to separate subwoofers is STILL the best way to go. Otherwise you just have to do the crossover in the speaker cabinet instead, and it's much better done inside the amp in the first place.
If you like the idea of playing with mosfets, this site may revolutionize the entire idea of tube amps for you. If not, please feel free to go to sites using output transformers - there are certainly a bunch of great ones, and I'll list them on the right-hand side.
We'll actually be doing each part of an audio system ourselves, except the turntable cartridge...that's beyond even DIY'ers unless you have a really good open-stage microscope! I don't, at least not yet, so cartridges will have to wait - although a DIY Decca type cartridge is a dream of mine. Maybe someday. But we will do our own air-float radial-track tonearm...you can make it yourself from my kit, and it will blow away every tonearm in the world (OK, a little over-exaggerated there...let's just say pretty darned good for small money).
But we will start with amps, a piece at a time.
Some of the projects that will be posted here:
An auto-grid-bias board, complete with PCB and kit, if you want them, that allows you to keep an output push-pull pair in perfect balance, no matter the kind of amp or tubes used. It can also be used to control the grid bias on all the tubes in all the stages of the amp. It comes with built-in protection circuits that prevent tube-runaway if, for example, the amp should lose it's negative supply - normally a disaster in grid-biased amps, but not with this board....no worries...or if the output is dead shorted - again, normally a disaster, but not with this board.
I call this the Broskie/Knouse Auto-Grid-Bias board, because the central idea of the circuit - using an op amp in integrator mode to control the bias to the grid - was John Broskie's original brilliant idea. This circuit is my own implementation of his original idea. When I get the PCB's done and can send him a couple of finished ones, I'll ask his permission to include his name officially and even see if he would like to sell the kit through his site (tubecad - one of the best, if not the best, tube blogs on the planet - if you don't know it, go there now and read it all (it'll only take a few months)).
Here's the main link:http://www.tubecad.com/
An all 6BQ6GTB amp - an all tube amp using one of the cheapest of all old tubes, an old TV tube (horizontal deflector), that will sound as good as a $10,000 amp (well, close enough, anyway
) - with a total of ten bucks in the tubes. The beauty of this amp is you only need ONE tube type...you don't have to worry about five different types of tubes, and which one is going to get rare. All tubes will eventually get rare, I mean the old ones made in the 30's, 40's and 50's, but I can assure you the 6BQ6GTB will be among the very, very last to go...probably well beyond your kid's lifetime, so don't worry about it. Now, amps using the 6BQ6GTB have already been done, and brilliantly - here's the very best example I know of:
http://geek.scorpiorising.ca/GeeK_ZonE/index.php?topic=3278.0
by a truly brilliant electrical engineer who goes by the username Miles. If you don't mind using different tubes, by all means build his design. My design, for the fun of it, will use ONLY 6BQ6GTB's in all the stages - and it will also have a special feature Miles' amp doesn't, which is a "tone shaper" that allows you to modulate the "tone" of the amp from pentode to UL to triode Single Ended - but the really nice thing is that it will use only one tube type, and that tube type is A: dirt cheap, B: performs great, and C: was made in train-car loads for TV's that were never built - so it should be around a long, long, long time. (And nobody besides me and Miles and a few other crazies want them, so that's your good luck). And, unlike Miles' design - which, again, is superb, if you like output iron - in mine the output voltage-to-current transformation will be handled by mosfets, not output iron. So not only will this amp have ridiculously cheap tubes, a big chunk of expense - the OPT - will be cut down to pennies on the dollar.
An 813 amp capable of a thousand watts per channel. Hint: no output transformer. But not tube to speaker direct, that's really a non-starter, even though people persist in trying to make OTL amps work. Oh, it can be done, but not well. No, a truly different output stage - mosfet - that transforms the high voltage of the 813 to incredibly high current for speakers without a transformer. This will be one where you do NOT turn the volume up very much - all that power is for headroom for transients, NOT for continuous output - unless you happen to have speakers than can handle it. So, if you use this amp and turn the volume up to stadium-filling levels, you'd better have the right speakers, or you're going to burn your house down when your speakers explode into towers of flame. I'm not kidding.
How to mod an old Heathkit AA-151 from top to bottom - truly outrageous modding - taking an old, sweet-sounding integrated tube amp that includes a phono preamp, fixing all it's flaws, modding it to take easily obtained tubes (since some of the tubes in it are now rare and expensive and getting rarer by the day), and making it the heart of an outrageously expensive sounding system with magnificent bass - but it's still just an old tube amp you can pick up fairly cheap on ebay.
How to do the same thing to the old Heathkit AA-100.
A DIY air-floating radial tone-arm...transform just about any old, used turntable into one of the best in the world, and do it all yourself for pennies.
How to make a bench power supply that allows you to do just about ANYTHING on the bench - a real help when prototyping and testing circuits. There is not a bench power supply on ebay that comes close, and the old tube ones are not worth the money - you have to rebuild them completely to have anything worthwhile, and you still don't have all the supply you need to make prototypes of hybrid tube/SS amps - and new commercial supplies are not only incredibly expensive, none of them are truly set up with the DIY'ers making tube/SS hybrids in mind - so you might just as well build this one.
How to use synchronized mosfet fullwave bridges to transform AC filament supplies in old amps into DC supplies, without losing voltage and at the same time control the turn-on surge to protect filaments. Now, this is some serious SS fun. This makes using diodes look like trying to use stone axes to build a house.
A nice, simple, powerful pedal steel amp. Not a guitar amp, not a bass amp, a real pedal steel amp. For those very few special musicians in the world who can actually play one...
Yes, a first-class guitar amp capable of amazing tones, for home play and small-venue gigging. (But this will be AFTER I build Guido's guitar amp and then figure out how to tweak the design to my own version (mosfet output; distortion in the tubes driving the mosfets)....if you want to build a guitar amp, don't wait for me (it's gonna be a while), build Guido's...or maybe you can offer him enough money to build one for you.
). The link to his website is in the list of favorite links on the right side of this page; just look for Guido's Site.Eventually, a personal, highly portable FM receiver you can carry in your pocket and pull in that weak classical station you can barely get and listen with great pleasure. It will have to have a digital option eventually, also, since digital radio is inevitable, but we'll start with analog, since analog will still be with us...thank goodness. (I'm actually counting on this super-nice FM geek in Denmark, Mikkel, to create the receiver board part...see his very cool website and great projects with PCB's, (he is a MASTER PCB designer), he's listed in the favorite links to the right
...there are two of them, Mikkel's Tube Site, and Mikkel's Projects Site)Please note this blog will also be separated into categories, such as: Great Sites for Tube Audio (with some reservations, of course), Rules for Joining Tube Forums and Avoid Becoming Unwelcome (or How to Get Help Without Getting Beaten Up), Twenty Rules for Tube Audio, Things That Really Are Baloney (and You Shouldn't Waste Your Money On), Filament Supplies, Power Supplies for B+, The Biggest Differences Between Guitar Amp and Real Hi Fi Amps), and so on. You may note I'm not a great fan of forums. I've belonged to a bunch of them, and they have gems of info - but you have to know how to wade through all the bullshit, and you post at peril...there are a lot of sharks that just love to cut down any idea they didn't come up with themselves. You're probably best off "lurking and learning". But more on that later.
When I figure out how to do it, I will be asking for comments, improvements, errors if you see something - not a free-for-all forum, but if you have something helpful to say I'll post it along with attribution to you, with thanks. This site will not have a forum, it will have a "soiree" - where ideas can be shared safely, where truly original thoughts are welcome - but where "shouters on soap-boxes" and "old crabs" can't get through the door. If you're new to tube forums, I'll give you a few suggestions:
funwithtubes at yahoo...the email forum is on yahoo, the home site for the email forum is at
http://www.angelfire.com/electronic/funwithtubes/
Max keeps the peace on the forum, and the forum really does have a nice feeling and tone to it, and his home site (above) has great info and some great project amps on it. You would do well to just start at his site and build his designs.
http://geek.scorpiorising.ca/GeeK_ZonE/ (although be cautious; read my Rules for Joining a Forum and Avoid Becoming Unwelcome before going here - for starters, just lurk, really try to avoid the impulse to jump in with a stupid question - in general, it's got super members and some real experts (Miles, Yves, Tom, Gregg, etc.). You're best off simply finding a project by a member you like and building it.
Very useful links for many of the old-time members of GeeK_ZonE above - all of these guys really, really know some stuff about tube amps:
http://geek.scorpiorising.ca/links.html
http://www.classicvalve.ca/
is the website of Gregg the Geek who founded GeeK_ZonE above, with great STUFF.
not a forum...but a great site with some very valuable insights and great projects/products/kits by a thoughtful, hard-working, really hard-playing guy (he tests his Hi-Fi amp designs by hooking his guitar to them and playing at top volume, full distortion for a long time
- if it doesn't burst into flames it passes - now, that's cooooool. ):http://www.tubelab.com/
and he has a really easy Single-Ended amp kit that's a great starter for any DIY'er (and his kits can work just as well for guitar, which is very neat.) He also understands how to use mosfets with tubes, and he has a PowerDriver circuit that is, I think, one of the actual best break-throughs in DIY-tube-land in the current century. The link for the PowerDriver circuit can be a little hard to figure out, so here it is:
http://www.tubelab.com/powerdrive.htm
The link for the PCB boards that tubelab.com sells is here:
http://www.tubelab.com/PCB_order.htm
also not a forum...or at least I don't think so...but a site full of info and projects, by one of the world experts:
http://www.pmillett.com/
And, last but not least,
http://www.tubecad.com/
where you'll find the smartest audio articles ever written, by Platinum Brain Award Winner John Broskie, and some of the best amp kits available (PCB kits; you still have to make the box, install the controls, etc....but that's half the fun!) Here's the link for his yahoo store, where you can buy the PCB's or the full kits - like TubeLab.com, these are kits where you just can't go wrong, they are superb:
http://glass-ware.stores.yahoo.net/
By the way, if I have accidentally left out a worthy forum or DIY site, please feel free to show me the error of my ways and I'll take a look at including it here (once I figure out how to make the "contact me" thingie work...
).So why am I bothering with this site? Between AngelFire.com and GeeK_ZonE amd ClassicValve.ca and tubelab.com and tubecad.com, what more could you need?
Because I bring a different, slightly eccentric view to things, and if you want a source in addition to those listed above for amp designs, here's a good place to find one (when I get them up!). And, if you have an old Heathkit -151 (and eventually AA-100's), here's the place to make it brand spanking new, a truly fabulous modern amp in a sixty year old chassis (when I have time to get all that up also!).
Best Regards,
Charlie
Transformation Audio
P.S.: a few more links to cool sites, some of them small, odd, but with great tips (I'll eventually organize this into a category of recommended sites):
http://www.geofex.com/tektips.htm
(for various tips on prototyping; written for stomp box builders (guitar effects) but very helpful to tube amp prototypers and other purposes as well, although I see he's given up on the link for how to use a laser printer to make your own pcb's...I guess you either have to set up your own UV system for photo-sensitive coated copper, or use one of the commercial pcb makers...boards are now so cheap and the free software so powerful, including silk-screening labels and solder mask and tinning of the copper, that it hardly seems worthwhile to make your own by hand anymore. If anyone disagrees with this, and has a proven method for making your own (complicated) PCB's for much cheaper (without buying super expensive software) please let me know!! I'll definitely post any such link!!)
http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm
A timeless page that I hope never disappears from the web, containing essential information for understanding how to use mosfets appropriately in a tube amp...and why. You might want to print this one out, since if it disappears I don't know any other sources for it. I'd gladly copy it here, if I had permission. Perhaps I'll try to contact the author and see if he would like to have it posted, with attribution to him, of course, in other places, so it stands less of a chance of ever dying from the web.
http://www.vt4c.com/shop/program/main.php?group_id=2
For the adventurous, here's a link to a place in Hong-Kong that sells simply amazing parts for making amps. I have been told that yes, you wire your money, and yes, your stuff eventually shows up, against all odds and expectations...although I haven't tested it for myself yet. On the other hand, I have purchased test equipment from other companies in Hong Kong, wiring the money in advance, and I have to say it showed up, every time. Just make sure you follow their directions carefully; when the wired money shows up, they don't know who it came from or what is ordered or where to ship until you send an email that allows them to hook the two things together. Or use paypal. I'm not such a paypal fan, but if it works for you, go for it. The nice thing about paypal and Hong Kong is paypal automatically forwards the information along with the payment, so you don't have some poor Hèung Góng Yà hn guys scratching their heads and wondering what you paid for and where to send it.
