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Not much new being posted in DIY projects lately. Surely someone is working on something new and worth while to post about, including a photo or two.
I am getting tired of baiting Henry Pasternak et all for my amusement, someone post a NICE amp or build please. Yawn. :-)
Jeff Medwin
Follow Ups:
Thanks to DeathTubess pestering I have been measuring amps with ARTA and STEPs and tweaking feedback loops in a few amps.
major breakthrough here for me. quite exciting!
I recently had a failure of my 2a3 amp after reinstalling the 12ax7 and I've benched the thing while I figure out what to do next.
When I fished the big fulton power cord in to connect it to the primary 120 connection on the power transformer I managed to damage the jacket on the secondary wiring.. after some time I blew a fuse and ended up with a dead short. So the power transformer and the amp is sitting in a pile.
just prior to that I had reduced distortion from 5% at one watt to ~ 1.5%, just from changing from Hammond 1628SE to Magnequest DS-025. No other changes.
Again, measuring with ARTA, major breakthrough.
Last night I tried several different screen supplies, last of which was a low resistance choke after my B+ supply.. similar to the recomendations in your old JLH docs (jeff), and found a .02% decrease in distortion vs tying to the last cap in the B+.
I posted my first build a few weeks ago - probably not "a NICE amp or build" by your definition though. I am using JJ 2A3s in it right now, but have some EML 2A3Ms on the way. It might be time to post a follow-up soon.
Currently thinking about how to proceed with my digital source and am also tossing around some ideas for the next iteration of the 6C6-2A3 amp, but you probably would not be interested - it won't follow your formula.
FYI, putting a smiling emoticon(SP?) after a sentence does not disguise its intent.
Cheers.
“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck
Your posts were and are glorious !!! Always a pleasure to read. Thanks for contributing.
JM
Your posts can be controversial and your passion is admirable. In principle, the occasional spot of controversy is a positive thing. Your posts have certainly encouraged me to think about things differently, even if I have not ended up doing what you suggest, yet.
Man, just don't tell me your way is the only way or suggest things that might a newbie into trouble.
Keep well.
Cheers.
“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck
Since you asked, no amp work lately.
811B.
Been practicing measuring acoustics of speakers with ARTA.
Goofing around with x-overs, Zobel, notch filters, driver compensation, etc.
An interesting diversion from SE tube amps.
Hats off to you and Dennis if you guys got the Altec's dialed in right.
Dennis has owned at least two movie theatres in his life and set up scores more. The last one he owned had EIGHT A7-800s behind the screen, and he had it very right. I can guarantee you, he needed no NOTCH filters, Zoebels, etc, just a stock crossover with upgraded film caps and improved wiring.Maybe you should talk to him, ever have ??
Jeff Medwin
Edits: 07/20/14
I only have the 811B.The compression driver I got has an odd impedance vs. Hz plot.
It can benefit from a Zobel to flatten the impedance curve.
Since I only have a 12" woofer that is about 97dB measured with ARTA, the horn needed a compensation circuit to bring down the midrange to level match the highs better.
A lot of people get the Altec horn and use non-Altec drivers to build a system or experiment.
If I make some screw ups or wrong turns along the way, who cares?
I am having a lot of fun learning new things and that is what matters to me.
Edits: 07/20/14
I've been working to get this puppy in a proper chassis for a while...busted up my shoulder and all effort has stalled. The prototype achieved some pleasant results after much tweeking...
Went down the CF rabbit hole with some success...ultimately distortion levels resulting from pumping up the input voltage will be the killer.
Need to finish the build and start listening again...
Winter will be here soon enough...we'll start slinging solder again...
Stuben
Stuben
I went that route long time ago.
It was interesting but not my cup of tea.
Fast, articulate and very clear sounding.
Reminds me of a good PP amp.
I fell in love with the SE sound though.
Good Luck Though
DanL
Totally agree concerning DHT performance compared to tricking Pentodes into somewhat DHT performance...My listening amp will probably always be a DHT amp. Getting different sounds from Pentodes however has been fun..
Thanks...If I can't get what I want from the CF amp, a 2a3 scheme is already in the works. This is DIY...
Loads of fun
Stuben
Cool post. Tell me, have you PSUD2 simulated that supply with a step test of current? Three L/Cs in series to the Finals is inherently unstable and, if the values are not carefully chosen, it can ring like crazy, which we want to avoid. I was lazy and did not simulate it yet.
Jeff .
Jeff,
Thanks, I'm the lazy one...I have neglected to run the latest PS arrangement.... Will consider...
I have always considered transient pulls of current due to frequency induced load chances, and have been working under the premise that Chokes, when sized correctly for critical Inductance, provides "a Resistance to change in current" or simply put a "Surge"...
I also understand that an amplifier builders ultimate goal should be to provide amplification with no color. A wire with gain...
I will certainly get around to building a PS inspired by your posts.
Stuben
Steuben,
Awfully even-handed and a very nice response. Good attitude !!
If you want to use me to bounce ideas off of, please just contact me by private email. I have put in literally hundreds of hours on PSUD2 analysis, and may be able to assist you some.
Jeff
My post was a bit broken ..."the chokes resistance to current change" should be related to the chokes ability to filter AC through the production of CEMF and the "Surge" comment really describes the chokes ability hold energy while the rectifier is not conducting...I get in a hurry and forget everything I might have known...
I can run the calcs on my own...it's always nice to bounce stuff off the other inmates...although that was not my intent...just providing a short break from the blahs... ;> )
What are your thoughts on an amps ability to provide current upon frequency induced load changes...?? This subject has always fascinated me.
Stuben
Stock ( top ) versus a very quick suggestion ( bottom ).FILTER TO FINALS : Smoother settle below, quicker total recovery ( 200 mS versus 500 mS ) at the expense of higher Z, which can be ameliorated with lower DCR audio magnetics, 20 Ohms and less.
The G2 and front end supply will "see" the odd settling of the Finals, in the top simulation, and that is not good. I guessed at DCR values, used what is typical in both simulations.
Jeff Medwin
Edits: 07/20/14 07/20/14
Higher 'Z' ? I had no idea you could measure impedence on PSUD2 . At what frequency was this measurement taken ? ...and what was the actual impedence ?Al
Edits: 07/20/14
Hi Al,Follow this. In the top simulation, the voltage dropped on the current step, from about 286.88 VDC to a settled VDC of about 283.00, a 3.88 VDC drop.
In the bottom simulation, the voltage dropped on the current step from about 344.70 to about 334.01 VDC, a 10.69 VDC drop.
In each case, the current change was 14 mA. or .014 A.
Ohms Law, Voltage over current equals resistance.
3.88 VDC divided by .014 A. is 277 Ohms.
10.69 VDC divided by .014 A. is 763 Ohms.
277 Ohms versus 763 Ohms. This math, Ohm's Law, can be applied to any current step in PSUD2.
Are we two now on the same page ? Hope so.
One other point I'd like to make. Over the last couple of years, I have changed my priorities on Power Supplies and PSUD2. I no longer believe that the "lowest Z" is the best sounding supply. If that were the case, everything I built would have a solid state rectifier, yet I LIKE the sound of directly heated vacuum tube rectifiers over Crees, etc. and I will use vacuum rectifiers with no cathodes, despite their higher Z. I prefer the sound of ONE dual rectifier tube, and will not parallel tubes in my DC circuits any more. I also have greatly relaxed my desire for the fastest settling supply, like under 50 mS as per John Swenson. This under 50 mS comes at a price, of an overshooting, sometimes ragged step response. In 2014, I look to have a SMOOTH step response as one of several simultaneously combined priorites, so I have veered from the writings of Hasquin and Swenson, and am pleased to do things now as "I" like to do them, despite "theory ". Dealer's choice !! Live, listen and learn.
Regards,
Jeff Medwin
Edits: 07/20/14 07/20/14 07/20/14
That is not impedence . What you describe is a phenomenon unique to PSUD , it does not happen in a real amplifier . You are describing the settling time of the simulation .
I don't see Hasquin or Swenson here much any more . I think you've scared them off ;)
Al
Jeff, your troll is uninspired and I was planning on ignoring it. But then I started thinking about something I've been meaning to say for a while, and now seems as good a time as any to talk abut it.I know this will horrify some of you, but I have reached the point in my career as an enthusiast of reproduced music (notice, I did not say "audiophile") where I just don't care anymore about "hi-fi." Correction: I do care about "hi-fi" to the extent that when I listen to music I want it to sound clean and clear and realistic. But having owned and/or listened to many audio systems over the years, I honestly feel that most modern equipment is just really, really good, and the differences between them are increasingly irrelevant. The audiophile passion for obsessing over the tiniest details of so-called "sound quality" has ceased to interest me. Audio reviews (I still subscribe to "Stereophile," though I give it probably about ten minutes of attention every month) seem pointless and ridiculous to me. There is nothing of interest left for them to say.
In my opinion, well-designed equipment, solid-state or tube, vinyl or CD, sounds great. The biggest differences are in the speakers, turntables, cartridges, and the room setup. A system either sounds right or it doesn't, and the difference is immediately obvious to me. I find nothing wrong with a good solid-state amplifier, and worrying about "skewed sonics" and other such malarky seems to me to have absolutely nothing to do with music, and only detracts from whatever enjoyment I get from the music.
"Audiophilia nervosa" has no appeal for me.
Some of this, no doubt, has to do with my ongoing musical training. Jeff, you once described yourself here as a "musically sensitive listener." I have been taking serious piano lessons for twelve years now. I'm currently learning Beethoven piano sonata #30, op. 109. One of the most magnificent pieces of music ever composed, IMHO. This is a very challenging piece to play, and it's not just because of the technical difficulties. It's because of the profundity and subtlety of the musical ideas inherent in the piece. The differences between a superb and a mundane performance are easy to hear on even the most modest system. It does not take an esoteric SET/horn system to perceive them.
I defy you, as a "musically sensitive listener," to say one relevant, non-trivial thing about what makes for a musical performance of op. 109, or any other piece of important music, for that matter.
It's become apparent to me that the things audiophiles listen for, by and large, are orthogonal to the business of music. Being an audiophile in the contemporary sense is an interesting hobby (for some), but it is distinct from music appreciation. That's probably why, as the cliche goes, most musicians have crappy audio systems. They are listening for something different.
I have most recently built a handful of solid-state amplifiers, the last of which is really quite nice to my ears. It's currently on loan to my friend, Bryan, who uses it with a pair of Reference 3A MM de Capo speakers. It's a very, very nice system. Due to WAF issues, I don't have the right environment to set up real high-end loudspeakers optimally in my listening room. So I don't really do "serious listening," which saddens me, but it's one of the compromises I've been forced to accept in my life. But I can tell you confidently that for my purposes, that amp and those speakers and my Teres turntable, V15VxMR, and cheap op-amp phono preamp are all that I would ever need to be a very happy audiophile camper. One of these days, after the kids are done with college, I'll move to a new house with a dedicated listening room and set up my modest "dream" system, and that will be the end of it.
Another thing that has really turned me off to "hi-fi" is the proliferation of ever-more-exotic, overbuilt, overpriced boutique components that are obviously intended primarily to extract money from wealthy poseurs than to provide meaningful value or increments of performance. It's a hugely self-serving endeavor, IMHO, and the snake oil and general nonsense have become a huge turn-off to me.
I think hi-fi technology has matured to the point that the high-end as it was, say, back in the eighties, is largely irrelevant. Very nice systems can be had off the shelf for relatively affordable prices. Ninety-nine percent of what I read in hi-end magazines and on high-end forums strikes me as mental masturbation.
There will always be pleasure in the craft of building one's own audio equipment. This is a very legitimate and worthwhile hobby. And the really deep details of audio engineering remain complex and challenging for those who want to dig in that direction.
But the domain of "skewed sonics" and faith-based, golden ear self flagellation means nothing to me. Honestly, it never satisfied me. Call me names and deride me for not being a "real" audiophile. I just don't care. It's just nonsense words to me.
As far as I'm concerned, what you and your tweako ilk talk about is deeply divorced from good sound and from music. It's more of a cult and a mental illness that I am thrilled to have nothing to do with anymore.
-Henry
Edits: 07/19/14
Quote...
"Another thing that has really turned me off to "hi-fi" is the proliferation of ever-more-exotic, overbuilt, overpriced boutique components that are obviously intended primarily to extract money from wealthy poseurs than to provide meaningful value or increments of performance. It's a hugely self-serving endeavor, IMHO, and the snake oil and general nonsense have become a huge turn-off to me."
.....
LOL!
You mean like the latest proliferation of USB DACS built component per component on the data sheet reference design, all based around a single chip solution to boot!
Ahh, but that gold RCA SPDIF connector makes all the difference doesn't it?
I have had a similar attitude towards the HiFi, High End, Audiophile values system for over a decade, at least. Juxtaposed against this is a recent re-introduction to this way of thinking by virtue of my first amplifier build... and I don't like this type of thinking getting in the way of musical enjoyment!
I suppose it is because the new amp and interconnects expose an uncomfortable level aggressiveness in my source. Which leads to my main point: for me, it is more about what a system does not do, rather than what it does. I can genuinely enjoy music through 'most any system, except those that are overtly edgy - what some generalise as "solid state" or "digital". So, get a system that does not irritate. Enjoy.
From another perspective, ultimately the ability to simply/ purely experience music resides with an individual. None of us are completely musically enlightened, so we will (hopefully) prefer system types that make it easier for us to enjoy music - to get us closer to simply experiencing. However, the audiophillia I sometimes see is a different path - it leads towards a different ideal, where the pleasure (and pain) is in listening to - not through - a system and the analyses that follow.
Yes, this post has some apparent contradictions. Don't we all?
Cheers.
“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck
The question I grapple with constantly is whether the thought and effort and resources I invest in my hobbies are taking me in the direction of greater knowledge and enjoyment, or just sending me into a spiral of ever-increasing investment for ever-diminishg returns.
Back in the day, I had fewer bills to pay and a lot more money to blow seeking self-gratification in the form of toys. I was a perfectionist and never satisfied with what I had. I've come to recognize that perfectionism and the inevitable dissatisfaction that follows are a trap, a quirk of neurochemistry more than anything else. This is a trap many audiophiles fall into, I think, and one that the audiophile vendors are more than happy to encourage and feed.
"Perfectionist audio" is an interesting goal to pursue, but I think it's a goal you need to keep sort of off the side of your field of vision. If you fixate directly on it, it will drive you crazy. And in the process, you might lost track of some very important things, like perspective and reality.
I would hate myself if, in pursuit of proficiency in my hobby, I fooled myself into believing I was an "expert" on something when, in fact, I was completely full of shit. Not that I have anyone in particular in mind when I say this, LOL.
What I like about piano performance is that it's so damned difficult that there is absolutely zero danger (for me) of ever getting to the point that I'm driving myself nuts over irrelevant, trifling details. The opportunities for learning and growth in this activity are wide-open. It keeps me humble and the return on investment is high because I'll always be on the steep part of the learning curve.
I also happen to feel, for what it's worth, that studying music directly, rather than just thinking about sound, gets me a lot closer to something that is fundamentally profound and significant about, you know, what it means to be part of human culture. This is important to me, living at a time when the culture I live in seems to be going in the toilet.
As far as audio design goes, I've probably forgotten more than I know at this point about electronics. If I wanted to dedicate myself to audio engineering, I could easily find many paths to explore where the learning curve is as steep and rewarding as it is for piano playing. But in terms of just being able to listen to good music on a system I built myself, I mastered that a long time ago.
Someone on this forum once wrote, "What is there besides audio?" Hopefully that person is reading this and knows I'm talking about him. My answer would be, "Just about everything." There are so many interesting challenges out there and opportunities for growth and diversification.
I say, if you find yourself stagnating, doing the same thing and telling the same stories year after year, it's time to move on.
FWIW.
-Henry
I do care very much about sound quality but I've been using the same all-DHT 4P1L PSE amp for 2 years now. All filament bias, Lundahl interstage and OPT, no coupling capacitors or cathode bypasses. Ridiculously simple circuit but complex power supplies. And since I have about 150 4P1Ls which is all I need, I'm pretty much done with collecting stuff and building projects. Might still build a nice DAC one day, that's all.
But I'm also an active musician, and it's the music which lasts beyond the equipment. I love op 109. I like Arrau for the depth of sonority in the slow movement. But I'm more interested in songwriting. May do an online Berklee course. Active music making is great.
'Another thing that has really turned me off to "hi-fi" is the proliferation of ever-more-exotic, overbuilt, overpriced boutique components that are obviously intended primarily to extract money from wealthy poseurs than to provide meaningful value or increments of performance. It's a hugely self-serving endeavor, IMHO, and the snake oil and general nonsense have become a huge turn-off to me'
Dueland Cast capacitors spring to mind
Al
nt.
.
Freak out...Far out...In out....
OK...I'll play. This is what I'm working on today. Taking advantage of the nice weather to get the paintwork done on the chassis. Amps are 2x mono PP6A5G with UTC LS output and interstage transformers. Circuit is a truncated version of a Western Electric 1086C. Cosmetics are loosely homage to same.
I'll be using it with the pair of RCA LC-1A speakers I restored last year, and maybe a pair of 755A's.
These things take time, of course, but I'll post more photos when it's all together and running.
Dang Son, you better get that thing to a place you like and LEAVE it there. That's a double hernia waiting to happen!Great looking amp though. I love all the old iron and oil caps. I'll bet it sounds great.
Edits: 07/19/14
...for my well-being. :-)
What you see in the picture is not one amp--that would be almost immobile--it's actually two mono amps. Still heavy, but at least moveable.
BTW, they don't sound like anything yet. The photo is of a work in progress. They're not wired up yet. I have built this circuit before, though, with outstanding results.
I guess the tubes not being in the back amp fooled me. I can see it now that you have pointed it out. Much better situation, but you still better eat your wheaties on moving day!
With that much vintage iron and oil caps, it just has to sound good when finished.
Can I talk you into powder coating the chassis, rather than painting it ??
Jeff Medwin
Hi Jeff,
I've gone the powder coat route on other projects, and may for others in the future, but for this one I'm trying for a certain 'look' that's not available with that process.
That sounds very interesting. Do you have a schematic you can share, either the 1086C or your version?
Schematic for the Western Electric 86C should be available online. If you can't find it, let me know and I'll e-mail you a copy. It's basically an input transformer, followed by three identical single-ended voltage gain stages with 262A triodes, then an interstage transformer as phase-splitter/driver, then a pair of 300B in push-pull, then the output transformer. (There's also a super trick distortion cancelling circuit in the output stage, but I'm probably not going to mess with that on mine.)
Designed for amplifying the signal from a sound head, the 86C has way too much gain for home use, so in my amps I have eliminated the input trans and at least one of the voltage gain stages. I'm also not using WECo tubes, since I don't have any 262A's, and my 300B's are slated for other uses.
So my amps will only have one or two of the input gain stages (depending on how much gain I end up needing). I'll be using 56 or 27 type tubes in place of the 262A's. Pretty similar, really. Interstage transformers are UTC LS19's, output tubes are 6A5G's (like a 2A3, but with center-tapped 6.3V heaters). Output transformers are UTC LS57's.
I'm trying to stick with all NOS or vintage parts. Power iron is Chicago transformer Co., chokes are UTC CG series, caps are paper-in-oil. Even the power and signal connectors are NOS old-timey stuff. I'm planning on making a wiring loom and tying the bundles. We'll see how that goes. Chassis are 1/8 inch aluminum, welded at the corners.
Sorry, I don't have a schematic to post. I have 'textbook' values that I'll be starting with, but really, I won't have final values for everything until I start putting it together and check voltages and operating points.
Thanks for the explanation. I found a schematic for the 86B.
I am curious why you chose the 86 as a starting point (not critical, just curious). I have heard a pair of 124 amps a few times and was very impressed so I have a lot of respect for the old WE designs. As you probably know, the 124 uses a paraphase inverter and has 350B outputs.
Totally valid question, what with all the options available. The 86 was sort of the 'big brother' to the classic Western Electric model 91-A/B amps in the 1930's, and it just seemed interesting.
I have built the circuit before, years ago, first using UTC HA-106 IT's and Peerless S-226-Q OT's, and it was one of the better sounding amps I've heard or made. I later made another one with LS-21's and HA-135's. With good iron, you can't really go wrong with the basic concept.
Hi gilmorneau-
Stumbled across your amp pics searching for UTC schematics. I have a pair of LS-21 and LS-57 for an amp project. Your project looks great! I hope you got them finished!
As the LS-21 is only 0ma on the primary, how did you use it? Do you have any reference scheme?
Than you- Kent
Just found this post--hope you're still watching, Kent.
Anyway, the way to use the LS21 is parafeed, which is what '0 ma DC' implies it was designed for. That is, you don't run the plate current of the driver tube through the primary of the transformer, you run it through a resistor (like any normal plate-load resistor) and block the DC from the primary with a coupling capacitor. That way, no DC gets into the transformer primary. There are many advantages to doing it this way. It's explained in some detail in the Radiotron Designer's Handbook. If you don't have one, most libraries do, and it's a good read.
For examples of the circuit, see the schematic for the Western Electric 86C (should be able to find it online). Or check the link below for Jeff's simpler but similar approach. The schematic in the link has a lot of notes on it, and Jeff favors multiple capacitors where one will do, but it's really a very simple circuit, and should illustrate how parafeed is done.
I've been up to my ass in alligators for a couple of years now (i.e. really, really busy), so, no, I haven't finished the PP6A5G amps yet. I think I'll dig them out and try and work on them some, though. Seems like a good way to blow a long weekend. :-)
Thanks, gilmorneau! Duh, should have seen that blocking cap. Parafeed, indeed. Thank you for the link. I think I have a pair of LS-40's, HA-106's and HA-107's as well. Will need to dig them out and see if I can cobble together some all UTC transformer-coupled amplifiers!
If you can find it, there's a really good all UTC transformer coupled amplifier schematic in an old issue of Audio Engineering magazine. I looked for my copy, but can't seem to locate it. The article was called 'for golden ears only' or something like that. I'm guessing around 1955-ish. It uses a single triode input stage, then a UTC A-18 to split phase, a push-pull triode driver with UTC HA-107 (or LS22), and push-pull 2A3/6A3/6B4G/6A5G outputs with UTC LS-55 (or LS-57). There's a small amount of local feedback on the driver stage to improve linearity, and a few other interesting tricks to satisfy the scope. I always wanted to build that amp, but never got around to it. Now I don't have any of the transformers anymore.
If you can't find it, and you're seriously interested, I could probably find it at our University library--I think that's where I got it before. E-mail me offline if you want to pursue it.
I looked through my Audio Anthologies. The only one that seems sort-of similar to your description is the 30 watt Hi Fidelity Audio Amplifier from 1947. IIRC, one of the very few (if not the only one) amplifiers in Audio Engineering that used the 300A or B as the output tube.
It has a chart in the article for different brands of input, interstage and output transformers suitable for the design. Fo UTC, they recommend the LS12, LS22 and the LS6L4. Circuit is Low impedance in, no single driver tube. No feedback. It also has a tone control circuit.
Could that be the one you're thinking about? If not, I'd really appreciate the schematic you mentioned!
Regards- Kent
I am familiar with the 300b amp in the Audio Anthology, but that's not the one I'm referring to. For the 'Golden Ears' amp you have to go to the source, i.e. the original Audio Engineering magazine. That article was never reprinted in the Audio Anthology series.
I'll see if I can dig it up for you.
I think I found it- Jan/Feb 1954. Can only find January on line. Was this the one?-
https://archive.org/details/am-1954-01
Starts on page 18. Uses 12AU7, 12AX7, 9002, 6C4, 6AR6 (in triode). Differential input, no input transformer. Pic shows UTC OPT iron. Poss more info in the Feb 1954 issue. Interesting differential fb around the drivers and outputs and a single-ended loop to the 2nd stage.
-Kent
Sorry, that's not the one I meant either.
I did some looking online and finally found it. I was way off on the date I gave you--the article actually appeared in the April 1950 issue, starting on page 13. The schematic appears on page 15. The link below should get you there.
Note that the schematic contains a few typographical errors, most obviously in identifying the phase splitter transformer as an A-16, when it pretty much has to be an A-18 (the A-16 doesn't have a split secondary). Also, the choke used to force balance in the driver is identified as a '5-25', when it should be 'S-25', which is a UTC Special Series choke spec'd at 30H, 30mA AFAIK. There may be more errors, it would be worth checking.
In a letter to the editor in a later issue, a writer takes exception to the claim of originality of the circuit, saying the same circuit, using the same UTC transformers, had been published in the January 1946 issue of Electronics magazine. I couldn't find that one.
If you have all the old UTC transformers, I'd love to see this amplifier built. Keep me posted, for sure. For stereo, you'll need a pair each of A-18, HA-107 (or LS-22), and LS-55 (or LS-57). The power transformers and chokes could be UTC as spec'd in the article, but modern substitutes would work fine. Not sure why the author chose 6C4's for input and driver, I'd probably use octals--6J5 and 6SN7, but that's just me.
I have two amps and a preamp or two in the queue to build as well as some loudspeakers and subs to case up, but I'd rather be out in the sun on nice days biking, hanging out with friends or doing yard/house work. Here in Wisconsin such nice days are limited. Long cold nights and snow make for good seasons of time at the electronics bench.
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