Low cost SET as DIY

[Marvel]

Shannon Parks has a SET amp he is about to release the parts list for. He thinks it will cost about $400-500. DAt the present, he is calling it get*set*go or GSG for short. It is a 6B4G Single Ended Triode Amplifier with 6SL7 Driver and 6AX5 Rectifier, with James 6113HS Output Transformers. Here is a pic of an assembled/built one. Stereo! The 6B4G is pretty much a 6 volt 2A3 on an octal base.

The one in the pic was built by Tom McNally.

[Marvel]

Here's a shot of the top plate with everything mounted. He built his so that you can work on it outside the wood chassis.

[Marvel]

I agree, Mark. I know some don't like to go the pcb route, but Shannon makes it pretty foolproof. His instructions are always good. He also makes some Dynaco ST-70 boards and other stuff. He has a forum at:

http://www.diytube.com

Lots of tweaking goes on as well.
Like I don't have enough to spend money on already. [:|]

[kev313]

I've never heard 'em, but in pictures the James products look really well constructed...like little Hashimotos.

[Daddy Dee]

What is the power of the 6B4G? I know 2A3 is usually around 3 or 3.5 watts.

[mike stehr]

It's a six volt 2A3. The wattage I'm thinking is the same.

$400-500 for a DIY SET amplifier is rather cheap in my opinion. It isn't that easy sourcing parts with that sort of budget, especially if it's a first time amp project. I bought a project for a 300B SET amplifier from a audio friend Dan Marshall four or five years ago.He scrounged parts for over a year or so for the project. He didn't finish it beyond breadboard, so he sold the project to me for 400 bucks. I sunk at least another 150 bucks to finish it.

Of course I got a pair of TJ 2.5 volt 300B's along with the project, some nice Scholl 10 watt OPT's with a 3600 ohm primary, and oil caps, a 4 henrie choke, with 6AU4 half-wave damper tubes.

And this is a one of a kind circuit cobbled and copyrighted by Dan Marshall.

I've got the James 6123HS 20 watt universal output transformers, and they are a nice sounding OPT. I have swapped them out in my SET amplifier for the 10 watt Scholl's that came with the kit, to see how they would sound compared to the Scholl's.

They are a sweet and smooth sounding OPT. But with the SET amp I prefer the Scholl's. The James are just a wee bit too sweet for my liking in the SET amp. The Scholl's are more neutral sounding, yet kinda sweet too. I dunno...I swapped OPT's and listened to the James OPT's for 2 weeks. Then swapped back to the Scholls.....I do recall thinking, hmmmm....that's better...

I've used the James 6123HS with single-ended breadboard configurations, using 6V6 and 6L6. I've had some pretty good results I think, favoring the 6V6.

I take it you order the PCB boards from Shannon Parks, and source everything else.

I wanna use 6B4G's for a DHT push-pull amp, or 2A3. At least start breadboarding ala mono version....one of these days...

[Marvel]

Mike,

He has a Bill of Materials that he updates on a semi regular basis, reflecting ordering everything from Mouser. You get the boards from Shannon. He has links for templates for top plates, panels, etc. He and the forum there really help out.

The trannies are the only high ticket item. He actually has everything released.

Bruce

[Guest " "]

Marvel

Nice thread. Very informative and helpful.

[Clipped and Shorn]

Last year I built a low cost diy 45/2A3 SRPP (6SL7s front end) stereo SE amp using James OPT from Euphonia Audio (in all liklihood a similar circuit to the one being discussed here ---possibly, but with different output tubes and rectifier--guess we would need to see the schematic to be sure. I think they (the James) were about $150 a pair. They sound pretty good to my ears and I was enjoying these amps for most of a year with the diy Valencias (at moderated volumes). The only OPTs comparable in price are Transcendar (US made/sold on eBay) or Hammonds, but the James, from most accounts are supposed to sound better.

Recently I put together 300B monoblocks using a pair of unused Sowter transformers (eBay bargain/compared to new from UK) but giving me 8/16 ohm taps--16 needed for Altec 515C and/or the Valencias (man these Sowters are hefty!). After some fiddling with tubes to get better bass, and some break-in period, this project (the JElabs 300B dx schematic) also sounded quite good (I can roll 27,37,56, or 76 tubes as well as different 6J5. Currently I am using 56 and some Sylvania 6J5GT (metal base) to desirable effect with EH 300B (hopefully soon to be replaced with Sohphia). Both of these amps are now being used in my multi amp system with the 300b driving Altec 515C (very sweet, and very excellent) and the 2A3 driving the (511/802drivers+JBL2404H). The James with the 2A3 only has 4/8ohm taps. I need 16 ohm for the JBL crossover and horn, so this is still sounding a bit "thin" to my ears (16ohm connected to my 8ohm taps...is this so wrong???) , but the amp on its own sounded decent driving my diy Valencia speakers (also 16ohm connected to 8ohm taps).

Both of these SET amps sound better to my ears in the tri-amp where I have 300 watts of SS (Carver) in the bottom below 200Hz, than they did driving horn 3-way systems on their own. Sound was a tad too bright for me at higher volume. This is just my ears here with what speakers I have on hand. I like to turn the volume up, and I have better results with both the MarkIIIs(pp6550) and/or my proto pCats (ppKT66) with the Valencia or OBs. But let me say, the SE amps with the right speakers are a revelation, and they have transformed my tri-amp system, especially where vocals are concerned! The 300B SE+Sowter OPT with the Altec 515C is pretty pretty pretty....darn good --now the heart of my tri-amp system.

I have concluded that it might be a bit tricky finding the right SE circuit and design to be the single amp for a horn system like most Klipsch. Obviously there are some great SE amps out there and particular components (OPT, caps, tubes, etc.) that can do this, I am just not sure one can count on just any SE circuit or design to fulfill this role apriori and is why Bob Lee, for example, is a dedicated breadboarder, trying and experimenting all the time in order to optimize the results heard on his beautiful Klipschorns. Bob has told me that some old Webster OPT he found in a vintage 2A3 organ amp, for example, are far superior to the Transcendar OPT he compared it to. I am thinking SE amps may be somewhat more "specific" than PP amps when it comes to the predictibility of sound with the speakers you might have. Best to get recommendations from those who have already tried and tested and experimented and spent lots of moolah in the process of pairing SE amps with particular speaker systems.

I just went for what information was freely shared online as far as schematics, eg. the JE labs designs (check out his site!), and also for using magic old radio tubes. I think there are many more schematics, and many which are not so freely shared online. Also I just went for less esoteric and less costly OPTs, it is possible to go nuts in that department. Fortunately I have enough systems that I could consequently find where best to use the amps as built first time out, otherwise I might have to start swapping OPTs and parts and circuit operating points, and at this time, that is not exactly my hobby, yet.

Mostly I am proud of the fact that these things work after I built them....nothing too creative, just following the online schematics and a few pointers...

(I am now pretty good at punching holes in a metal chassis....)

-? ? ? (©fini)

[Painful Reality]

Recently I put together 300B monoblocks using a pair of unused Sowter transformers (eBay bargain/compared to new from UK)

According to my "taste" Sowter, Partridge and MagneQuest are my favorite output transformers. I never liked the japanese/asian stuff (Tango, James, Tamura, etc...).

[Clipped and Shorn]

Colonel Painful Reality,

Thanks for mentioning the thumbs up on the Sowter iron. There was not much online review compared to the Japanese stuff that I could find. Had I not stumbled onto the good deal on the Sowters (which happen to have the 16 ohm tap I was looking for), I was also aware that the Plitron toroidal design had some serious fans and high recommendations, at least with 300B (not sure about their product with 2A3/45 etc.). Just curious, what you think about the Plitron toroidals? Also, what OPT might do the best job with 45/2A3 for the high frequency range (eg. 2kHz and up)?

-? ? ? (©fini)

[Clipped and Shorn]

Mark,

With all these nice tubes in the SE amps I have been building, I was wondering if it might be advisable to include a time delay B+ switch like you use in your BB preamps. The 300B SE uses a 5U4 and the 2A3/45 SE uses an old 80 in the rectifier dept. When is it a good idea to use that time delay switch? And, is it simply a component added or are other mods to the power supply necessary as well?

-? ? ? (©fini)

[Clipped and Shorn]

As mentioned, the James OPT with 2A3 is sounding a bit "thin" in the high frequency range where it is being used in my tri-amp. The JBL 3105 network would rather be seeing 16ohm and the James, as many currently available OPT for SE, typically have only 4 and 8 ohm taps. I am wondering how critical this frequency range is in any OPT, maybe I could just as easily be using an economical Hammond OPT which does have the 16ohm tap. Is the bass and mid range more of an issue with an OPT and could I just as easily use a Hammond without noticing any lack in quality up there in the high frequency range ?

I didn't realize the graph would copy so small, the green trace is the crossover with 8ohm dummy load, and the yellow trace is with 16ohm. I think it shows why there is a "thinner sound" at the crossover with the 8ohm and why I am motivated to find an OPT (for the 2A3 SE) that would have a 16 ohm tap.

[Clipped and Shorn]

Is this bigger....?

OK, I get it, the forum software automatically sizes the image. Sorry about that.

The amazing thing is that one can even find all this esoteric data on the internet, I mean this is a vintage JBL network 3105 and yet you can find charts and graphs for it as well as serious discussions and problem solving etc. If only we could solve world problems and save the planet as easily!

Maybe if THAT too was an interesting HOBBY we might make it.

-? ? ? (©fini)

PS. btw, I do realize the James 6123HS OPT has the 16ohm option, but these particular transformers seem to be less obtainable currently, the James 6113HS obtained from Euphonia Audio does not provide the 16ohm tap but are more available and more economical from them. I am thinking that I may very well try out a couple of the even more economical Hammond 125ESE or similar for a 45/46SE amp dedicated to just the high frequency range in the the triamp, unless I hear of strong recommendations to the contrary.

[mike stehr]

I dunno, I got a pair of the 6123HS around 3 years ago for $150. (From a local friend.)

Do you any vintage iron lying about? Sometimes you can get away with using a smallish PP output transformer (say, PP EL-84), and use it with a 45 tube without problems of saturation.

The guy I bought James OPT's from used a PP EL-84 Layfayette output transformer using 45 in SE with rather good results.

[Clipped and Shorn]

I dunno, I got a pair of the 6123HS around 3 years ago for $150. (From a local friend.)

Do you any vintage iron lying about? Sometimes you can get away with using a smallish PP output transformer (say, PP EL-84), and use it with a 45 tube without problems of saturation.

The guy I bought James OPT's from used a PP EL-84 Layfayette output transformer using 45 in SE with rather good results.

Vintage power transformers yes. Not so much on OPT. And certainly not a pair of them. I should check with fini who pulled things out of organ amps. What about organ amp OPTs? Also, Hammond has some very inexpensive SE OPTs, what do you think of those? Were organ amps stereo? or just have one OPT?

c7s

PS. Actually after a little bit of internet research and I guess the Hammond OPT are NOT the way to go for me. Guess I will try to score James 6123HS unless I stumble onto some vintage approximations.

[mike stehr]

What is this? Attack of the questions? Yikes.....

Yes, possibly.

Never tried the Hammond 125 series OPT's.

I dunno, I think most were mono with one OPT. Some tone cabinets with amplifiers, used more than one OPT in bi-amp configurations. I have some Hammond's like these.

Just don't be afraid to try things. Within reason, of course...

[Clipped and Shorn]

Mike,

Huh? I don't understand, did I say something....???

I like your idea of exploring some vintage OPTs, I will check that out. Bob Lee also has used some recycled OPTs from amps that were not SE in his #45SE breadboards.

I found some online chat concerning dissappointments with Hammond SE output transformers in the high frequency range, so that might not be best since that is where I need them to shine.

I did find someone online who does sell the James 6123HS which seem to have a good rep. Meanwhile I can maybe scrounge around for something to experiment with that will be a better bargain.

thanks.

C&S

What is this? Attack of the questions? Yikes.....

Yes, possibly.

Never tried the Hammond 125 series OPT's.

I dunno, I think most were mono with one OPT. Some tone cabinets with amplifiers, used more than one OPT in bi-amp configurations. I have some Hammond's like these.

Just don't be afraid to try things. Within reason, of course...

[Clipped and Shorn]

I guess what I should be asking is: what things should I be looking for when considering recycling a vintage output transformer for use with SE45? What is this "saturation" deal? What else should I consider? For example, If it has already been pulled how can I determine if it has a 16ohm tap?

C&S

[Painful Reality]

Colonel Painful Reality,

Thanks for mentioning the thumbs up on the Sowter iron. There was not much online review compared to the Japanese stuff that I could find. Had I not stumbled onto the good deal on the Sowters (which happen to have the 16 ohm tap I was looking for), I was also aware that the Plitron toroidal design had some serious fans and high recommendations, at least with 300B (not sure about their product with 2A3/45 etc.). Just curious, what you think about the Plitron toroidals? Also, what OPT might do the best job with 45/2A3 for the high frequency range (eg. 2kHz and up)?

-? ? ? (©fini)

The Plitron are absolutely great for a 300B amp. I built a JELab 300B type of amp using Plitron (2.5K primary impedance). It was within my best "non parafeed" sounding amps.

The only drawback is their size. These are HUGE. As for the OPT I do prefer for a 2A3/45, it would be the EXO36/EXO45 from MagneQuest (mind you I'm highly biased in favor of these). But you would need to go the parafedd route. The TFA204 from MQ would also be excellent in the air gapped category.