What output tubes do plan on using. You mention a 6JH5 which is a non compatible triode, also the 6HJ5 which will make 125 WPC with some mods, but it eats 2.25 amps of heater current per tube. This would require a larger power transformer.
All of the three tubes that Pete originally specified have 1.2 amp heaters, but have a 550 mA maximum peak plate current so there is a limitation on how low you can go on the OPT impedance. I know those little tubes can make big power (80+ watts) but they need more than 400 volts to get there. I hit a wall at 3300 ohms with the little tubes, but I was running over 450 volts. I would say that 5K or even 4K is a safe bet on 340 volts or so, but 3.3K may not be. I have not actually tried any of these combinations. I eventually built three of these boards and all ran 6HJ5's or 6HD5's into 3300 ohms on about 600 volts for 125 WPC. Two of the three are still alive, but the third was my test mule which never got built into a complete amp and is still in a box here somewhere.
Ugh, details matter! Mixed up the squence of the letters.
Output tubes: 6HJ5
Since the 6HJ5 require so much heater current I was going to use this Edcor transformer with the heater windings paralleled for a total capacity of 12A
https://edcorusa.com/collections/tu...30v-100ma-dual-6-3v-6a?variant=41561680249019
The 700V HV winding will also get a B+ that is pushing 500V.
I am thinking somewhere betweem 4K-6.6K with the above PT and 6HJ5 tubes.
That will work. I ran 6HJ5's at 600 volts into 3300 ohms to get 125 WPC. The amp I gave to my boss nearly 10 years ago is still running its original tubes. I don't know how much he used it, but I do know it worked hard pushing some inefficient Magnepans that were formerly fed by a monster solid state amp.
I still have this particular project here in an unfinished state but did find some opt's 6600 ohms/40W for it recently so might be tempted to work on it again. Board has actually been soldered for years. Good to hear others are still building it and good to see George chime in.
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I spent several years tinkering with these boards when I lived in Florida. When my 41 year career at Motorola came to an end in 2014, we packed up everything and moved north to retire. Yes, much of my life has been counter to common tradition. Everything we moved was stuffed into various storage locations and eight years later, we are still "box shopping" in mystery boxes that were hastily packed when we had 3 weeks to get out of a house that we lived in for 37 years.
I recently opened a box full of red boards. It wasn't what I was looking for, so I put it back on the shelf. I just went back to find that I still have my original test mule from all those experiments, and another partially populated board that has never seen power. The board with the heat sink in the middle is the test mule. I was also experimenting with Pete's driver boards (also red) and there were some of them in the box, but I know that one fell victim to a power cable that was plugged in backwards making for some crispy and messy parts.
I doubt that I'll ever get back to these since I have found new ways to make big power. Those experiments start at post #445 here:
https://www.diyaudio.com/community/threads/unset-beta-board-build.376124/page-23
Somewhere back in this long thread there is a big red board 4 X 35LR6 tubes and a reading of over 500 watts on the HP8903A. Here there are three small green boards and 512 watts at 3.79% THD. I saw 525 watts @5% but the 15 amp bench breaker blew before I could get a picture or turn it up further.
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George, I have been following your unset adventures with interest although it's probaby not for me, The big red board has been in a box for a long time here as well, for other reasons although I could say in general life and ADD which makes starting projects fun but finishing them hard - you understand. I need to finish my ZM SissySIT amp first, but the Pass ACA I bought finished from another DIYer is actually so good that there is no real hurry. Thankfully there is a lot of inspiration here and such great people like you. If and when I finish something I will try and post it.
I fully understand the ADD / ADHD thing. I also have lots of unfinished projects. The 1 KW (500 WPC) tube amp is something that I have talked about for well over a dozen years, and I have most of the parts for. I realize that I need to build it before I get too old to lift it.
Then there are these two shiny green objects on my bench calling my name. These are solid state amp boards based on the UNSET design. Can we say FETSET? There is a box full of BIG mosfets and J-fets on my bench near those boards, and a pair of 600 ohm SET OPT's from Toroidy. It would be cool to build a tubeless SET that made 30 WPC. I can hear the cries....Why don't you change your name to Transistorlab?
https://www.diyaudio.com/community/threads/schade-common-gate-scg-preamp.380487/
Then there are these two shiny green objects on my bench calling my name. These are solid state amp boards based on the UNSET design. Can we say FETSET? There is a box full of BIG mosfets and J-fets on my bench near those boards, and a pair of 600 ohm SET OPT's from Toroidy. It would be cool to build a tubeless SET that made 30 WPC. I can hear the cries....Why don't you change your name to Transistorlab?
https://www.diyaudio.com/community/threads/schade-common-gate-scg-preamp.380487/
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Could have been a voltage issue, resistors have not only power (actual temperatur/life expectance), but also voltage limitations that have to be obeyed, some are limited to 250V, some 350V, seldom 500V or more. Also, when a resistor is rated for military use the otherwise same resistor is derated. 0,5W can become 0,25W or even less. Use two 0,5W 500k in serial and you are good even with the 250V types
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I plan on building the DCPP with 6HJ5 output tubes and a higer B+.
I was going to use this Edcore PT
https://edcorusa.com/products/xpwr0...00ma-dual-6-3v-6a?_pos=1&_sid=be60ca791&_ss=r
Which should give me a little under 500V for the B+
For those who have increased the B+ have you adjusted the preamp dropping resistors (1K) R48 & R49 to keep the preamp voltages inline with Pete's original design?
I was going to use this Edcore PT
https://edcorusa.com/products/xpwr0...00ma-dual-6-3v-6a?_pos=1&_sid=be60ca791&_ss=r
Which should give me a little under 500V for the B+
For those who have increased the B+ have you adjusted the preamp dropping resistors (1K) R48 & R49 to keep the preamp voltages inline with Pete's original design?
I bought all my parts from Digikey. They didn't have any either, so I used the 800v version. https://www.digikey.ca/en/products/...gTCBcDaIGIEUAKcAcA5VAGAwgTQBEAVAVQFp0CQBdAXyA
I would just buy the the stock parts from Mouser if they have them.
No idea what to replace IXCP10M45's with. It looks like George has been working on a replacement for his boards. Have a read thru it: https://www.diyaudio.com/community/threads/10m45s.390771/page-3
jeff
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I would trust a IXTP1R6N100D2 from Mouser or Digikey before I tried some possibly fake IXCP10M45S parts from China. Fake 10M45's have been found on Ebay for several years. They appear any time the real parts go into hiding.
BTW, what kind of Single Ended amp has 12 mosfets, 4 vacuum tubes and makes 30 to 35 WPC with 0.61% THD @ 25 watts?
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26HU5's. They are fed by the Meanwell SMPS on the left side of the picture. It's a 24 volt unit turned up to 26 volts. The output stage uses the same UNSET design as the push pull version that made 525 watts in post #1766 here. The driver is the board seen in post # 1768. I am now working on an all solid state output test board. The details of this madness is scattered throughout the SCG thread in the Pass Labs forum, starting with post #761:
https://www.diyaudio.com/community/threads/schade-common-gate-scg-preamp.380487/page-39
I'll open a new thread in the Tubelab forum with both of these designs as they shape up rather than continue to scatter my thoughts all over the place.
Didn't realize they had a voltage adjustment range. I guess it kinda makes sense. That's pretty handy.
jeff