The UL feedback to the screens should have some advantage in that the screens have nearly the same non-linear gm function as the pentode g1 has, so the non-linearities largely are cancelling.
The Schade schemes, especially the driver cathode CFB one just mentioned above, have the advantage that more gain can be put into the local loop, but is a linear resistive feedback jousting with the 3/2 power forward pentode output gm (ie, it has to work harder).
"How about the 12BH7A or ECC99 or with rewiring the 6FQ7/6SN7! "
Sure, those should be a drop in. But not a whole lot more gm than 12AU7.
I might try some TV video tube with a frame grid. Say a 9DX based video pentode (trioded) with the other triode in the bottle used for the 12AT7 front end. With the pentode hidden in there, one could also try out some conventional Schade feedback to its plate, like the 50 Watt Amp in the RCA Receiving Tube Manual (its got the driver cathode fdbk and the Schade plate to plate fdbk together). Experimenters paradise. But probably not a good idea for a first amp build, could be an experimenters H-LL, depending on ones abilities, equipment, and patience.
The Schade schemes, especially the driver cathode CFB one just mentioned above, have the advantage that more gain can be put into the local loop, but is a linear resistive feedback jousting with the 3/2 power forward pentode output gm (ie, it has to work harder).
"How about the 12BH7A or ECC99 or with rewiring the 6FQ7/6SN7! "
Sure, those should be a drop in. But not a whole lot more gm than 12AU7.
I might try some TV video tube with a frame grid. Say a 9DX based video pentode (trioded) with the other triode in the bottle used for the 12AT7 front end. With the pentode hidden in there, one could also try out some conventional Schade feedback to its plate, like the 50 Watt Amp in the RCA Receiving Tube Manual (its got the driver cathode fdbk and the Schade plate to plate fdbk together). Experimenters paradise. But probably not a good idea for a first amp build, could be an experimenters H-LL, depending on ones abilities, equipment, and patience.
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I was just looking at the ST-125 mono block amp kit. His output is 11.5 lbs 1 less then mine. I know my opt is 5000 ohms is there a way around this. His kit is designed for
The recommended tube complement is 4 X KT88, 6550, KT90, KT100 or KT120 output tubes, 2 X 12BH7 (recommended) or 12AU7 driver tubes,
and a Weber WZ68 Copper cap solid state rectifier.
A-125M output transformer
4.625" H X 3.875" W X 4.25" D
Weight 11.5 pounds
Primary impedance 2200 ohms
Secondary impedance 4, 8 and 16 ohms
The recommended tube complement is 4 X KT88, 6550, KT90, KT100 or KT120 output tubes, 2 X 12BH7 (recommended) or 12AU7 driver tubes,
and a Weber WZ68 Copper cap solid state rectifier.
A-125M output transformer
4.625" H X 3.875" W X 4.25" D
Weight 11.5 pounds
Primary impedance 2200 ohms
Secondary impedance 4, 8 and 16 ohms
that is impedance not Resistance I am on the phone with him now. He says that it does not matter it will work fine? He is also said I should run 2 x 6550s per side. one OPT and stereo for like 120-140w. He is going to help me figure this out as he has it all in his head already. This is simple stuff to him. I trust him and he said if I go with a 600v current to the plates from this PT, should all come together very easy. According to him. He said start with 2 tubes and then try 4, He says that running 4 will require a few changes to the voltage to the plates, He also said running 4 will lower the temps and they will run cleaner and smoother.
He also said the plate voltage is determined by the PT and that he sent two schematics. 1 for the 700v PT running 6550s and one for the 600v PT running 8417s Though he said getting the 8417s now will be tough. And $$$.
I guess we will see
WO
He also said the plate voltage is determined by the PT and that he sent two schematics. 1 for the 700v PT running 6550s and one for the 600v PT running 8417s Though he said getting the 8417s now will be tough. And $$$.
I guess we will see
WO
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A 600 V power xfmr should get you around 770V for B+ (cap input filter) under load, which will give you around 200 Watts with the 4 tubes (70 V loss in the tubes) and the 5K OT. ( Wpeak = 700 x 700/1250, Wavg = Wpeak/2 ) But as Tubelab was saying, the newer audio tubes may not handle this HV B+ well. And awfully dangerous to work with too. Varying the size of the 1st cap in the CLC filter will allow anything from about 590 V to 770 V for B+.
That voltage (actually twice that B+) appears across two adjacent pins on the standard octal audio tubes (a dumb 6L6 design from way back). That's why George was recommending going with some high voltage rated (990V B+) TV Sweep tubes. Probably some Sweeps with plate caps.
That voltage (actually twice that B+) appears across two adjacent pins on the standard octal audio tubes (a dumb 6L6 design from way back). That's why George was recommending going with some high voltage rated (990V B+) TV Sweep tubes. Probably some Sweeps with plate caps.
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Aiken Amplification
This site (click technical) has many of the questions answered. UL Keroes is also there.
I get alot of correspondance from ambitious types who would love to build high power stuff without really knowing much about it. When things don't quite go to plan, then panic calls start ...."the old adage don't bit off more than one can chew" is too right here. Start with a smaller practical project, ECL82/EL84 or other small tubes and there's loads around in this class. Over time I've built up some pretty monster amps, some beyond lifting weight...but the humble 9W ECL82 sounds just as good for HiFi and also use it for guitar.
Those of us who were brought up in the epoch of steam trains and tube amps never had it so good in aquiring materials. I still drive and fire steam trains, but the common thing with all this, they require a learning curve. Implementing them in practise is quite another experience.
I started both with the theory in 1958 by evening tech college then Uni.
In 1961 I assembled the original KT88-50 amp and destroyed the LS by doing so with a guitar....at that period, speaker coils then were barely rated for half that power rating. The clue was to use as many in series/ parallel.
richy
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