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From: gilmore@casbah.acns.nwu.edu (Kevin Gilmore)
Subject: high power single ended class A tube amp
Date: 16 Jun 94 16:58:48 GMT

I have been reading and seeing numerous all triode, single
ended pure class A power amps show up, but they all have the
same problem. Not enough power. So I set out to design an
amplifier that is pure triode, single ended, pure class A
and have 200 watts or more of power output. Impossible you
say, well not really, its taken me almost 3 months to get
it together, and the sound is fabulous.

WARNING: Ultra high voltages that will not only kill you
but will also set your dead corpse on fire if you are not
careful.

Input tube is a 12ax7. Middle gain stage is a 12au7. The 
final output tube is a EIMAC (varian) Y831. You will also
need 3 100 watt 10k power resistors, a 50 uF/3000V output
capacitor, A suitable output transformer rated for atleast
200 watts, and that can withstand 1500V. You will also need
the special socket for the Y831, and a chassis where you
can force air over the tube at the rate of 300CFM.

The power supply needs to supply the following voltages.
3000V at .25 amp, .5 amp peak   (for each channel)
450V at .05 amp
150V at .02 amp

Building this is not for the faint of heart. I had access
to virtually all the parts by scraping an NRC induction
heating device plus other parts from a high power AM modulator.

The reason I am using the voltages above is thats what
the power supply chassis I have generates, I did not
want to have to modify it. It weighs almost 200 lbs and
requires 220V.

Each amplifier chassis weighs in at about 120 lbs.
The completed amplifier with power supply takes up an entire
5 foot rack panel.

Current richardson price on the output tube is $1700 each. You
can probably find some at a hamfest for a lot less.

When i finish the electronic version of the schematic it
will be in HPGL format, anyone who wants it can mail me.

gilmore at casbah.acns.nwu.edu