MagneQuest/Peerless Forum

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RE: TFA-204 300B Operating Points

Posted by jdrouin on March 7, 2017 at 16:13:49:
Thanks, triode3. I will keep these comments in mind, for sure. Right now I'm just interested in reproducing George's design accurately rather than modifying it, even though it uses a lot of unorthodox methods.

For instance, the power supply choke is indeed in the ground leg, according to the owner who derived the schematic (which might not be totally accurate):

http://www.diyaudio.com/forums/tubes-valves/227426-wright-audio-wpa-3-5-humpot-schematics-2.html#post3405178

Kyle K also said this in conversation with Paul Joppa on 02/12/2013:

"On the WPA 3.5 I looked at, the choke was in the ground leg"

which you can land at here:

http://www.meter.com/cgi/t.mpl?f=set&m=72462

There's another thread, I think at the Bottlehead forum, which describes the choke in the negative leg as "an old school trick" that George used.

I've looked at a tone of gut shots of the WPA 3.5 and the Mono 8, and the components seem to conform to the values expressed in that owner's schematic -- and even more interesting, is that they're the same for the WPA 3.5 and the Mono 8, even though the Mono 8 ran 300Bs with the FS-030 at presumably a higher voltage and current rating than the one-off I heard that used the TFA-204.

I'm learning LTSpice right now in order to model the schematic and come up with some values. It's coming along, but I've not had luck modeling the power supply on this or the Fi Primer 300B, which is a little more straightforward.