new 6GW8 amp

[Rohbiwan]

Hello all,

Design to include: 12ax7, EZ81 or 5Y3, a pair of 6GW8.

I’m designing a tube amp from scratch and would like to try the 6GW8 in pp. I’m thinking a 12ax7 pre and using the triodes in the 6GW8 for gain makeup after tone control loss and the other for PI duties. HOWEVER, I ran into a 6GW8pp design that had the long tail and PI PRIOR to the triodes – i have not seen this arrangement before and was wondering if anyone had come across pp triodes in a triode/pentode tube.

[Andy]

Do you have a link to the design? A typical amp is the PREAMP – TONE – PI – POWER, as you know so it sounds like the arrangement you are describing is typical.

[Rohbiwan]

of course I saved it, now if I could only find it :whistle:

The arrangement was typical, as you say, but it looked like both the triodes of the 6GW8s were post PI and in series with their pentodes. I believe a 12**7 (might have been an AU or AT) PI was feeding it. I have never seen triodes in push pull before as I am still green with tubes. Perhaps this explaination makes more sense. As soon as I find the circuit Ill post it.

Thanks

Bill

[beelzebum]

If you use 1/2 of your 12ax7 as an input, 1/2 as a split load (cathodyne) inverter, then use the triode section of your 6qw8s as driver stages to add gain for the pentode section. This should give you the early breakup of the cathodyne, along with the added gain normaly found in a long tailed pair. If you want you can balance the driver stages to make them look like a long tailed pair, but instead of grounding one of the grids, you use both inputs as a differential amplifier feeding the pentode sections.

[Author]

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