Location of screen taps on Triode A431S output transformers?

[thorpej]

House is still a construction zone, meaning my garage is not usable yet, and it's driving me nuts. But if I can't build, at least I can put thought experiments to paper, so another amp is on the drawing board.

I'm planning a 6550-based ultra-linear amplifier, and I'm considering using the Triode A431S output transformers for it. Load line analysis for 4.3K / 450V tells me I could expect 65W per channel before clipping sets in, which seems just about right for these transformers, but the plate curves in the GE data sheet assume 40% screen taps. Hence my question

FWIW, the topology I plan to use is "the usual" Mullard 5-20 style, but since I'm going to need more voltage swing to drive the 6550s I am going to experiment with the the initial voltage amp stage: direct-coupling the 12AX7 gain stage to the other triode in the same bottle configured as a cathode follower, and using the cathode follower to bootstrap the gain stage. Costs an extra tube, but it's still easy to direct-couple everything in the front end together without having to make any other adjustments.

 

[thorpej]

Hm, "never mind"? I went back and looked at @kward's KT120 Mk2 amp, and his schematics show 33% for the A431S. The Hammond 1650NA is another candidate, but the A431S has better specs on paper other than the screen tap location.

(Haha, this would be the first case for me where the Hammond was the lower-cost alternative...)

 

[kward]

Yup, 33% voltage taps on the Triode A431S, which was the same as Dynaco used on the original A431 I believe. If you go with the 1650NA, I'd be very curious to see how its HF performance stacks up to the Triode Dynaco clones.