The difference in topology between #002 filter section and the Dumbleland schematic is that 002 has a DC coupled C.F mixer just after the Filter recovery,where the schematic does not. If you wanted it exactly like 002 then you can always use the unused 1/2 triode on V2b as a DC coupled C.F. feeding the pre amp out and Mstr Vol..Then you would basically have the same preamp section as 002. Classic stack ,feeding filters, feeding DC.C.C.F..off to the P.II have been reading this topic and was wondering if the preamp design as posted is correct. Like Erwin I can say that the video of the Dumbleland 009 sounds and works identical to the sss002 i build. I did use a much bigger 100W OT with extended low frequency range.
I've run higher voltages too, however, one question? do you own an amp company?There are a lot of designs with a higher voltage on the screens than the maximum 400V in the data sheet that are working just fine. I use a pair in my own amp I build years ago on 470V (Va) and 468V (Vg2) wired like a regular pethode poweramp. It's been working for 14 years on the same tubes, nothing gets fried.
If so I would not recommend selling an amplifier to the general public that exceeds Max voltage ratings (that much) and try to stick to the advertised mfg data! if not you could open yourself up to some ugly lawsuits? Especially if someone gets injured or something catches fire. In the world of amp manufacturing we tend to lean more on the conservative side especially in regards to high Voltages I am pretty sure Dumble was aware of this .
Tony