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In Reply to: RE: Fisher 400 receiver conversion posted by used-hifi on July 24, 2017 at 10:58:03
You'd have to drop the B+, kind of a lot. You don't want to go with cathode bias because then you won't get that extra bit of oomph from class B (this also prevents you from just slapping in some big 50 watt resistor to shed 150 volts), and the power supply is a voltage doubler, so you can't exactly just switch to a choke input filter. Then again, if you could lower the voltage produced by the power supply, now all the small signal tubes are going to be off. It's a can of worms for sure!
If the space and filament current are available, EL34's might be an option that's a little more workable. Depending on your 400, you might have 6.4K OT's or 10K OT's.
Follow Ups:
I am even less impressed with el34 tubes then 7591 variety!
I want 6v6!
Sorry, you can't have 6V6s. However, adding some filament power will allow you to use 6L6s. The filament winding already present will easily feed 4X 6L6 heaters. Add a 1 A./6.3 VAC filament trafo and you can easily energize 2X 6BL8s, etc. A pentode voltage amplifier, instead of a 'X7 section, will give you the extra gain needed to drive 6L6s.
You can entertain the thought of triode wired "finals", for extra "finesse".
Eli D.
I was also thinking 6L6 but the extra fill tfr will be a tight fit on that chassis. I think if it were me, I'd sell it and start with an amp designed for 6V6, the Bell 3030 comes to mind.
Thanks keep the information rolling :)
from what I gather 6v6 tubes will handle 400v easy but not the screen and I can drop voltage with a pot same with the neg bias supply.?
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