Farfisa Model B power supply

[m1989jmp]

Hi all,

can someone clarify which power supply configuration is this and does it really put 745VDC on output transformer CT?

If that voltage really ends up on EL34 anodes, which of the current production ones can take it? Or is it just a matter of keeping the screen voltage under max specs (which it does, 395VDC per schematic).

I guess if that anode voltage is too extreme, the supply could be split to provide 420ish VDC for OT CT?



The whole schematic is linked below:

http://music-electronics-forum.com/a...88-or200-2.pdf

Thanks.

[SergioD]

Hi. I was looking for this SCH, But is likely the link isn't working. Can you share it?
Thanks
in advance

[g1]

Hi. I was looking for this SCH, But is likely the link isn't working. Can you share it?
Thanks
in advance

Look here: https://music-electronics-forum.com/...526#post483526

[Jon Snell]

With full mains; 275 + 300 x 1.414 = 813volts (no load or bias current) for the Anodes. EL34s from the 60s can run on 900volts Anode to cathode. No idea about newer makers but Svetlana can certainly handle the heat.
395volts on the screens is also pushing it a bit; use 1k5 G2 resistors for safety.
A bit close to the edge for me even with old school valves.
807s will run nicely in this amplifier. (An 807 is a high voltage 6L6GC).

[trobbins]

I'd be intrigued at how stable that EL34 quad output stage is for low frequency, given global negative feedback and three capacitor couplings in the forward path. Perhaps the first corner frequency is low enough to not be a significant contributor to phase shift.

[35L6]

I don't get that screen supply . Why is it connected to the OT ?

[Helmholtz]

I don't get that screen supply . Why is it connected to the OT ?

Schematic error. Would cause a short otherwise.