Tubes Asylum

RE: I have biased tubes in the past above true ground but. .

76.90.100.230

Tre'

P

In Reply to: RE: I have biased tubes in the past above true ground but. . posted by John PA on October 22, 2024 at 09:38:58

Do not otherwise ground the DC filament supply. It will be grounded by this resistor network.

The combined resistor values of R2, P1 and R3 (in series) is in parallel with the filament so that will be an extra load on the filament supply.

Make R5 whatever value it needs to be, vs. the cathode current, to give 20 volts of cathode bias for the tube.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

Follow Ups:

RE: I have biased tubes in the past above true ground but. . - PakProtector 08:39:46 10/29/24 (2)
I think he is wanting to use filament bias. So to say, applying .01A at 20V and use a smaller cathode resistor. 20V/.01A=2000Ohm biasing resistance. Instead of something huge to give that same voltage but with only cathode current through it( and thus likely requiring a bypass cap ).

And a 2kOhm cathode R would likely find it useful to bypass in any case... :)

Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
- I wondered about that. That's a different conversation. - Tre' 12:08:01 10/30/24 (1)
  What tube operates on 1.25volts filament at only 10ma.? That seems insanely low.
  
  Tre'
  Have Fun and Enjoy the Music
  "Still Working the Problem"
  - beats me - PakProtector 02:30:34 11/02/24 (0)
    seems low, so I imagine that plate current would have to be small too...
    
    Douglas
    
    Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

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