• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Those Magnificent Television Tubes

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
Hi, I recently scored a few dozen TV tubes with 150v screen grids… (6/12/17DQ6, 6/17GE5, 6BQ6, 6JN6, 6CD6, etc…) And I would like to use them as my everyday listening tubes and save the nicer KT88s and 6L6GCs for when I have guests haha.

Would it be possible to maintain the UL and Triode modes ?

Are there “minimum” screen voltages that need to be respected? If so imagine any sort of modulating voltage feeding into the screen needs some sort of scaling and positive offset to ensure operation within an acceptable window…

Sorry if this has been asked a bunch of times before, I am unable to find a “satisfying” answer. Yes I did see the “UNSET” thread but it really has me scratching my head…

Am I naively asking for the holy grail?
I use those tubes at 320V in triode mode (tie screen to plate through 240R/2W) with no issues for years. One of my Modular Amplifier 1 configurations uses them. The screen is always a slightly lower voltage than the plate so it doesn't draw much current. I wouldn't try it with UL though.
 

efm7

Member
2021-11-02 2:55 pm
I use those tubes at 320V in triode mode (tie screen to plate through 240R/2W) with no issues for years. One of my Modular Amplifier 1 configurations uses them. The screen is always a slightly lower voltage than the plate so it doesn't draw much current. I wouldn't try it with UL though.
Do you use cathode bias or fixed bias?

not sure that matters…

With the 6DQ6B at 300v, just tried 1k screen resistor in my fixed bias unit and it hasn’t gone into runaway yet so that’s encouraging… i’ll try stepping it down to 470R and 220R (i have screen resistors on a dial)