Electronics > Beginners
what does "remote cutoff" mean?
ELS122:
I am constantly seeing these "remote cutoff" pentode's in rf stages. what does "remote cutoff" mean and what does it do?
ELS122:
and can I use it in an audio amplifier (guitar amp) and what effects will it add if it's usable?
TimFox:
A remote-cutoff tube is one where a relatively large negative grid voltage is required to reduce the cathode current to near zero (cutoff). In practice, this is done with a grid winding where the spacing is not constant along its length. It is roughly equivalent to two tubes in parallel, where the tube with a tight spacing cuts off at a lower grid bias, but the other continues to conduct up to a higher negative bias voltage. This grid structure is commonly used in pentodes, triodes, and mixer tubes in RF applications for better control of gain with small input signals.
They are not used in ordinary audio circuits, since they are inherently more non-linear than the “sharp cutoff” variety. Typical examples: 6AU6 (sharp) / 6BA6 (remote), or the older 6SJ7 (sharp) / 6SK7 (remote). If you compare the plate characteristics graphed in the data sheets for these pairs, you will see the difference.
In a guitar amplifier, you might exploit the distortion of the remote-cutoff tube, which would have large even-order harmonics at high levels.
ELS122:
Ok that cleared things up a lot, I might try to experiment whit remote cutoff pen tides in guitar amplifiers now. I will post if any interesting stuff happens when I try do use that kind of pentode
ELS122:
Wait so it would add a dc bias to the signal basically if it needs a lower voltage to “turn off” or will it just like respond linearly to the audio signal?
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