Bias pot placement on ptp

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Bias pot placement on ptp

Post by kansas-terry » Mon Jun 13, 2011 1:01 pm

Can I place the bias pot on a reissue ptp board and wire it just like the reglular jtm45 diagram shows, it shows a different value resistor.
Thanks for the help!

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Re: Bias pot placement on ptp

Post by soundguruman » Wed Jul 27, 2011 12:03 pm

you said "it" shows a different value resistor, what is "it"?
The schematic can be different, because we may change one resistor, to get more or less overall bias voltage. Some tubes adjust to the low side, and some to the high side.
If the bias will not adjust high enough or low enough, change the resistor to compensate for the tubes you are using. Change it so that the correct bias setting is in the middle of the adjustment range.
The bias voltage you need depends on the plate voltage, the type of tube, the OP transformer, and whether or not you want to run your tubes on the hot side, which sounds best.
Less bias will make it hotter, and sound better, less distortion, tubes live a shorter life.
More bias will make it cooler, and the tubes last longer, but more distortion.
Clue: if the tube turns red, you don't have enough bias voltage.

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