Again Bias in SSS#002

[larsvictor]

Hello Everybody,

before starting my next bulid I´m trying to understand the different stages in the Steel String Singer circuit (#002).

According to that what Mr. Manning had written in another thread, it is possible to adjust the bias of CF-Triode grids and power tube grids by simply changing the resistance in the „tail“ of the cathode biasing network (130k resistor in the schematic). Calculating with the voltages documented in the original drawing, a range of 200k (+27k to 227k) should change the negative grid voltage of the CF triodes approx. +/- 25V. Since the CF is cathode biased the cathode voltage will follow the grid. Will the circuit change in the drawing below work ? (for those who don´t like tweaking on pcbs)

Thank you for reading. All opinions are welcome.
Victor

[Synchu]

I just used 75k tail resistor and 50k pot and it works fine.
Niki

[martin manning]

Will the circuit change in the drawing below work ?

That's exactly the right way to do it. I would think that +/- 10% would be enough range for the adjustment, once you get it centered with the right fixed resistor. Then you could use a 25k pot and have a more precise adjustment.

[larsvictor]

Thank you very much. Of course you´re right. A "smaller" pot allows more precision.