Rangemaster bias dependency on pot value

[doctornorbert]

Hi, I'm new here, great forum!

I have a question about Rangemaster transistor biasing. I have been experimenting with using a 25k pot instead of the usual 10k to try to get more gain. I have noticed that changing this pot value results in a lower collector voltage on the transistor. For example, an OC44 with the recommended collector voltage of -7V to ground with a 10k pot goes to -4V when using a 25k pot.

So, do I need to aim for a different bias point (other than the -7V recommended in the Geofex article), or should I aim for the normal bias point by tweaking the base and emittor resistor values?

Thanks in advance!

Norbert

[JHS]

Use a 10-12k as emitter R, and the bias will be near -7V again.
Overall the RM will be a bit sharper sounding, due to the 25K pot, a bit more upfront. Some few original RM use the 25K/12k combination too.

JHS

[doctornorbert]

Thanks, I'll try that!