Opto-trem driver tube bias?

[phydauex]

Hey All,
This falls under the "why" catagory. I'm building up (rebuilding actually) a Fender Bandmaster BF and getting to the trem section, and just thinking as I go, but why use a 100k cathode resistor on the 1/2 12Ax7 that drives the "bug". I've seen some of these circuits that set the bias with a 56k resistor. That seems so high that your basically shuting the tube off. Is there a reason to have it so high, like not driving the LDR too hard or something. Also conversly, if you wanted to have more intensity on tap could you use like a 27k or 47k resistor there? I'm just wondering how it all works.

thanks for any insights into the functioning of this circuit.
matt

[Enzo]

The tube is an oscillator, not a signal stage, it doesn;t have to pass signal, it has to turn off and on.

I am looking at AB763, not sure which you have. There is about 5v bias on that cathode, but what is the oscillation signal level? This stage has to turn the bulb on and then let it go off.

They increased it from 56k in the earlier version. Probably best to leave it that way.

[phydauex]

Yeah, just the basic AB763, just wondering really. I'll have to dig into oscillator how-to's. I just wanted to understand how it functions more than anything else. I was thinking of it as a gain stage. Thanks for clarifying that.