Variable cathode resistor

[mooreamps]

"Mooreamps" on the forum has a power scaling method where he varies the screen resistor. If that works, I guess varying the cathode resistor might work too.

But my feeling is that the screen resistor will give better sounding distortion at low power, because the clipping will still be quite symmetrical.

If you use a high value cathode resistor, the tube can turn ON a lot further than it can turn off, and that will make the clipping very asymmetrical.

The other method I've seen, where on a self biased SE power amp, they put the cathode resistor bypass cap on a switch, which is more inline with using the variable cathode resistor setup as described above. but no, I do not actually "vary" the screen resistor. That in itself is not power scaling. But this video clip is power scaling, and I want to see if this is what he is looking for.


http://www.youtube.com/watch?v=gq-pn-LlQM4&feature=related





-g

[Rutger]

Well, switching out the bypas-cap wouldn't give you that much gainloss. It would be a help but I think you should combine it with other things.

When you vary the screen resistor you would probably have too much side-effects you don't want to hear/feel.

Very nice clip indeed, sounds great!

[tedmich]

old thread but I thought I'd share my enlightenment, the venerable Peavey Rockmaster preamp uses a 0.1uF in front of a 10k pot wired as a variable resistor to ground from the cathode of V1B as a "presence circuit"


which normally would be implemented with NFB in a "real" amp

also here is a cute (and somewhat sonically meaningful) logo for the old guy

[mooreamps]

When you vary the screen resistor you would probably have too much side-effects you don't want to hear/feel.

Very nice clip indeed, sounds great!

Thank you..... Quite personally, I think my power brake tends to work like a charm. When I do the upgrade to my video camera, I hope to upload more decent sounding video clips....

-g

[ElectroTerr]

I made a 8056 Nuvistor preamp w a 6 position rotary so the bias could be moved down toward shut off.As the bias got more and more negative the sound got duller, less hot sounding. So the distortion was just blah, even tho there was more of it.