Plate and Cathode Resistors scaling

[roberto]

We are used to see this in dumble amps:
100k 1k5 - 120k 1k8 - 150k 2k2 - 180k 2k7 - 220k 3k3 and so on..
It's something I use in other amps, expecially in the cold stage.

Have someone ever tryed this approach with three trainwrecks stages?

[rooster]

Roberto - Hey, not to change the subject but did you get the tritonaudio 9 pin socket installed? Did you get my silicone rubber cushion? ??? How does it work for you? I never heard anything from you on this....

As to the cathode resistors, not a Dumble guy here. I had no idea he had a little formula going on there. Interesting.

[roberto]

Hi rooster! here you are. Thanks for all, really, and sorry for my late.
I simply can't find the old thread with infos about cushions. I've done some experimentation with it and others, and also in high gain it gives more stability. Very useful and cheap gadget on V1.

As for the plate and cathode scaling, you can calculate the gain with this software: http://amps.zugster.net/tools/triode-calculator
then scale up and down to fit tastes but with the same gain (EG 100k and 10k, 47k and 4k7, 33k and 3k3 and so on). scaling up you have more harmonics, scaling down you have more dynamic and crunchy saturations.

[roberto]

About Rp and Rk scaling, I've done this frequency analysis.

As you can see, scaling Rp and Rk so that Rp/Rk will be pretty constant, not only has a very similar gain, but also a similar "bypassed/unbypassed cathode" gain shape.

This is the starting point of this thread, and what I use for toneshaping. Obviously it also depends on how every stage goes into saturation..

[RJ Guitars]

I am trying to figure out if this has something to offer for the lower voltage lower wattage amps I am building? I built an amp with a pretty low voltage transformer and then had to drop the value of the plate resistor to bring it back up to a reasonable value. I didn't change the cathode resistor, do you think I need to?

thanks,

rj