Cathode bypass (preamp) w/ "blend" pot

[EFK]

I'm sure this is old hat for many, but I was thinking about this as I have a JTM45 open at the moment and an extra hole in the back; I usually like the circuit stock, but sometimes want just a little bit 'more.' I usually find the typical Marshall .68 V2 bypass just a little too much on the 40/50 watt amps, but what if a pot was put in series with the cap (after the cap) so that the bypass effect would maintain similar frequency but to varied extent? I got to thinking about this after I was poking around in one of my Supros and found a -stock- 100 ohm resistor in series with the 35uf power amp cathode bypass cap, paralleling the 250 ohm 10W resistor. Anyway: I'm sure this can be done, my question is, what's a good pot value to start with? No use using a 1M for example if it's only going to be usable for a tiny portion of its range. Anyone try this?

[Dave H]

I'd start with 5k

[EFK]

Thanks for the suggestion! I did indeed try a 5K and it seems to be perfect - by the time I get down to @ 3.5 to 4K or so worth of resistance, I can't tell that it's in the circuit which is what I was really worried about (I wanted to ensure that the amp could still sound 'sans bypass cap' if desired).

[pdf64]

I usually like the circuit stock, but sometimes want just a little bit 'more.' I usually find the typical Marshall .68 V2 bypass just a little too much on the 40/50 watt amps

I find that Merlin's bootstrapped cathode follower arrangement for V2 gives a similar (to cathode bypass) gain boost but without changing the basic tone or overdrive character. Plus it's easy to put on a CTS pull pot switch. Pete.

[EFK]

Why .047 as opposed to .022 or some other value? The bootstrapping looks VERY interesting.