PI input cap values...

[caglej]

Hi Guys,

I was wondering if anyone had experimented with the PI input cap value? I just swapped in a .01 instead of the 0.02 in my non HRM with 6v6's. I have the skyliner stack with a .01 midcap, and the lower value PI input cap seems to help with trimming the bass response a bit. The amp seemed a little farty with the .02 in th PI. I was wondering what you guys have found.....



JC

[Bob-I]

I've tried several values, .02, .01 and even .047. The .02 is the one I stuck with, no farting out and a nice fat tone. I think if I had a 4.7uF bypass cap on OD2 it would be farty, but with a 1uf it's great.

[caglej]

I've been tweaking this amp for the past month, and I'm finally getting the tone where I like it...So far, I'm using 25u,1.5u,5u,5u for the cathode cap values, and .022, .01, and .005 for the coupling cap values. It has the skyliner tonestack with a 300p treble cap, and a .01 midcap. I set the OD input resistance to 235 ohms, and put in the post OD treble bleed........180R and .001u cap to ground..........Also I changed the B+ dropping resistors to get the preamp voltages down between 200-210V. It's getting very close to where I want it to be, but I'm sure I'll find something else to tweak.
Maybe I'll build a 50 watt version with the post OD stack.........

The more I listen to the it with the .01 PI input cap, the more I want to raise it a little........maybe I'll try a .015.......I think Sprague makes this value in the 6PS orange drop series......

JC

[Darkbluemurder]

FWIW, I used lower values such as 0.005 with great results in Fenders which I converted to D-clones.

[pedro]

I keep messing with both 0.01 and 0.022 and like both - it does matter what cathode bypass you use preceeding it/in conjunction though as to whether it gets too farty. As Bob says.
I found 0.02 with 4.7uF "OK", but better with 1Uf or 1.68uF.

Rgds
Pedro