SF Deluxe Rev:cathode bias switch help?

[Zouto]

Hi,
I want to change my SF Deluxe Reveb to switchable cathode bias as in
http://www.londonpower.com/cath-fix.htm.
Has anyone tried this mod, is it reliable, how does it sound?
Any help, hints, wiring diagrams much appreciated
Zouto

[cbarrow7625]

I did this in my 4 x 12AU7 output stage amp. I like it quite a lot. I actually went one step further and made it so I could run one tube on fixed bias and one on cathode bias (as well as full cathode or full fixed).

I find myself using it on the inbetween position most of the time because it gives me a best-of-both-worlds sound and feel. To do that I needed to use seperate cathode resistors / caps for each tube pair (something I would have done anyway) and used a 3 position rotary switch (doubling up contacts for additional current carrying capability).


It is reliable in my amp, however mine is only about 14 Watts. Will you like the sound? I don't know. I like the way it sounds when I am trying to get a vintage sound but I prefer the fixed bias when I have the hi gain channel selected. The cathode bias can get a littel mushy and indistinct with high gain.

Sorry, not diagrams here. Kevin's drawing is pretty good, I owuld use that.

Good luck,

Chris