From rockkey@sbcglobal.net Sat Nov 08 06:41:19 2008
Subject:EL34 147 Leslie Amp mod?

Hi all,

I just posted this on the Hammond list too but I guess Leslies are a
crossover topic. Please let me know what you think...

The power of my 147 is falling off a bit and I'm thinking it's time
for a re-tubing. I like the sound of EL34's and they seem to be alot
cheaper than 6550's (why is that?) so I'd like to try them in my 147
Leslie amp.

I noticed the 122 mod online:

http://www.arcanedevices.com/hammond/122_mod/index.html

and at first, I thought I could use it until I compared the 122 and
147 schematics. I never really did this before but now I notice, for
one thing, the 122 really does not have or need a phase inverter, it
gets both phases right from the GG output transformer so V2 is really
just a driver, right? Cool. Then there's the feedback from the OT
xformer secondary in the 147.

Yeah, there are differences. Has anyone done an EL34 mod to a 147? If
not would anyone like to hazard a guess on how to go about it? I'm not
against adding a negative adjustable bias supply if that would help.
(or would it?)

BTW is the OT the same in both 122 and 147?

Thanks,
Rock