Hi Stewdan . . . I rebuilt one last year and posted about it on this (Fisher) board and described my mods.
Here are the links where I discussed it:
http://www.audiokarma.org/forums/in...4/&q=440A&o=date&c[node]=172&c[user][0]=88202
I won't have time to comment on them for a while but my description should get you started in the right direction. Please note that some of the pics are "before" and some are "after". Also, I removed the wiring which allowed me to check the bias from the top of the chassis because it was creating noise (the yellow wires) but I left the 10 ohm resistors in place on the sockets to I could check from underneath.
I'd also suggest that you start a new thread on this, the Fisher, board about your amp since the title of this thread refers to a different model, albeit erroneously, and the original posts are a couple of years old.
Hi --- Have a few questions after reading your 440A Mods Thread and looking at your pictures:
(1) Is what you are calling the Cathode Bypass Cap actually C93A, the 100MF/100V cap?
And is it the BLUE ELECTROLYTIC CAP in your After Mod Picture?
(2) How did you arrive at 270 Ohms 20W for the Cathode Resistor?
I ask because a 12AX7 is like 84 Ohms and there are Four 12ax7's in the Tuner tied to the Pin in the Tuner Connector.
So, 4 * 84 = ~ 350 Ohms. (I saw something in an Audiokarma Post from another thread, that called out using a 500 Ohm or 550 Ohm resistor which also dropped the voltage on the tubes in the amp.)
(3) Where did you find the 20W power resistors? I can find the cement variety but usually only in 10W size
.
(4) From the After Mod Picture, it looks like you replaced the "Kill Capacitor C106" with 2 Safety Caps in series. C106 was a molded cap 0.01 MF @ 600v, what values did you use for your series safety caps. I can't seem to read what the safety cap says.
(5) How did you connect the CL-80? From the After Mod Picture, it looks like it is across the fuse???? I can't really tell from the picture.
(6) You said you removed the Yellow Wires from the EL84's back to unused Pin Connections on the Tuner Connector because of noise problems.
Were you connected to Pin #2 of the EL84's or Pin #3? I don't think you would have needed resistors for Pin #3 since were would be reading Cathode Voltage and not a drop.
Any answers you could supply would be greatly appreciated.
Thanks
Stew