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RE: low 12AX7 filament voltage in my Fisher X-100-A amp

Posted by microbe (A) on December 5, 2016 at 19:59:10

In Reply to: RE: low 12AX7 filament voltage in my Fisher X-100-A amp posted by Jim McShane on December 3, 2016 at 12:27:50:

Hi Jim,

Been out of town...thanks for the response. I did try bypassing the 22 ohm resistor with a jumper wire and now I'm getting about 11 volts dropping across the filaments and all of the 12AX7's appear to be conducting properly. The conduction problem on one of the tubes may actually be due to oxidized pins on the tube socket; sometimes it works, sometimes it doesn't. I'll hit it with some deoxit. If I were going to hang onto this amp, I'd definitely consider doing the mods you've suggested (maybe I should do them anyway). My plan is to pass this onto my cousin; she expressed an interest in owning a vintage integrated tube amp. I liked this one because it doesn't require any bias adjustment, just plug and play. I've changed out all of the electrolytics and coupling caps and inserted a couple of thermisters to get the voltages down to spec. Also retubed it with brand new tubes (I purchased them from you a while back, thank you very much!). So hopefully this thing will behave itself and give her years of trouble-free service. Thanks again for your help.

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