2. amps-preamps
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Fisher Tube Amp cutting out

I just acquired a Fisher X-101-B integrated tube amp that may have been sitting for some time. It will play for several minutes and than the sound will cut out to a whisper. Turning the unit off for a minute and than turning it back on allows it to reset it's self. It seems to be gaining some time on how long it will run, but still cuts out. All tube light up. Are the electrolitic cans in need of replacement, or will they settle back in given some time if brought on line slowly with a varistat. Or is there something else know to fail on unit of this age.

When it runs, it sounds fantastic! Thanks in advance.

Charlie
charlie8521
3 responses Add your response
charlie8521 OP
5 posts
 
In the of testing the circute with a voltmeter, I found that the unit with come back to life when making contact with the voltmeter probe. This caused me to think that the voltmeter was acting like a small cap.. And it worked best when making contact with the cap. going to the connection point on the unit for testing. Replaced the cap with an off the shelf mylar of similar value, and the unit works great.

I'll wait until I want to go into the unit in bigger way to replace all of the mylar caps. It sounds so good now that I don't want to mess with it. Thank you who provided inputs.

Charlie
charlie8521 OP
5 posts
 
Update. I have also found that when the speakers cut out (or down to a whisper), so does the headphone jack. Sometimes when I tap on the volume control the sound comes back, but will drop out again. Same with a specific 12AX7 tube. But it is not consistent or a repeatable dynamic when tapping on these components. Cleaner has been used on the volume pot.

Charlie
stevecham
3,340 posts
 
Sounds like you could have an internal connection that remains closed until the unit heats up and then something expands and opens the circuit. I had this happen to a Fender tube amp years ago and it took a year to troubleshoot the problem. Time to get out the plastic probe, schematic and meter to check for continuity problems when hot.
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