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In Reply to: RE: How did you narrow the problem down to couling cap(s)? posted by FenderLover on July 08, 2014 at 19:05:41
Good question, FenderLover. I am not sure it is the coupling caps at all. Bad answer, I know, yet I don't have the proper equipment to test, and this is just an educated guess.
Idle bias was at 230mA, although now reads 0mA no matter where the dial is adjusted. The bias output now also reads ~24mV and ~16 Ohms no matter where the adjustment dial is placed, whereas typically the mV can be adjusted.
Thanks much for any insights on how to troubleshoot!
Kind regards,
Michael
Follow Ups:
Hi, I'm trying to understand your problem.Can you tell me what is meant by, "The bias output now also reads ~24mV and ~16 Ohms no matter where the adjustment dial is placed, whereas typically the mV can be adjusted."?
Thank you.
You said "one just started eating the 0.5A tube fuse within 5-10 sec of power up. "
Here the thing, I don't think the power tubes have even started to conduct in 10 sec. I think they have a longer warm up time than that.
Something is drawing to much current through the .5amp B+ fuse and I don't think it could be an over biased output tube caused by a leaky coupling cap because I don't think the output tube's cathode is heated up enough after just 10 sec for the tube to conduct.
That fuse is probably between the power supply and the output transformer's primary center tap.
If that fuse is blowing within 10 sec then it almost has to be a shorted output transformer.
Have you tried turning on the amp without the output tubes installed?
If the fuse stills blows I think all that leaves is the output transformer.
I wish I could see a schematic.
Caution, the B+ voltage will be higher than normal when the output tubes are pulled. Don't shock yourself!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/10/14 07/10/14
One that is familiar with your product will help.
Good luck with the unit!
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