Hello,
Another rookie question. I have a Fisher console amp I've had for about 10 years. Don't play it often as I'm trying to decide what to do with it. Turned the switch one day and it popped the fuse. Got it fired back up and one channel is dead. Took a picture of one of the transformers that looks suspect. I don't know how to test one. Thought I'd ask the smart people before I start searching for a transformer. Thank you
Another rookie question. I have a Fisher console amp I've had for about 10 years. Don't play it often as I'm trying to decide what to do with it. Turned the switch one day and it popped the fuse. Got it fired back up and one channel is dead. Took a picture of one of the transformers that looks suspect. I don't know how to test one. Thought I'd ask the smart people before I start searching for a transformer. Thank you
Attachments
Did you intend to attach the picture?
Before attempting to buy a replacement, note that output transformer failure is usually a symptom of a different kind of failure elsewhere in the amp.
If you have no knowledge of the safety measures which must be taken when troubleshooting valve amplifiers, I suggest you have an expert look at your amp - see the warning notice at the top of the page.
I fat fingered it while editing my post.
It blew the fuse again yesterday. I pulled the amp and I'm going to check the capacitors.
I once had a Fisher console amp in the shop that was pretty toasted.
One output transformer AND the power transformer were shorted, and bad tubes.
It was an SA-16, an EL84 design.
Customer didn't want to invest a lot into it, but agreed that I put in a transistor amp chassis instead at much less cost.
Turned out quite nice too.
One output transformer AND the power transformer were shorted, and bad tubes.
It was an SA-16, an EL84 design.
Customer didn't want to invest a lot into it, but agreed that I put in a transistor amp chassis instead at much less cost.
Turned out quite nice too.
I have the same amp. There's specific things you must do to it, to get it to operate as a stand-alone entity. 1st and foremost, without the tuner-preamp part of the console attached, the cathode current of the output tubes has nowhere to go. Unsure if that would result in the damage you've experienced, with your tubes and output transformer.
I'm fixing mine up so that it operates normally by itself. I'm going to try generating a bias voltage, applying it to the existing bias control for the output tubes. At the same time, I'm going to reduce the output tubes screen voltage, as this amp will run a very hot B+ without the rest of the console circuitry attached.
You'll need to measure the windings on that suspect transformer, compare to the other channel. If its cooked / shorted, then you'll need to make a decision, something along the lines of $50 for another OPT, $50 for set of working 6BQ5 tubes (or equivalent...); $50 for a matching OPT - after you get it working / stable with the mis-matched ones.
Even with the shorted OPT, you could sell it on ebay "as-is". "for parts only" and probably still get as much as it would cost to properly fix - given the worst case of that OPT you pictured being measured shorted. Even with its faults fully disclosed.
I'm fixing mine up so that it operates normally by itself. I'm going to try generating a bias voltage, applying it to the existing bias control for the output tubes. At the same time, I'm going to reduce the output tubes screen voltage, as this amp will run a very hot B+ without the rest of the console circuitry attached.
You'll need to measure the windings on that suspect transformer, compare to the other channel. If its cooked / shorted, then you'll need to make a decision, something along the lines of $50 for another OPT, $50 for set of working 6BQ5 tubes (or equivalent...); $50 for a matching OPT - after you get it working / stable with the mis-matched ones.
Even with the shorted OPT, you could sell it on ebay "as-is". "for parts only" and probably still get as much as it would cost to properly fix - given the worst case of that OPT you pictured being measured shorted. Even with its faults fully disclosed.
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You can test the tubes, but don't know how to test a transformer?
Now I wonder whether you're as "rookie" as you led me to believe you were! 😀
I have a couple tube testers. so it's pretty easy. I have refurbed a couple amps by changing the capacitors and resistors and some polishing. I've checked the voltage on transformers in the past, but I don't know how to implement it in the diagnosis. I consider myself a rookie.
I was originally going to suggest what jjasniew has already suggested, but decided to err on the side of caution.
To be specific, measure the dc resistances of the primary and secondary windings of the suspect output transformer and compare the readings with those obtained from the transformer on the working channel.
The transformer was shorted. After searching and waiting to find a mate, I had Transcendar rewind it, replaced the electrolytic capacitors and put some good testing tubes from a Hammond organ I salvaged. Running smooth.
It's been a long time since you started this thread, but I'm glad to hear that you found a resolution to your problem.
Thank you. I've been looking for a transformer without having to buy a whole amp and happened upon Transcendar that was reasonably priced in comparison.
