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FDP Forum / Amp Mods, Repairs, and Projects / Diminished Sound and Slightly Fuzzy

Buckaroo

USA

Apr 11th, 2012 06:18 PM   Edit   Profile   Print Topic   Search Topic

I have an 85 TR 2 combo that worked great last Friday and Saturday night. Sunday night when I turned on the power I got little volume and a distorted sound. Couldn't use it so went an alternate route that night.

Yesterday I tried a spare power tube to no avail. Not sure if I have the tools/knowledge to fix it myself, but I sure could use some sage advice as to what the problem might be.

Thanks.

amphead4

Cincinnati, USA

Apr 12th, 2012 07:37 AM   Edit   Profile   Print Topic   Search Topic

About all you can do without opening it up is substitute all the tubes and also try it through a different speaker cabinet.

Beyond that, it would need electronic troubleshooting to isolate the offensive stage and find any failing parts.

Amps are a lot easier to fix in person than over an Internet forum.

Buckaroo

USA

Apr 12th, 2012 04:48 PM   Edit   Profile   Print Topic   Search Topic

Thanks for your input!

acorkos

SoCal

Apr 13th, 2012 09:30 PM   Edit   Profile   Print Topic   Search Topic

make sure you have the speaker plug inserted into the correct (main) jack and not in the extension speaker jack.

Buckaroo

USA

Apr 14th, 2012 01:26 PM   Edit   Profile   Print Topic   Search Topic

Yes the main speaker jack is being used but I tried it with another speaker and sound is the same.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Apr 15th, 2012 11:10 AM   Edit   Profile   Print Topic   Search Topic

Sounds like a power tube went south on you...

Fire it up in an darkened room and see if the large power tubes are equally lit or if there is something not working.

It would possibly be one tube, but if it is that or more, you'ld need to get 2 minimum or all 4, and buy them matched to replace them as a set!

Buckaroo

USA

Apr 17th, 2012 07:31 PM   Edit   Profile   Print Topic   Search Topic

I have a spare power tube that I swapped out one by one but there was no change. I'll try your suggestion and see what I see. I know they're all working but maybe one or more are working below capacity. Thanks.

pdf64

UK

Apr 18th, 2012 03:07 PM   Edit   Profile   Print Topic   Search Topic

Those are fairly complex amps with lots of tubes and switching jacks.
Try the amp through different speakers and try a different amp through those speakers; I think those are wired to 16 ohms.
Re-seat all the tubes.
Of course you've got a spare known good tube for each type in the amp, so sub each tube in turn, check for improvement and replace if no improvement.
Exercise all jacks several times, squirt in quality contact cleaner first if you've got some; don't forget the fx loop.
Exercise all controls, switches.
If you go through all the above with no improvement, then without test gear and experience, it's time for a pro to take over.
Pete.

Buckaroo

USA

Apr 18th, 2012 07:21 PM   Edit   Profile   Print Topic   Search Topic

I've swapped the tubes with no change. I've also tried a different speaker setup with no change. Next I'll Deoxit the jacks, etc. Afterwards....find a decent repairman. Closest one to my location is about 80 miles away. Thanks for the advice.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Apr 19th, 2012 08:40 AM   Edit   Profile   Print Topic   Search Topic

This may also be the time when a cap and resistor change on the power tubes are needed, with an eye to the phase-inverter tubes.
As the phase-inverter tubes help with the hand-off of the preamp signal to the power tubes.
What I am saying are guesses because I am NOT an amp tech, but these are my best guesses from some experience.
Yes, an amp tech would be able to spot it in a second with a VOM and O-scope...experience!
It is always good to have new power tubes (complete set) because these are the ones that handle the brunt of all the heat and work, the preamp section is not as subject to failure due to the lower heat and voltage duties. The phase-inverter tubes are very much on the high duty list as they have to translate the whole front end to the power tubes.

Best Regards, Woody

Buckaroo

USA

Apr 23rd, 2012 08:20 PM   Edit   Profile   Print Topic   Search Topic

Took out the chasis and sprayed all pots and jacks with Deoxit. Reseated the power tubes. Seems to be working fine now. Due to age and useage, probably wouldn't hurt to have it checked out though by amp tech. Thanks to all the advice.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Apr 25th, 2012 06:59 AM   Edit   Profile   Print Topic   Search Topic

Good to know and you are probably right to get it recapped as the corrosion causing resistance is a sign that heat is building from it and is the enemy!

Glad you tackled that maintenance issue and got it working again! I have been lazy and not addressing that issue for myself....it is a good motivator to hear you resolved something that we should probably do more often than we do!!!

Best Regards, Woody

FDP Forum / Amp Mods, Repairs, and Projects / Diminished Sound and Slightly Fuzzy




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