Amp fading out!

Hi everyone.
Still problems with my old fender.
this time after 30-40 minutes of playing it started to have some volume losses, and finally it became really harsh sounding and low-volume, then at this point I turned it off (after visually checking the power tubes and they still looked ok, no plate glowing, just their normal orange light).
i hope this is not connected with the fact that when my band and I last rehearsed two days ago we had to stop because of a black-out; I had not played the amp till today when the problem occurred.
please tell me it's not a transformer... :cry:

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I doubt if the power cut caused this problem; more likely that's a coincidence. This sounds like either a problem with the amp's power supply or the 6L6 (or are they 6V6?) power tubes. Please remind me of your Fender amp model.

Are the valves quite old? They don't have to be redplating, they could just be worn out. If there is not much getter flashing (the silvery substance on the glass envelope) then they're at the end of their useful life.

A power supply problem doesn't have to be the transformer - it could be one or more of the filter capacitors. I'd suggest you take the back panel off the amp (don't touch anything) and play while watching in a darkened room. Stop immediately if there is any arc-sparking in the transformer. I suspect the power valves are the problem, though.

Hi bass,
first of all it's a BF bandmaster head, with 6L6 tubes.
the power tubes are quite new (well, nearly a year old now) but maybe they just been through some hard beating due to a resistor being nearly dead (don't know the exact name, it was a 470ohm resistor crossing one valve base, I replaced it a month ago). the filter caps were replaced three months ago, it should not be that but who knows? anyway after the capacitor replacement a lot of hum and noises disappeared, so the new ones seemed to work. could it be dead tone circuit condensers?

I looked for some info on the internet, next week I'll try to check if any of the preamp tubes does not light up or something like that.
when I last played the amp two days ago there did not seem to be any sparkling anywhere but I do not know it there was anything going on in the inside of it.
it might even be a dead solder joint, after all this is a 42 years old amp.
anyway next week I'll check if the joints are ok, and leave the results here.
thanks for now! have a nice weekend.

Riz, I suggest you search for Plexi Palace - the vintage amps forum. They have a Fender category. A lot of experts will be able to help you out. Here, I'm no expert but I try my best. PP will be very useful to you.

Hey Riz,

My Fender Deluxe had the same symptoms, turned out to be a preamp tube. sb

HUH, forgot to update this topic.
in the end I opened back the amp, checked the solder joints across the tubes, and guess what? the resistor I had replaced on one socket was not soldered right, and the equivalent resistor on the other socket was nearly gone too, this is why when hot the amp started fading.
replaced that one as well, controlled again the joints, eveything works fine now.
AFTER doing this job, found this site called hoffmanamps.com
which is full of useful information about taking old fenders back into shape. If only I had found these pages before...
anyway, to any novice out there: be careful using spray contact cleaner...

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