Well, I feel pretty stupid.
Turns out when I had the board out to repair the bad solder joint at the one filter cap I forgot to reinstall the screw for the ground on the board.
Forehead slap.
Works now

Thank you for the help.
I sprayed some deoxit in the pots and Jack's. Seemed to help some but what I notice most is the constant hum goes away when I touch any of the pots. Sounds to me like a ground issue? Bad filter cap?

Very sorry to the group for not ever responding.
I indeed found a bad solder joint at the c27 cap. soldered and amp worked fine.
I stored the amp and never used it until 2 weeks ago. now I have a loud hum when I turn up the treble on the normal channeThe schematic is hard for me to fallow but I am working at it.

otherwise everything works.

Ok.
Last night I had the amp unscrewed from the cabinet and flip upside down so i could see all the piecey parts. I am reading 20v ac out on the transformer. My initial guess is that's too high. No markings to identify. I then put the meter on dc and touched my leads across the supply caps and got 27v?!
The amp actually behaved well and I played through it in this configuration for maybe half an hour. I had won a footswitch on ebay which was why I delayed the test. The hi gain channel switches in and out fine. The reverb was a little less exciting than I had anticipated considering it is a spring type. Was barely noticable.

I do seem to be getting some distortion very easily even on the clean channel. I now wonder if that is due to the high supply voltage?

I do have a good fluke meter but no access to a cro. I will play with it tonight. Looks like some one recently replaced the power transformer. Possibly a misdiag.

Hi,
Yes I got the schematics before I posted here. I need a little help deciphering.

Hi all, new to the forum.
Just picked up a 5210 from 88 and it plays fine for a few minutes then goes into this really loud 60 cycle hum. Its like you have everything cranked all the way up with a single coil plugged in. This can be turned down with the master v. But not the preamp volume. Also cord plugged in or not makes no difference.
To me it seems like the preamp is taking off on its own generating signal or a transistor has latched full on.
Any ideas?

Thanks. I will.

Hello,
I am new here. Just picked up a 5210 that works for a short time and then goes into a 60 cycle hum at full volume. Now the master can be turned down to quiet this to nothing. The pre amp volume does nothing. My understanding of electronics is growing but I am not quite where I would like to be.
It seems to me that something is amiss with the preamp section of the circuit or the transistors have latched on.
I realize this is an old thread. Just thought I would try.

Mike