Tuuuubes?

[veteransdaypoppy]

So I've got a Fender Twin Reverb and it uses 4 6L6 tubes. It's old as methusela (thinkin late seventies early eighties?) and I doubt anything on it has ever been replaced. It was my father's and now it's mine. I want to fix it up.

I'll preface this by saying that I know absolutely nothing about tube amplifiers because I've only used the amp a few times when I was about 15 and a spoiled brat and I really just abused the hell out of the amp. Nothing too bad, I just didn't use the standby switch and all that jazz. Now I've got a Marshall MF350 that I use practically all the time as a half stack. Solid state but I actually like the tone and it plays real friendly with my pedalboard.

Now I have no idea what a bad tube looks like and I don't actually have a functional camera on me right now so I'll just explain what happens. If pictures are important I'll scrounge around for a camera and take a few shots. I'd actually like to find out what it's worth at some point anyway, so... Here goes!

*The first big problem is that when I turn the amp on, as I turn the treble up (either on the vibrato or the normal inputs) a hum gets louder. So if the treble is on 5, it hums loud. 10, unbearably loud, etc. (Tube issue?)
*Second issue is that some of the pots are crackly. I know that this is an easy fix (just spray something in there?) but I'm not sure exactly what I'm supposed to use, or where to spray.
*Third, when is it time to replace tubes? When I turn the amp on, the tubes do glow red on the top of them and they get very, very hot. On one side of all four tubes there is a big gray spot on the glass that doesn't look very good.
*Fourth, The reverb/vibrato(which is actually tremolo) footswitch is very tempermental. I replaced the RCA jacks on the end and no dice. Should I replace the switches?

I've heard that changing some capacitors is actually good for an amp too, but often unnecessary.

I love the sound of this amp and I want to be able to use it, but it's just unbearable right now. If you guys can tell me anything that a complete and total worthless n00blar to tubeage should know I'd be very grateful and handjobs to all.

Thanks in advance (and sorry for the length)

[metalmariachi]

Ah ha now you're in my world.
I just happen to repair tube amps for a living.


The Hum is probably due to old filter caps. Big honking electrolytics.
They are under the can on the chassis.
Also there are some 25 uf 25 v on the component board and 2x 50, or 100 uf 75 v caps on the rectifier board for bias filtering.
Those should be changed too.
That is what people are talking about when they say replace old caps.


Scratchy pots, just get a can of contact cleaner at R-Shack and spray them out.

Tubes can and often do last forever you can't tell by looking,
You have out put and sound so they are working, but should be checked for microphonics and output with a tester.
After the cap change the bias should be re set as the voltages will come back up a bit, or a lot depending on how bad the caps are.

Foot switch may be the switches, probably is, but could also be loose wiring inside.
Switches are cheep and easy to swap.

Is there a good tech in your area? Where are you located btw?

PM me ,

MM

[bigchiefbc]

Ah ha now you're in my world.
I just happen to repair tube amps for a living.

PM me ,

MM

MM, I'm sending you a PM about my amp as well.

[metalmariachi]

got 'em and pm'd back.

MM