My Model T died today..need suggestions to fix it.

[Thatbassguy]

I drug out my old (Ver. 1) Model T today.  After it warms up I take it off standby.  It has low distorted volume than fades away to nothing.  I let it set and some times it will start playing at normal volume
then suddenly loose volume and become distorted again.  It will eventually die off to no sound at all.

The amp has been sitting unused for at least 5 years.  I have had it serviced/repaired in the past.  It now runs KT88's. I gigged with it  until about 5 years ago when I got a lighter Ampeg head.

Any ideas?  Before I call amp tech/

Dave

[EdBass]

It could be a lot of things, but my first step would be to check the filter caps. It probably just needs to go to a tech for a checkup.

[Thatbassguy]

Thanks for the reply.    I was hoping it would be something simple but probably not.  I haven't worked for 7 months now so I won't be having it fixed unless its something simple.  I have 4 or 5 other amps that I can use as a back up to my Ampeg.  I think my (Ver.2) Model T is still in working order.  I'll try it out in a few days.

Thanks again for the reply,

Dave

[soberskipper]

Thanks for the reply.    I was hoping it would be something simple but probably not.  I haven't worked for 7 months now so I won't be having it fixed unless its something simple.  I have 4 or 5 other amps that I can use as a back up to my Ampeg.  I think my (Ver.2) Model T is still in working order.  I'll try it out in a few days.

Thanks again for the reply,

Dave

If you live in north florida and want to come by, i will do the electrolytics for free. I think it cost me something redicilous like $19 to do the caps in my model T. That symptom sounds more like a power component like a resistor in the B+ drops but whatever. Most times, an amp that needs filter caps really bad will just hum really bad. The great thing about a model t is that the problem HAS to be simple!! there are only a handfull of components in there, its basically a bassman. Anyway, offer stands!

[loudthud]

Working inside a tube amp is dangerous and could result in serious injury or death. Don't attempt if you don't have experience with electronic repairs or a mentor to look over your shoulder.

In the absence of hum or loud poping, a preamp problem is suspect. Remove the preamp tube shields and check that you can see the two orange glowing spots inside each preamp tube when the amp is on. If that's ok the next thing to do would be spray the pots and preamp tube sockets with De-Oxit. If you don't know how to do this, take the amp to someone who does.

[Thatbassguy]

I got the amp working again today.  I cleaned the tube pins and sockets.  I will replace 1 of the 12AX7's.  It doesn't have as bright of a filement as the other 2 do. It is also a different brand.  I do have  few old Amperex 7025's that I may use.  I stashed them away years ago.

Thanks for the tune up tips,

Dave

[Thatbassguy]

Well the amp fried tonight after I changed out 1 of the preamp tubes. I was trying to put the chassis back in the cabinet when something popped and I saw smoke.  It's dead now.

Time to call my amp tech......

[loudthud]

An amp should not only be turned off when you install it in the head box, it should be unplugged!!!

[Thatbassguy]

It was just a popped diode.  All is good again!

[EdBass]

It was just a popped diode.  All is good again!

IMO that's one of the biggest attributes of hand wired amps. Unlike most mass produced PCB pieces; particularly the current ultra inexpensive Asian dip soldered crap, the handwired gear never becomes "garbage".
You can theoretically maintain and repair them forever; no flimsy, proprietary and unobtainable after a few years PCBs to fail and render the amp worthless scrap.

[jaywalker]

I drug out my old (Ver. 1) Model T today... 
The amp has been sitting unused for at least 5 years.

Best to turn amps on every once in a while to keep the caps charged up. They can become petulant if ignored for long periods of time.