Peavey Triumph cuts out until it warms up.

[stoneattic]

I have a Triumph 60 combo that when first turned on will work for about a minute or two, then get really (barely audible) quiet, then start working again after another minute or two. It will repeat this cycle 2-3 times until it's warmed up and then be fine playing for hours. I've noticed that when it does this, if I go to standby, then back, the volume returns.

Other than generically looking for bad solder joint, checking and cleaning connections and re-tensioning the tube sockets, any ideas?

TIA!

[stokes]

Filter caps and or tubes.

[stoneattic]

Thanks for the reply. I've looked inside and none of the caps seem obviously bad (leaking, bulged, etc). I have plenty of 12AX7s around and I think I have a 12AT7 but no 6L6s. Do you think it would be more likely power or preamp tubes?

[Jazz P Bass]

I can't think of a pat answer to give you.
It sounds like some fault checking is in order.
Try to narrow down What is failing.
Is it a power supply voltage problem or a signal loss problem.
Things to monitor as it is acting up.
The power supply B+ voltage.
The bias voltage.
The signal path.
After you identify in which way the amp is failing, then we talk why.
Happy Hunting.

[Gtr_tech]

Watch the output tube (the big ones) heaters as the sound dies off....does the heater in those tubes get dim or go out completely? PV tube amps from that era have a reputation for frying the connectors for the tube heaters. If thats the case you should have that repaired before it flames out and the damage is more extensive.

[Enzo]

And while bulging caps are certainly bad, good looking caps are not always good. You often hear at their funerals, "Oh, it looks so life-like."

[stoneattic]

I only had a couple of minutes to mess with it this weekend and figured I would try to narrow the problem down.

I plugged into the Triumph and took the "preamp out" into the "power amp in" on another amp. It did the same cut-out trick so I figured it was something with the preamp.

But to verify my experiment was valid I plugged into another amp and took the the "preamp out" of that amp into the effects return (since the Triumph doesn't have a "power amp in") and it did the same thing. This has me kind of stumped since it seems like the problem may be amp-wide. My first thought there was something with the tube heaters but the tubes are all still lit when this happens.

I guess I need to poke around for bad solder joints next.

[Jazz P Bass]

Run a known good cable from the effects send right back into effects return.
This is before preamp out.
If the jack is not closing right, this will prove that point out.
Attached is the schematic.
I would look real close at the Molex connector for the heater voltage.

John G.

[stoneattic]

Originally Posted by Jazz P Bass

Run a known good cable from the effects send right back into effects return.
This is before preamp out.
If the jack is not closing right, this will prove that point out.
Attached is the schematic.
I would look real close at the Molex connector for the heater voltage.

John G.

Thanks. I'll try jumping over the effects loop, but since the tubes were still lit when the problem was occurring, wouldn't you think they were getting heater voltage?

[Jazz P Bass]

Look at the picture that I attached.
The problem looks like it is in the 12AT7 circuit shown.
If Preamp out is a bad signal & Eff Return is also a bad signal, it leads to this tube, tube circuit.

[Gtr_tech]

What about the effects send? Did you patch that into another amp and see if that signal stayed around? Thats before the 12at stage.

[stoneattic]

When I got home from work I tried the following:

1) Replaced the 12AT7 - no difference, same issue.

2) Jumped the effects send to the effects return - no difference, same issue.

3) Jumped from the Triumph's effects send to the return on anther amp, had to plug a dummy cable into the effects return of the Triumph to kill the signal to the Triumph's power amp - no difference, same issue.

It's too late to dig into it now, but when I get a chance I will check the heater connector as suggested, but all the tubes stay lit when the signal goes away, so I don't believe that's the problem (but I'm newb and have been wrong more than once). I will take a good look at the circuit around the 12AT7 as well.

The thing that I keep thinking is the clue is that switching to standby creates a pop, then going back off standby gets the volume back. This works even if I flick the switch quickly.

[Jazz P Bass]

Well I must admit that I did not process the fact that the standby switch effects it.
That should have nothing to do with the heaters.
Jumper the switch?
I really think you need to monitor some things to see just exactly what is acting up.
B+ for one.
Break out the DVM.

[Enzo]

I doubt it is the switch, but the suggestion is valid. Jumper across the switch with a clip wire. It seems that when the amp is in standby - with the high voltage off basically - and then you turn it on, it works untikl something chargers up and squeezes the signal out. I don't think it is the switch itself, I think it is the application of high voltage.

Of course that could be wrong. A jumper across the swsitch will tell you instantly.

SO if the preamp out fails, let's chase that down. When it fades away, check the plate voltages on the small tubes. Present or not present?

[stoneattic]

I didn't get a chance to check anything today, but I took some pics so that I can remember how to put it back together and noticed that the tops of the filter caps are bulging, but I can't tell if that's normal. The tops are plastic, which I've never seen (or at least noticed before) and when I push on them they deflect easily. When I've seen bulged caps before the bulged area is firm. Is this normal?

[Enzo]

Probably OK. What matters is the cap can itself. if that is bulged up, the cap is bad. But yours looks like the very common warped plastic cover. SLice the plastic sleeve enough to pop those warped discs off the top to expose the aluminum can end. if the can end is flat, you are probably looking at good caps. Dont; bother trying to return the plastic cover.

[bfglp]

hey, i just found this site doing a search to find info on the problem with my triumph. and i have the same issue with my 60 watt combo.

the last thing that happening to mine is that it will go back to full volume when i go to the ultra gain channel for a second as well as hitting the standby.

please let me know what you find
thanks
bill