Peavey Triple X trouble

[studiotech]

First post here. Hello to all!

I've got a triple X on my bench right now. Customer states that they lost majority of power intermittently a few times and replaced power tubes. Worked for a few weeks and now nearly dead. Basically I've got to turn her all the way up to get a little crackle of sound.

So far, I've checked all tubes as good and swapped with another set just in case. Same results both times. EFX send signal is clean at the rear jack. LINE OUT has the same distorted crackle as the speaker output which makes sense since it is the same feed. Plate and heater voltages are good and present at each tube socket. Signal is clean into the power amp board and in and out of the 12AX7 located on the power amp board. The customer states that prior to the problems, they had been running the amp at full, max volume for several months. Deaf much? I've already resoldered all tube socket contacts and all ribbon connections on the power amp board. I'm beginning to suspect that they have killed the output transformer. Anyone got other ideas for me? Thank you.

Greg Begland

[Jazz P Bass]

Run a jumper from FX Send to FX Return to rule out a bad contact.

[studiotech]

Run a jumper from FX Send to FX Return to rule out a bad contact.

Been there, done that, but forgot to mention it. Thank you. Anything else? As mentioned, low level signal is strong and clear all the way to the power amp section, but comes back from the output transformer VERY quite and VERY distorted. I'm used to getting nothing if a transformer dies, so that's why I am unsure that it really IS the output transformer.

Greg

[Enzo]

You have strong signal at the plates of the phase inverter? And it is also at the grids of the power tubes? How much signal is on the plates of the power tubes?

You said you have B+ on the power tube plates, but no mention of the screens, they are equally important to have B+.

Have you switched the speaker impedance switch to other positions? Try it, it won;t hurt the amp to be on the "wrong" impedance.


How much signal is present at the WIRES leaving the OT, not the jacks. Those wires come into the jack board on a connector that may have failed.

I'm used to getting nothing if a transformer dies,

Like any other part, transformers can fail in many ways.


Transformers do fail, but they are way down the list. But go over to RG's Geofex web site and find his very simple transformer tester. Make one and try it.

[soundguruman]

Well the last one I worked on:
1. R84, in series with power line input, had crapped out, and the traces on the board TO it were burned. Fixed the bad traces and replaced R84.
2. 1 burned 8 pin tube socket, replaced it.
3. 1 Bad screen resistor, replaced it.
4. R121,R122 were arcing burning to screen resistor, R117. Replaced 121 and 122, moved them to opposite side of circuit board. This may prevent further arcing.
5. Phase inverter tube was bad. 1 Power Tube was bad.

Remove and inspect power amp board. Check for damaged traces, or signs of burning & arcing.

Well - anytime you have transistors in a tube amp, you might suspect that one has failed...

Anytime you have mechanical relays in an amp, you may suspect that the contacts have worn out, and your audio path is interrupted...

"besides" the usual...cracked soldering on input jacks, cracked solder on controls...
or bad jacks, switches in jack are no longer closing, interrupting audio path...

peavey xxx.pdf

But after I did all that, it worked OK again.

Peavey 601 483 5365
If you need sockets, R84, etc...the price is fair.

[Mick Bailey]

I'm used to getting nothing if a transformer dies, so that's why I am unsure that it really IS the output transformer.Greg

A shorted OT turn will often cause a distorted, low volume output. I'm seeing a lot more these days.

[soundguruman]

But it could be other stuff...

[Mick Bailey]

I know, just saying that a defective OT doesn't necessarily mean you get nothing out.

[studiotech]

Thank you Enzo for the hints. I moved the speaker impedance switch previously. No change.

Yes, I do have approx 500V on the plates as well, I forgot to mention. I have not measured signal level with an O'scope. I'm just using a cheap, homemade listening probe. Signal is very strong to the inverter and onto the power tubes. Even down into the output transformer, I have a strong, clean signal. No distortion or crackle on the clean channel at all.

I have not measured the output of the transformer wires, but I did remove, inspect and re-seat the output connector that feeds the jack board coming from the transformer. All appeared to be fine and the solder points on the board were resoldered as well. I will take some more measurements and return with results.

[Enzo]

Power off. PLug a cord into the speaker out jack and select some impedance, don;t care which. At the free end of the cord measuer resistance tip to sleeve. We are looking for continuity through the OT secondary... or not.

[studiotech]

Power off. PLug a cord into the speaker out jack and select some impedance, don;t care which. At the free end of the cord measuer resistance tip to sleeve. We are looking for continuity through the OT secondary... or not.

Well, that makes too much sense. Sure thing. Will do next time I'm in the shop.

Greg