Peavey VTM 120 Issues

[TigerAmps]

I have a Peavey VTM 120 with a problem power transformer.
At the filament voltage connector I measure 6.0V and with 2 6L6 power tubes and the 4 12ax7's the voltage drops to
5V at the last 12AX7 in the chain (furthest from the power supply board). The Molex connection are good and tight.
Another symptom is that at idle, the power tubes look OK; however with signal, one of the 2 tubes starts to red plate
(I only installed 2 of the 4 6L6's for testing). Bias voltage is -54V (at idle before signal is applied).
I re-capped the power supply board and the middle board with the 12AX7's. There is no burnt smell from the transformer.
Also, the high voltage is around 480V on the plates with a standard line voltage of 117V to 120V which seems a little low.

During testing, I get signal out of the send but it seems weak (guessing the low filament voltage on that side of the board).
Signal into the return, produces faint output at the speaker jacks. Signal into the regular input results in the red plating.
It seems like running signal thru the entire amp results in the red plating.

I believe the PT is faulty. Any thoughts?

A rewind will cost upwards to $200.00 with shipping which is not cost effective.

PT replacement idea: Thinking about using a Marshall JCM 800 PT for the B+, filaments and bias (building the appropriate circuit)
however, I would need to change the LED's/lamps or use a 2nd transformer (36V CT 18-018) to power the existing bias/LED circuit.
I measure 40V CT (20-0-20) on the orange wires on the original PT which appears to be correct.

Has anyone done anything like this? Any suggestions?

[Enzo]

I sincerely doubt the transformer is bad.

Molex may be tight, but that is not the same as making good contact. Is there any browning on the molex housings?

The two yellow wires from the transformer have 6v on them, but the voltage sags at the other end? Then the transformer is doing its job making 6v.

Those yellow wires have their molex onto the power board. Do those pins look gray and like they got hot? That 6v goes through teh 8A fuse and directly to a four pin ribbon over to the main board. Those four pin ribbons burn up, so is there any browning on the two pins with the 6v on them at either end?

The 6v then crosses through the main board to an 8-pin ribbon over to the power tube board, again the two end pins carry the 6v, any browning showing? In all ribbon cases pull the connector off and look at the pins, any sign of having been hot?

Those ribbons are a weak link, and the usual solution is to just hard wire where the ribbons used to be.


480v B+ is just fine.

Try the other two 6L6s instead of this pair, does one red plate in that pair also? If so is it always the same socket, or does it move with the tube?

[TigerAmps]

Enzo - Sorry for the delay in response ... The amp was starting to get to me, so I sidelined it for a little bit. Finally got back to it with a fresh start and an open mind.

So - Re-checked all the voltages and found a bad plate resistor on V1; then I pulled the middle board and completely check every resistor and cap.
Put in 4 different good old made in the USA 6L6GC's and no red plating; I thought I was out of the woods, but NO!
The volume was still very low - Silly me - I used 4 brand new Sovtek 12AX7LPS tubes.
So I pulled out 4 old RCA 12AX7A's - plugged them in and low and behold - real significant volume.
One of the new Sovtek's was bad (found by replacing the RCA's one at a time).
I still have a few issues to work out but at least it is now up and running.

Thanks for the advice ...