Peavey Heritage VTX issue

[nosaj]

I have a Peavey Heritage VTX I don't quite understand what is happening.
When it's on high out put tubes look ok, when switched to low output v3 and v4 start to redplate.
Any help would be greatly appreciated. Can't seem to find the hi/low switch on the schematic either.
nosaj
peavey_heritage_vtx.pdf

[g1]

Hi/Lo switch is with standby in HV winding of PT secondary.
Check idle current according to notes in schematic.

[nosaj]

Ok will do but i guess what is confusing me is when it's in HI the tubes seem ok but when Lo v3 and v4 redplate.
The only thing that seems to change is the winding on the PT and C1 in the circuit.
nosaj

[Helmholtz]

Hi/Lo switching is shown with the standby switch in the schematic.
In Lo position only half of the HT winding is used.

Did you check idle currents (see schematic notes "Vi (idle)"?

Edit: Missed posts above.

[glebert]

I would pull the power tubes and check the vi and vk voltages in hi and lo modes. I guess vk would require the power tubes to be in.

[Helmholtz]

I would pull the power tubes and check the vi and vk voltages in hi and lo modes. I guess vk would require the power tubes to be in.

It's a cascode circuit with transistor and tubes wired in series. Pulling tubes interrupts the collector current.
So tubes need to be in for both vi and vk measurements.

I'd start with checking the +/-15V supplies.

[g1]

when Lo v3 and v4 redplate.

Have you swapped V1 & 2 with V3 and 4 to see if the difference is in the tubes or in the circuit?

[nosaj]

Funny you should ask that. I did it and now no more problems. So I'm thinking dirty sockets so need to clean them and look for any arc or leakage on the socket.
nosaj

[g1]

Put them back in their original spots just to be sure.

[nosaj]

Well tubes in any position are fine now. New power supply caps and a power cord with a ground pin. An all is well now.
Thanks all.
nosaj

[nosaj]

Ok problem came back when driving it really hard. But watching the PCB I noticed one of the nuts for the driver transistor had come loose and when it would arc/scratch I could see it and v3 v4 would go blue. Tightened it down can't make it happen anymore now.
nosaj

[Helmholtz]

Did you originally see redplating or blue glow?

[nosaj]

Yes in post 3. It's still holding strong even with some Bass slap which is what would do it before on v3 and V4.
nosaj

[Helmholtz]

Yes in post 3.

Sorry, not clear.
Redplating or blue glow? One has nothing to do with the other.

[nosaj]

Previously before i swapped V3 v4 with v1 v2 it was red plating. it has only done it that once so i cleaned the sockets and pins. The blue glow was related to the nut on the driver transistor being loose.
nosaj