Peavey Heritage VTX blows cathode drive transistors

[booj]

peavey-heritage-vtx.pdf

I replaced the output tubes since the fault ate up one of the old set. first I tried an MJ15024 for one of the drivers which lasted several hours. The same transistor blew. Then I bought a new set of 6465's from CE dist. (the "proper" transistor) and replaced both of the drivers. This time the amp lasted about two minutes. All surrounding parts look good. I don't think the tubes are at fault, since they all draw about equal current in my cheap a$$ tube checker. I told the customer I'd buy back the tubes and give him his labor money back. He agreed to take the loss on the drivers for taking a shot at it. I'm giving up on this unless someone can come up with something to try. It's a weird circuit. The tubes have to be in and the amp has to be operating in order to measure any operating voltages. Thanks for your time!

[Jazz P Bass]

Well let's start with this.
Do you have 0.522 Vdc on the base of Q7 & Q9?
There are a slew of voltages labeled on the schematic.
Do all of the voltages stated in the output driver section agree with observation & the schematic?
Are all off the resistors between Q6 through Q9 intact & terminated properly?
Something has to be off.

[booj]

Got it fixed. I decided to just pull all the caps and semiconductors out and replace them. I had gotten as far as replacing all the e-caps, and pulled the pre-driver transistors, Q6 and Q8. One of them was leaky. Of course that didn't show up in a resistance check while they were in circuit. This post is for those who like to know how a repair turned out.