VHT Pitbull 45 Cuts Out

[nosaj]

nosaj

[g1]

just about every EL84 I put in it is red plating at this point?

In post #33 your pin2 voltages were inconsistent and low. Your bias voltage at pin2's should probably be around -15V. If it is not enough the tubes will red-plate.
You do not need the power tubes installed to deal with this issue.

[ca7922303]

In post #33 your pin2 voltages were inconsistent and low. Your bias voltage at pin2's should probably be around -15V. If it is not enough the tubes will red-plate.
You do not need the power tubes installed to deal with this issue.

Think I found the issue. Resoldered 5w 390R resistor, now all pin #2s(16.9vdc)
B+(422vdc)
All pin #9s(410vdc)
Calculating (20mA)
(8.5 watts)
(70%) disapation
No replating, have four(4) Sovtek EL84s, so far holding up to the (422vdc).
All power tubes in in the 325-350°F range. This is with no signal.

[g1]

The 390R should not have anything to do with the -17V bias voltage at pin2's of power tubes.
It's possible there is another bad solder connection somewhere in the line from the bias (-) supply. The fault may come back again so you should probably tap around with a chopstick to see if you can get it to come back.

[ca7922303]

The 390R should not have anything to do with the -17V bias voltage at pin2's of power tubes.
It's possible there is another bad solder connection somewhere in the line from the bias (-) supply. The fault may come back again so you should probably tap around with a chopstick to see if you can get it to come back.

Chopsticked everywhere, all seems good. At (422v B+) and (20mA idle current), with a 1000hz/.20v sine signal I'm getting (21vac @ speaker output) That's 55 watts if my math is correct. If correct, that would be 10 more watts than amp is rated at. Gonna let buddy take it on a gig again. Maybe it won't blow another mains fuse after three chords this time. Thanks for the help. Also, all EL84s are holding at 350-370°F and of course no red plating.

[nosaj]

Put an Mp3 player into the input and let it work for a few hours, if you can't handle the noise use a dummy load. Then you won't look foolish if it fails after 3 chords.
nosaj

[ca7922303]

Tested with volume at 12:00 for about an hour and all's good so far. All EK84s are staying under 370°F and no red plating. Owner of amp likes it and says it seems to have more clean headroom now. It's going to a gig tonight, so I'll post how it turns out.

[ca7922303]

Gig was a success. Amp ran nonstop for 3 hours straight without any issues, sounded great and was able to touch back of chassis without burns. He's running 4-Siovtek EL84s @ 422vdc. I advised owner that he would be better off if he used 7189s or at least JJ EL84s, but for now, Sovteks are holding up. Appreciate all the help.