Peavey Classic VTX output issues

[Tone Meister]

Have a Peavey Classic VTX in here with a couple of issues. Power tubes were shot, so I changed power tubes and two known-good sets are drawing very low current. One socket exhibits an issue when the tube is moved slightly the amp makes a hideous buzz that sounds much like DC on the output of a solid state amp.

The R126 and R130 5W/5k6 resistors test ok. The R113 and R114 1k5 resistors test ok. All fuses are ok.

Plugged a cable into the POWER AMP IN and measure no appreciable DC (0.003v)

Here are some measurements:

V1 - 444 volts on the plates, drawing 4 mA, which is about 1.7W
pin 3 - 526v
pin 4 - 527v
pin 5 - 15.4v
pin 8 - 77.9v
pin 7 - continuity to ground

V2 - 444 volts on the plates, drawing 4 mA, which is about 1.7W
pin 3 - 526v
pin 4 - 527v
pin 5 - 15.4v
pin 8 - 77.9v
pin 7 - continuity to ground

[Enzo]

Look lower right in the schematic, the notes. Your numbers look fine to me. This amp will naturally idle at low current. Pin 7 grounded is per the schematic.

How can you have "444v on the plates" and then "526v on pin 3" Pin 3 is the plate.

If moving a tube makes noise, either the pin has a loose grip or the solder is cracked. Or something similar.

[Tone Meister]

Look lower right in the schematic, the notes. Your numbers look fine to me. This amp will naturally idle at low current. Pin 7 grounded is per the schematic.

How can you have "444v on the plates" and then "526v on pin 3" Pin 3 is the plate.

If moving a tube makes noise, either the pin has a loose grip or the solder is cracked. Or something similar.

I think my CompuBias meter has taken a dump. The pin readings were taken at the tube socket, but the 444v reading came from my normally reliable CompuBias. Yes, it has a fresh battery.

I'll service those power tube sockets and see what gives. The amp seems to work just fine with the fresh power tubes.

[Tone Meister]

One more question: Should the two speakers be wired in parallel for 4 ohms or series for 16 ohms?

One speaker was wired reverse polarity when the amp got here in what looks like an attempt at series wiring; however, the way the speaker leads fit, it appears like it should be parallel for 4 ohms.

[Enzo]

Look at the schematic, it pretty clearly says 4 ohms by the main output jack.

[Tone Meister]

My bias meter was lying to me. I tightened the pins on both tube sockets and now have the speakers wired correctly in parallel for a 4-ohm load. Amp sounds healthy and all voltages are spot on, so all is well.

Thanks Enzo.