Vox AC30C2

[Jazz P Bass]

Go back & recheck the voltages on the PI tube.
Pin 1 & 6: plate
Pin 2 & 7: grid
Pin 3 & 8: cathode (power off, make sure these two are tied together.

You need to see 200 some volts, dc, on the plates.
44 some volts on the grids
60 some volts on the cathodes.

If the voltages are way off, try the test again with the power tubes removed.

[pnut5150]

Here are my results:
Per tubes in
Pin 1: 210.6v
Pin 2: 10-11v(spikes up and down)
Pin 3: 13-14v(spikes also + tied w/8)
Pin 6: 210.6
Pin 7: 10-11v(spikes)
Pin 8: 13-14v(spikes)
Power tubes out everything the same except for now I have 261v on 1 & 6

[pnut5150]

I also see they are 2 capacitors there: C45&C48.. I do not have a cap tester..do they Look like they could be knocking voltages down to screens and grids? And C50 also, r112 voltages are in the mv range.

[Jazz P Bass]

Have we measured pin 8 to ground?

Power off.

I would hope that you are measuring AT the tube sockets, as there is a jumper cable in between.

[pnut5150]

I am measuring solder side of tube sockets.
Pin 8 to ground is 48.1k ohms. That is what u are looking for ohms reading from pin8 to ground? Correct?
I did last night check the jumper cable with a resistance reading, it all seemed fine.

[g1]

A few thoughts. You said in PM that if you plug guitar to input and connect send to another amp it sounds fine. This indicates preamp and power supply are ok, problem is in power amp section.
Phase splitter voltages are not right and pulsing.
What may be happening is a bad solder connection that is failing under current and cycling between making/breaking connection. A bad connection such as this would probably read ok on a meter when amp is turned off.
It appears there is some kind of ribbon cable or several jumpers which are shown as "J" connections for each of the tube elements.
Try resoldering them as well as the tube socket.

[pnut5150]

I did something stupid, I knew better to do, but I did it anyhow. Well when the old tubes were in, the heater fuse blew, well when I installed new power tubes I didn't have a good fuse for heater so I wrapped wire around the fuse(stupid stupid stupid). Well I put a good fuse in just now and it popped it as soon as I turned power on. As long as I leave V6 out, the fuse is fine and amp pops and cracks and voltage on PI tube is spiking up higher to where it should be. R101 beside power tube has negative voltage now and most of the power tube socket has negative voltage except the two 300v pins. Any ideas?

[pnut5150]

What is R101, R104, R61, & R81? They are all dead tonight. Ohms readings are correct. 3.3k ohms

[Jazz P Bass]

R101 & R61 ( & R81 -R108) are the output tube grid pins.
That is where the signal comes in, from the PI.

This is a cathode biased output, so there will not be a grid voltage unless the tubes are in, the screen resistors are good & the cathode resistor is good. (R119)

R 104 is a screen resistor.
It should have 300 some volts on it.

[pnut5150]

All the screens have 300+v on them, with tubes back in the grids have a 2-3v on them. Sometimes the volume is trying to kick in, then it fades out. Something smells hot, and on pin6 of v6 I have some 30v while on the other power tubes, they only have mv on pin6. Could I have a faulty ceramic socket?

[Jazz P Bass]

Pin 6 is not connected internally on the EL84 tube.
Although the board layout may use it for something (that is more a Point to Point thing)

Pins that matter:
Pin 7: plate Vdc
Pin 9: screen Vdc
Pin 3: cathode Vdc
Pin 2: grid
Pin 4/5: heater

Pick one tube/ one socket & measure the above pins.
Same socket, try another tube.
If all tubes behave, move to the next socket & measure that, down the line.

[g1]

on pin6 of v6 I have some 30v while on the other power tubes, they only have mv on pin6. Could I have a faulty ceramic socket?

Yes you may have a bad socket.
Sounds like the V6 socket has a few issues? Putting a tube in it causes heater fuse to blow, and there is an odd reading on pin 6 that is not on the other power tube sockets?
Is there any visible burning on the socket?

[Enzo]

Um, this is an AC30, aren't those EL84, not EL34?

And pin 6 on an EL84 is or at least can be an internal connection. If there is a funnny voltage on pin 6 of the socket with the tube removed, you may be onto something, but if it follows the tube it may be normal.

The pc board trace art seems to have no connections to pins 1,6,8.

[pnut5150]

V6 is the only tube that has the odd reading on pin 6, I checked pin 6 on the other power tubes and they are in the MV range. I'll chart voltages so you guys can see them. Thanks again for your time and replies.

[Jazz P Bass]

V6 is the only tube that has the odd reading on pin 6, I checked pin 6 on the other power tubes and they are in the MV range.

V6 the only 'tube' or V6 the only 'socket'?

If you narrowed it down to a single tube , great.
If you narrowed it down to a single socket, also great.

Which one is it?