Aria Pro AG30 tube amp...anyone familiar with

[Helmholtz]

I've never seen that either, but can't think of anything else that would explain the readings.

First of all I would have to know where and how the12.6V was measured.
Can't believe that was between the heater pins of a tube socket.

[TomCarlos]

Gents.... I am sorry if my prior entry was not clear. With the ground connection in (as designed) and tubes removed, I am measuring 6.8 volts across the heater pins on all tubes. With the ground connection and tubes installed, I am measuring 6.3 volts across the heater pins on all tubes. If I remove the ground connection and remove the tubes, I measure approx 12.8 volts across the heater pins on all tubes. I do not want to put 12.8 volts (or something close to it) across the heater pins.

[Helmholtz]

With the ground connection in (as designed) and tubes removed, I am measuring 6.8 volts across the heater pins on all tubes. With the ground connection and tubes installed, I am measuring 6.3 volts across the heater pins on all tubes.

That shows the normal effect of loading the heater winding.

If I remove the ground connection and remove the tubes, I measure approx 12.8 volts across the heater pins on all tubes.

Now that's a kind of mystery.
I can only assume it's a measuring artefact and heater pin voltage would probably collapse to 6.3V with tubes in.
Why did you even try with disconnected ground wire?
Generally heater supply needs a ground reference.

[TomCarlos]

Why did you even try with disconnected ground wire?
Generally heater supply needs a ground reference.

When I received the amp, I was suspicious if any work had been done to the circuitry. I found the ground wire connected to the heater pin on V4, thinking it might have been something a prior owner did by mistake (since there was a glob of solder). So I did some checking before turning on and installing tubes. That is when I noticed the amp needed that connection.

[g1]

I do not want to put 12.8 volts (or something close to it) across the heater pins.

I don't think it is possible that there is 12.8V there when tubes are installed, no matter whether the ground jumper it there or not. I'll cover the cost of any damaged tubes if I'm wrong.
(also, what is written at the 2 green wires on transformer?)

[TomCarlos]

I don't think it is possible that there is 12.8V there when tubes are installed, no matter whether the ground jumper it there or not. I'll cover the cost of any damaged tubes if I'm wrong.
(also, what is written at the 2 green wires on transformer?)

Previously, I reported that with the tubes removed and no ground connection, that is when I saw 12.8 volts.

Ok, hearing that G1 would buy me a round of tubes, one last test. :-) And I bow to him for his foresight into what I would find.

This time, I left all tubes in the circuit, I disconnected the ground wire from V4, and in fact, I did measure 6.35 volts across the heater pins. ! And yes, the amp works in that mode. HOWEVER, there is a loud buzz coming out of the amp. So when I reconnected the ground wire to one of the heater pins on V4 (and of course that feeds to the other tubes), the buzz is gone.

Unfortunately, there are no markings on this transformer other that a couple Chinese markings most likely for the manufacturer.

So there you have it...

[Helmholtz]

This time, I left all tubes in the circuit, I disconnected the ground wire from V4, and in fact, I did measure 6.35 volts across the heater pins.

See post #34 .
Means that the doubled voltage was not "real".

And yes, the amp works in that mode. HOWEVER, there is a loud buzz coming out of the amp. So when I reconnected the ground wire to one of the heater pins on V4 (and of course that feeds to the other tubes), the buzz is gone.

That's normal when heater voltage has no ground reference.

[g1]

Thanks for indulging me Tom.
That is what I expected, voltage good, lots of buzz. As Helmholtz mentioned, there is not usually such a difference between loaded and unloaded voltages, but in this case it seems that is just the way it is.
Should you find the 60Hz buzz is still excessive, you could try any 1 of the usual heater-ground reference schemes:
-one side of winding grounded (as currently installed in this amp)
-humdinger pot (to ground or to some elevated DC voltage)
-resistive artificial CT (to ground or to some elevated DC voltage)

[Helmholtz]

Thanks for indulging me Tom.
That is what I expected, voltage good, lots of buzz. As Helmholtz mentioned, there is not usually such a difference between loaded and unloaded voltages, but in this case it seems that is just the way it is.

From post #33 the unloaded heater winding voltage is 6.8V.
The 12.8V seems to be a kind of "ghost" voltage.