Another noob question. When I disconnect the speaker and connect a dummy load...

[Jimmybjj]

BK 3001 signal generator into amp (aa764) into dummy load. When the speaker is completely disconnected, i can hear the signal from the generator coming from the amp, tone changes as i turn the knob on the generator. I called my wife in to see if i was just hearing things and she confirmed this. Why can I hear the signal? Where is that sound coming from?

[Enzo]

It is your output transformer "singing" most likely.

Roll up a magazine into a cylinder, or use the cardboard tube from a paper towel roll. Hold it to your ear and use it to listen around the amp. Like a stethoscope. That should make it easier to pinpoint sound sources.

[Wilder Amplification]

Yep...you're hearing output transformer ring. Perfectly normal.

[guitician]

The transformer coils are moving the air

And it is most noticeable around 1 khz where your ears are most sensitive. I've heard that on every tube amp I've ever hooked to a resistive load.

[Jimmybjj]

good, I'm glad to "hear" this is normal. if anyone can explain , why can I hear the signal? as I understand (which isn't much, yet) the output transformer is just cores and coils, I don't see the potential for this signal to be heard audibly. I guess it's not really important that I undertand this with everyhig I need to learn about tube amps itself, just curious.

[Wilder Amplification]

Believe it or not, as tightly wound as the coil wire is, the magnetism of said wire is enough to cause the coil wire to move just enough to produce the sound you're hearing.

[guitician]

The wires are moved by the electromagnetic fields inside the transformer and this motion is transferred to the insulation wrapping and then to the air where it is picked up by your ear.