I'm really new to tubes and need help in debugging a Quad II.
When I power on the amp the rectifier tube internally arcs and
obviously overheats in a matter of a few seconds ( power pulled
quickly !). The fuse doesn't blow .

Things I've done:

Without any tubes in, checked power tranny. Volts OK.
Caps replaced, resistors checked. Checked power to rectifier socket
OK.

Inserted a couple of cheap 6L6's but without rectifier tube, powered
up, tubes behave fine.

Tried another recifier tube thinking the first had issues, same
problem.

Sounds like the power transformer side of the circuit is OK. Would a
fault in the output transformer or choke cause this?

Any help appreciated.

( I could take it to a tube tech, but how would I learn anything ? )

Jeff