QUAD II HELP

[zulu]

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

[Mike Diack]

On 12 Aug 2003 18:44:25 -0700, (zulu) wrote:

>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

Any of the following would cause this problem :
Internal short to ground in output transformer.
Ditto Choke.
Stuffed resevoir/filter cap.
With **no power applied**, put an ohmmeter between cathode of GZ32 and
chassis. Needle should kick then sink back to infinity.
Any residual resistance indicates one of the above problems.
The above test is not definitave as it may be breaking down at high
voltage.
M