VH-4S bias imbalance.

[Sixtonoize]

I've got a matched quad of =C= 6550s that I threw in my VH-4S, and I can't get the bias anywhere near matched.
Right now, one transformer has about 19ma per tube and the other is around 50ma per tube.

The individual tubes are matched pretty well in each transformer, but the two transformers' readings don't match at all.
If I swap the tubes, the bias stays relatively the same - it's still 19ma or so in channel A and 50 in channel B.

I can adjust the bias lower, but that lowers the bias to both trannies equally, so I end up getting readings like 9/9ma and 40/40ma.

Any help/suggestions?

 

[duesentrieb]

Do you measure with croco-wires or directly with the probes of the DMM?

 

[Peter Diezel]

Please check the white screen resistors on the
tube sockets and the tube fault fuses.

 

[Sixtonoize]

It looks like I had a blown tube fault fuse.
The screen resistors all look good and measure at +/- 1k.

So now I just need to replace the fuse and the power tubes, or is there anything else I need to take care of first?

 

[Peter Diezel]

Replace the fuse and check the power tubes if
the fail.

Make a mechanical test with slightly knocking
on the glas of the tubes.

Thanks,

Peter