Replace OT on a Laney GH50L?

[Thee Abomination]

An amp tech told me the reason my Laney is so hummy is because of the output transformer. Not that it's malfunctioning, it's the design. It's one of those sort of donut shaped ones wrapped in clearish plastic. I was wondering if a new transformer might help and possibly improve the sound overall. If so, can you recommend one?

Thank you,

TA

[Gingertube]

Hi TA,
Feeling feisty today so ---- Get a new amp tech - this one is not too good.

The usual reasons for bad hum is badly out of balance push pull output stage. When the idle currents are matched then hum cancels in the output transformer.

Toroidal Output transformers are reputed to be less tolerant of idle current imbalance and that is probably what your tech was talking about but that relates to hifi toroidal output trannies. Thiose for guitar will be adequately air gapped to cope with any idle current imbalance.

I would get a new matched pair of output tubes and see if the hum goes away, actually I would mod the amp to have individual idle current adjustment for each output tube and than set the idle currents to match.

This sound like one of those stories amp techs tell when they don't want to be bothered with the extra work to make it right or to excuse the indiferent results when they have run out of knowledge of things to try.

Cheers,
Ian

[Thee Abomination]

Hi TA,
Feeling feisty today so ---- Get a new amp tech - this one is not too good.

The usual reasons for bad hum is badly out of balance push pull output stage. When the idle currents are matched then hum cancels in the output transformer.

Toroidal Output transformers are reputed to be less tolerant of idle current imbalance and that is probably what your tech was talking about but that relates to hifi toroidal output trannies. Thiose for guitar will be adequately gapped to cope with anuy idle current imbalance.

I would get a new matched pir of output tubes and see if the hum goes away, actually I would mod the amp to have idividual idle current adjustment for each output tube and than set the idle currents to match.

This sound like one of those stories amp techs tell when they don't want to be bothered with the extra work to make it right or to excuse the indiferent results when they have run out of knowledge of things to try.

Cheers,
Ian

Thanks for the quick reply, I had the output tubes changed but I don't know if they were matched. Preamp tubes were replaced as well as some other things which I can't remember. I need to find somebody in the Dallas Fort Worth area who knows what he's doing I guess.

[Gingertube]

The service manual with schematics is here:
LANEY GH50L SCH Service Manual free download, schematics, eeprom, repair info for electronics

The schematic (which also covers the GH100L) shows a fuse in the heater centre tap connection to ground, identified as T5A - If you have a lot of hum I would be checking that that fuse is intact.

Cheers,
Ian

[Thee Abomination]

Will do.

Thank you.