KIT 6550 - hum

[bob orbell]

The parts are on their way to you Waverley, you also have a PM. BOB

[waverley]

I'm delighted to be able to report that thanks to Bob's help in obtaining the parts, my 6550 is now up and running again.

The fault was in the smoothing caps. One was visibly faulty, and the others presumably were not long for this world. It does get quite hot in there!

Thanks again to Bob, and thanks to other members for your helpful comments and interest.

[bob orbell]

Thank you for your kind words Waverley, glad all is sorted. BOB

[Infinitely Baffled]

Hello, All. I was interested to read this post, since I too have a hum problem with my Kat 6550. The difference in my case is that it was newly-built a couple of months ago, so I am discounting the possibility of capacitor or other components having reached the end of their lives.

I received help and suggestions from you fellows on the forum during the build, and I reported back at the end that it was all satisfactory. And so it is - broadly speaking. I am very pleased with the sound of the amp but after a couple of months' use I am getting increasingly niggled at the level of hum it produces. This was always there from first the switch-on, but I was happy enough to overlook it at first in the euphoria of completing a functioning build!

There are two sources of this hum: first through the loudspeakers, and secondly from the amp itself. I am not too worried about the sound coming through the speakers - it is a bit more than other amps I have, but it is livable-with. I am more bothered about the sound which emanates from the amplifier itself and which is quite noticeable when you stand near it.

My question is: how hummy is the Kat 6550 anyway in your collective experience, and might it be normal? Otherwise, what might be wrong?
Cheers and regards
Infinitely Baffled.

[Richard]

Mechanical hum will be from the mains TX or the choke. It will be using the chassis and shelf as a sounding board. Try tightening and loosening the bolts of these to the chassis. Try using rubber grommets to mount them (but fit a wire to make sure the metal is earthed to the chassis). Try fitting soft rubber feet to the amp. Check the base plate isn't causing it. Pressing and prodding to see if you can vary the sound might give some clues to a fix

[Infinitely Baffled]

Brilliant! Many thanks, Richard. I'll get prodding. Cheers. Gary.