lack of treble

[mosschops]

Hi all new here got a slight problem with my kat 6500 amp its has been out of use for a number of years. the problem is a lack of treble on one channel I have tried all new valve and cables
Regards Steve.

[bob orbell]

Hi Steve, I take you mean a KAT6550, are you sure that the speaker tweeter is working on the channel that sounds poor, you can try reversing the speaker cables on the KAT, or try another amplifier if possible. Bob

[Richard]

Hi Steve and welcome,

Did you swap speakers (or the connections at the amp) L to R to check for a faulty tweeter or xover component? Ditto source.

If the fault stays with the same channel I'd suspect electrolytic capacitors next. They may be 20 years old now and will go off if not used for years. A failing cathode bypass cap(s) may allow degenerative feedback which woul lower volume and lessen bandwidth and may be the effect you hear. Even if they aren't at fault it would be a job worth doing if putting the amp back into use,

Start with ECF80 caps C9/10 then 6550 caps C15,16,17,18.

Also check the coupling caps C11,12,13,14. If they are plastic film (original were orange ployester) they should be fine but if they were changed to paper in oil type they can go leaky.

If keeping it I would go on to swap out the PSU caps C1,2,3,4,5,6, but humming/noise on both channels would be more the fault here rather than the problem you describe.

[Richard]

Ah, morning Bob

[bob orbell]

Good morning Richard. Bob

[mosschops]

Many Thanks Richard it is the right channel the problem moves from left to right when i swap speaker cable on amp .I have some new caps that i will try i will let you know how it goes
Regards Steve

[mosschops]

Hi Richard put in new signal capacitors yesterday all now seems well. They were copper foil paper in oil {ampohm make} about 15 years old. The new ones are clarity capacitors from hifi collective.
Many Thanks for your help
Regards Steve.

[Richard]

Excellent, good to hear Steve