Power supply rails seem ok with power amp section isolated. When
connected the waveforms indicate a heavy load. The amp briefly worked
after a lot of hissing and then (after I connected an input signal)
returned to its usual state of hum so I'm off to recheck solder joints
& earthing.

Thanks

Duncan

Arfa Daily wrote:
"Madarchol" wrote in message
ups.com...
Anyone help me with this? Its an old 4*12 combo which worked fine until
recently when it developed an intermittent click approx every 5
seconds. occasionally upon turning the power on it would just produce a
50Hz hum through the speakers.

Now that is all that it does! Grounds all seem to be fine. pre amp
filter caps, and all power supply components are OK also. There really
isnt that much inside this amp so I can replace it all (apart from the
output transistors which seem to be obsolete), but if anyone has some
time saving ideas I'd be grateful.

Thanks

Have you actually 'scoped the power supply rails to check for ripple, and
checked the voltages in case a leaky cap or leaky zener in the preamp supply
( a common problem on many makes of group amps ) is dragging down any of
them ?

Arfa