"Serge Auckland" wrote in message
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"Iain Churches" wrote in message
i...


"Fleetie" wrote in message
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Hi.

While I'm here, does anyone know the usual cause for a valve amp
constantly "rustling" out of one channel? Mine is doing it
intermittently and sometimes loudly, out of the left channel.
Is it likely to be a resistor burning up, or something about
the valves? Is it likely to be in the output stage valves or
cathode resistors, or...? It's starting to drive me nuts!

Is this the kind of symptom that tends to always have the same
cause?


Hello Martin.

The first thing I would suspect is the contact between the
socket pin grips and the valve pins on the input and driver
tubes, particularly if they are B9A type (miniature nine-pin)
Some (particuarly Chinese) valve bases have contacts that
open up, and don't contract again to grip the pin firmly.

If this is the cause, you can find the culprit by a little
"waggling" (these hi-tech solutions are often the best!)

Then, switch the amp off, pull out the valve, and clean the pins
with aerosol contact cleaner. Spray a little into the valve
base also.

As well as the above, have a look at the valves themselves when on. I had
a valve once that did what you've reported, and it was caused by the
vacuum having gone "bad". It was visible as a much greater than usual blue
glow. All valves will glow blue slightly, especially the larger power
valves and rectifiers, but if one is glowing more than the others, that
might be the culprit.

Yes. Often when swopping valves from left channel to
right channel to find the culprit, you may find the problem
disappears, as the action of fitting and removing cleans the
pins a little. I recently had a preamp on my bench with an
ECC82 which was silent in the left channel, but rustled when
on the right.

Iain