[Jukebox-list] Diagnosing AMI amp without a tube tester

[Jay Hennigan]

David Breneman wrote:

> At my 4th of July party, the machine started sounding distorted
> after several hours of play (remember, this machine stays powered
> up 24x7, like the audio was clipping.  The right-hand output tube
> had a real hot spot on its plate, glowing orange on one side. If
> I let the machine sit (still powered up) for a while it played OK
> for two or three records, then the glow and distortion started again.
> It is safe to assume that the culprit is this tube?  Or does this
> sound to anyone like a sign of rebuild time?  Thanks!

The coupling capacitors have probably gone leaky, causing the output 
tubes to saturate.  This will damage the tubes and eventually the 
transformers.

Definitely rebuild the amplifier if it hasn't been done recently.  Even 
if it has, it would be worth checking out as there is likely a problem 
with the tube bias.

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
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