My Laney Pro Tube AOR Series amp is making a very disturbing, rising squeal as the tubes heat up, and I can't find any reference to this happening to anyone else anywhere. I'm inexperienced with tube amp technology other than online research, but I'd like to avoid taking this in to be fixed if possible.
The squealing noise begins soon after the tubes begin to glow, and rises in volume and pitch
The noise is affected by the master volume
I replaced the can (50uf, 50uf, 500v) after being told it may be a failing filter capacitor but the problem remains.
A quick lookover shows white chalky residue on the electrolytics, and one capacitor bulging on the + side
Oxidation between the power tube glass and base
The tubes all look like this
Will I need to do a full electrolytics replace or is it something entirely unrelated?
The squealing noise begins soon after the tubes begin to glow, and rises in volume and pitch
The noise is affected by the master volume
I replaced the can (50uf, 50uf, 500v) after being told it may be a failing filter capacitor but the problem remains.
A quick lookover shows white chalky residue on the electrolytics, and one capacitor bulging on the + side
An externally hosted image should be here but it was not working when we last tested it.
Oxidation between the power tube glass and base
An externally hosted image should be here but it was not working when we last tested it.
The tubes all look like this
An externally hosted image should be here but it was not working when we last tested it.
Will I need to do a full electrolytics replace or is it something entirely unrelated?
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After tapping each with a pencil, none of them appear to be microphonic
I may just not be able to hear any microphonic noise over the loud screeching that the unit is already making
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The glue between glass tube and plastic base is irrelevant.
The blue filter cap with the bulging vent and white goo need to be replaced.
The first couple filter caps are there to smooth power supply ripple and stop hum. But later ones are more for decoupling between preamp stages. If one of those caps, like the one in your photo, go weak, you could have unwanted coupling between stages, resulting in oscillation.
Replace those spoogy caps. It may help, but it needs to be done regardless.
The blue filter cap with the bulging vent and white goo need to be replaced.
The first couple filter caps are there to smooth power supply ripple and stop hum. But later ones are more for decoupling between preamp stages. If one of those caps, like the one in your photo, go weak, you could have unwanted coupling between stages, resulting in oscillation.
Replace those spoogy caps. It may help, but it needs to be done regardless.
The output transformer is still original, I think all but the tubes are. It is an AOR Pro Tube 30.
Will follow the circuit back looking for faulty wiring, microphonic caps etc. Should I use a voltmeter also to find where the oscillation is coming from?
Cheers for the advice, I think the electrolytics are due a change anyways, they're unchanged since 1987
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