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Old 3rd April 2016, 12:33 PM
bikerhifinut bikerhifinut is offline
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Join Date: Jan 2006
Location: Penrith, Cumbria
Posts: 828
Default Re: KT88 Intermittent problem

Short of reflowing all the solder joints on the affected channel, If its a dodgy joint the only other way is to poke every joint with your chopstick....................
The "Cure" you suggest does point to the volume pot, don't think that just because its an expensive Alps pot and that its not crackly when rotated that it cant have an intermittent contact.
I say this because in the scrapbox I have a motorised Alps pot that was doing my head in as i was losing the signal at a certain point at the travel of the wiper. But not every time.
I'd be tempted to swop it out for a cheapie 50-100k pot and see if the fault reoccurs. We aren't worrying about ultimate sound quality at this stage of the diagnosis.
Another thing and I am not sure if it's been covered, have you discounted the possibility of a dodgy ECC83, or (less likely) 5687? I have also had issues with ECC83's especially old mullards going "Crackly" but not every time they were switched on. They usually display the fault by making a "rustling" sound when powered up. Whanging the level up might be causing a microscopic movement in the electrode structure that temporarily clears some sort of intermittent problem? Checking if its a 5687 is easier, just swap em over and see if the fault follows the channel.
These faults can be so frustrating, it took me ages to diagnose a dry joint on my WD88 on a coupling capacitor, it was only when I metered the voltage on the capacitor lead out wire that I discovered it as I'd been probing on the tags.
what sort of coupling capacitors are you using by the way? I have to say that I swear by the original Grey rectangular polyesters or the polypropylene soniqs jobs as being totally reliable.

Andy.
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