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Post by steveeb on Sept 21, 2015 21:02:10 GMT
I have recently acquired an integrated amp with a valve preamp stage. I'm getting a noise like - well, like a noisy valve hissing. I keep thinking it's started to rain again. Oh, it has! I've had some valves behave like this on startup, then settle down when warm but this is persistent, although intermittent. It will complain for about 30 seconds before abruptly stopping like it's been switched off. Silent for maybe 5 minutes then starts again.
I've systematically replaced each valve, including the rectifier valve, so I'm thinking I've ruled out the obvious. That's the end of my understanding.
Any suggestions for tests I can make for a process of elimination would be appreciated.
Oh, and it surprised me that I could still hear this 'distortion' through the drivers with the amp on mute.
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Deleted
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Post by Deleted on Sept 22, 2015 6:33:55 GMT
First, clean contacts on valve bases , has the amp got a Selenium rectifier ?
Then check old electrolytic caps, on Grid, and Cathodes,
A circuit would be good.
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Post by MartinT on Sept 22, 2015 9:17:35 GMT
Look at it in the dark. Is one valve glowing blue more brightly than the others? Could be a shorted bypass cap.
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Post by Deleted on Sept 22, 2015 10:38:53 GMT
Martin, yes that does happen, but it is a nice colour.
Check dates on caps also, and see that none have contain PCB if they do, remove and dispose correctly , nasty stuff. And not by fire please.
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Post by steveeb on Oct 29, 2015 12:43:25 GMT
Oh, how we laughed!
As investigation looked likely that it was going to require some technical acumen from someone less like myself, being totally unhampered by electronics experience or understanding, I gave the job to a valve amp repair company. After a week of running they reported that they couldn't hear any issue, a dead quiet amp.
Surprised, I could only accept that it was related to my own electrical or system interaction. Playing the amp and speakers at my neighbour's house also showed no issue. I methodically eliminated every component, speaker and cable interaction in my system, including a mains regenerator and tried only the amp and speakers through various power outlets, with the one that runs the system appearing worse. I replaced the wall socket with a new, unswitched one. Nope.
I turned off the water heating, central heating, fridges and freezers one by one, cooker, washing machine and any lights all off, without any change.
Then I noticed an SMPS serving a small tropical fish tank... Turned the socket off - Voila! Following a celebratory jig of relief and much damning of this particularly shite implementation of the technology I removed the offending device and sat down for my first real listen to what the amp could do. Excited or what! Surely my system would sound the bestest ever! Well of course the problem remained. Bollocks.
But rationality eventually replaced frustration; turning the socket off had worked. The second plug, that I assumed was only for the light (this tank is not my domain), also served a combined water heater and thermostat - which turned out to be the source of interference every time it kicked in!
I don't understand why this should only be affecting this particular amp and right now I don't care, the fish has mysteriously disappeared and my wife loves the sound of the new amp more than the idea of keeping fish. Happy Days!
Among several lessons learnt, one must be 'Don't Assume Anything'. Ask questions to isolate and confirm the problem before trying to apply expected solutions.
I used to have a strap-line "If you think you know already, you're not really searching". Lesson two, heed your own advice.
I couldn't find an emoticon with a big enough smile to express by feelings at the moment!
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Post by John on Oct 29, 2015 13:47:21 GMT
Great news Steve It can take awhile to get to the bottom of these type of issues but glad it now sorted
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Post by MartinT on Oct 30, 2015 13:00:36 GMT
I hate those hard-to-find problems that just nag at you. Well done for finding it!
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Post by jandl100 on Oct 30, 2015 13:28:59 GMT
Oh, how we laughed! ..... A fine tale, well told.  |
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