Bare Knuckle Pickups Forum
Forum Ringside => Tech => Topic started by: maliciousteve on December 25, 2006, 05:59:32 PM
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Hey guys. Recently my amp has been playing up now and again. Sometimes when I'm playing, this scratchy sound builds up, lasts a few seconds and then disappears. It's not my guitars or leads because the leads are new and the jack sockets are clean. What does this sound like?
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Electricity arcing on a valve socket?
I wish I knew...
I sometimes get it on my Marshall
Sounds like a rustling noise
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Yeah sounds exactly like that. I've looked at the valves when that happens but I don't see any electricity arcing. It's really confused the hell out of me.
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I had this on my Mesa too. At first thought a valve was on its way out - but that usually sounds like distant gunfire, this noise was like tissue paper being ripped. Then I thought interference from a satellite dish - it started when I moved my music room & the dish was on the outside wall right next to the amp, but I ruled that out.
It seemed to come on within a few minutes of me starting to play. I eventually worked out that it couldn't be a lead - it still happened with nothing plugged into the input or FX loop & a new speaker cable.
One day I left the amp on all day, by early evening it stopped & I haven't noticed it come back since.
Damned if I know what it was either... :?
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I've been thinking about it and it may be something to do with the warmth or the valves. Usually I wait till I hear a 'click' in the amp, which usually indicates that the valves are ready. So i've left the amp on standby for a bit longer and it doesn't seem to happen now. So my guess at the moment is that the valves may not have been ready enough and the surge of current may have caused the 'wishy washy' sound to have happened.
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When I used to repair Televisions and amps with valve powered sound stages, a thin film of oxidisation would sometimes build up on the pins of the valves.
The cure was usually to remove the valve, clean the pins with very fine emery cloth, use a fine needle file to clean the pin sockets, close the pin sockets up a bit tighter with the point of a needle file or tiny screwdriver, then spray valve pins and socket with a quick burst of WD40 or "Servisol".
If you do not have the tools, just spray the (cold !) valve pins and sockets with a moderate amount of WD40 or Servisol and shuffle the valve around in it's base. This usually cures the intermittent contact causing the problem.
Out of interest, I had a similar problem with one of the 12AX7s in my Peavey Classic 20 and a quick spray of WD40 on the pins and a 'shuffle' in the socket cured it.
This problem I have more often found in the pre-amp stages, as the fatter pins of the 6L6 or EL34 type output valves were less prone to this problem. With an EL84 output stage, you still have the 'small pin problem' . In a Television or record player/radio it was usually a single ECL82.
The point Malicious Steve raised about warming the amp up first was very valid in that a hot valve pin usually expands enough to eventually tighten the contact between pin and holder.
While you are doing that, it is always handy to spray the volume and tone controls as well if you can get easy access.
Hope that helps.
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All good points by Fourth Feline but I wouldn't recommend WD40 on pots - you're gonna freeze them up. better to use a 'lubricated' spray such as Servisol pot cleaner.
The Servisol 'non lubricated' spray is good for valve bases and switches - you don't really want any residue on your valve pins.
:twisted: