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Jim5150 15th June 2009 02:52 PM

Scratchy clicky noise coming from homemade 6L6 tube amp
Hi all ,

Got a bit of a problem and need some help, recently I built myself a 100W Power amp for use with my line 6 pedalboard. The amp has a 12Ax7 first stage to just increase the gain to line levels, a 12AT7 phase splitter and 4 6L6GC tubes and is based on a standard boogie type/ fender power amp design there are no tone controls just a volume which is controlled/coupled to the phase splitter. The problem I've got is that I get a scratchy type sound coming from it, the type of sound you get when you turn a dodgy pot or fiddle with dodgy lead or input but it's constant.
The sound is always there at the same volume no matter if the volume is down or way up. I've tried changing the the 12Ax7 and the AT7 but to no effect. Is there a resistor or a cap breaking down somewhere maybe a dodgy solder joint? If so does anybody have any ideas how to pinpoint it. Is there anything I should be focusing my intentions on. The bias supply for instance? I'm thinking that the Power section is at fault due to the fact that when the volume is at 0 the scratchy sound is still there and as the volume is controlled at the phase splitter section this rules out anything before. Anybody have any ideas.
Any help would be much appreciated?



Poindexter 15th June 2009 05:09 PM

Clean the tube pins and sockets.


m6tt 15th June 2009 07:40 PM

Check bias, limit bandwidth (i.e. use grid stoppers), and clean as mentioned. Sometimes it's RF coupling from various stuff like motors, other times it's cathode noise from too high current, or of course spurious resistances from dirty sockets.

kevinkr 16th June 2009 04:45 AM

How about a schematic and a few pictures of your project as these might provide some clues in order to take a shot in the dark at what ails this thing. :)

Jim5150 25th June 2009 10:53 AM

Hi Guys , I cleaned the tube sockets with some alcohol type cleaner and although the sound hasn't completely dissapeared it's better and doesn't bother me anymore . So thanks for that.

Will post some photo's and some hand drawn schematics when I get a chance. As although the amp is working the sound is not quite what I want , so I may start a new thread reviewing my design and what I can do to improve the sound quality etc...

But thanks all for your help

Much appreciated


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