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Author Topic: JTM45 HUM  (Read 5318 times)
iwantogo
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« on: June 06, 2008, 03:23:35 PM »
I have a 2 month old JTM45 built by Nik and sent to me. It has master vol. in rear of amp. The past 3 or 4 times I've turned on the amp, I've noticed a HUM that is constant with the amp on and the stand-by off. It happens with or without the guitar plugged in. This didn't happen when I first got the amp but developed over time. This is not a grounding problem.

Any syggestions to look for to fix this problem. The hum is loud enough to hear during live performances when the band stops playing or during a quiet music time and would be totally unacceptable for recording.
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Lefty
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« Reply #1 on: June 07, 2008, 10:21:34 AM »
Try swapping pre amp tubes. Could be as simple as V1 gone bad?
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iwantogo
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« Reply #2 on: June 09, 2008, 02:20:02 PM »
I did change the V1 tube and the Hum did infact go away. When I got the amp a few months ago, I noticed how sensative that tube was in unwanted sound. Both by touching the tube and the chassis around the tube. Anyway, I replaced it with another JJ and the hum went away. I'll see what happens.
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iwantogo
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« Reply #3 on: November 17, 2008, 08:34:19 PM »
Just a note about a change in the power tubes (KT66's) as well. A few weeks ago I started to notice that certain bass notes on the guitar were coming out with an octive lower ghost note. I was not getting a clear note but getting two notes and overtones. It was not sounding good.

Nik and others thought it was the power tubes doing that. I noticed that when I put the head on the floor and not on my cabinet, the problem seem to go away. I put the head back on the cabinet and it did it again. It seemed that the power tubes were vibrating and very microphonic. I just put in those tubes about 5 months ago and were KT66 tubes marked "Ruby" that I got from Mike at KCA. I replaced the tubes and the problem went away. I just thought that I would get a lot more life than 5 months from a set of new power tubes. I had them biased at 38. I've been wondering if anybody else has noticed short lived tubes in their JTM45 and if there were noticable improvements in which tubes they were using in both the power and preamp section of the amp??

I need to get another matched pair for a backup to take on gigs on the road.
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