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#1 (permalink) |
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Member
Join Date: Mar 2009
Location: Norway
Posts: 51
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JTM45 RI noise/hum when power up
Hi
Just got a '89 JTM45 RI. It makes loud hum/noise when I turn it on, much more than my other tube amps. What could be wrong? Or is it suppose to be like this? Most of the hum goes away when I turn off standby.
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Cheers! Øystein |
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#2 (permalink) |
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Junior Member
Join Date: Jan 2010
Posts: 4
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Re: JTM45 RI noise/hum when power up
Mine has the same problem, also an 89 model. I joined here to see if I could find an answer.
Mine had it when it was completely orignal and still has it after I replaced everything except the power transformer. I installed PTP board, Marstran OT, new pots, choke and filtering. The problem must have something to do with the power transformer or wiring from it - I've emailed Marshall to see what the current PT they are using is in the reissues. I'll let you know what I find out, but something must have changed because the new ones don't hum in standby. |
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#3 (permalink) | |||
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Senior Member
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Re: JTM45 RI noise/hum when power up
Quote:
How bad/noticeable is the hum?
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Jon Wilder Wilder Amplification sales@wilderamplification.com tech@wilderamplification.com Quote:
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#5 (permalink) |
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Senior Member
Join Date: Nov 2008
Posts: 2,719
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Re: JTM45 RI noise/hum when power up
That can be normal. When the PT is not under load, it emits more EMF and that is coupled into the OT.
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Marshalls: 1983 JCM 800 2204, 1987 2550 Silver Jubilee, 1993 JMP-1, 1997 JCM2000 DSL50 Marshall Cabs: JCM800 1960a G12-65s, JCM800 1960a G12T-75/Century, JCM900 1960a G12M-25/G12H-30 70th, JCM900 1960a Cab with Marshall G12-Vintage speakers Other: 2008 2550x Marshall Silver Jubilee SDM Layout, 2009 Union Jack JTM45, 2008 Vox AC30CC 2x12 combo, ADA MP-1, 2x12 2550x Cab with Vintage 30s |
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#6 (permalink) |
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Member
Join Date: Mar 2009
Location: Norway
Posts: 51
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Re: JTM45 RI noise/hum when power up
Yeah, hum/noise goes away when I turn off standby (play mode), and works great.
Well, not great, have some problems with the sound fade away when I run both channels and a boost in front. I made another topic for that. Havn't had time to re-check bias yet.
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Cheers! Øystein |
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