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Issues with my new RM20B

 
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DGL5150
RM20


Joined: 01 Apr 2013
Posts: 2

PostPosted: Thu Jul 27, 2017 6:31 am    Post subject: Issues with my new RM20B Reply with quote

Hi there,

I purchased a N.O.S Randall RM20B combo at the end of June this year. Sadly the shop was closing down so they were selling off remaining stock. I have used the amp for 2 gigs and some recording since purchasing with no issues.

Today I was recording with the amp in silent mode direct to my audio interface via the XLR output as I have done a few times before. After about 5 minutes the signal dropped significantly followed by some popping noises and then no sound at all. I immediately powered the amp down. After 10 minutes I changed the modules to rule out that as the issue. Still no sound and a humming sound from the speaker when in live mode, again I immediately powered down. I think there was a slight smell of 'electrical burning' similar to a motor being used which is leading me to believe the output transformer is at fault although I'm not certain.

I don't understand how this could happen as the manual clearly states that you can run the amp in silent mode in this way and I have had no problems doing this before. Can anyone suggest a reason why this would happen? Or what might be at fault?

Cheers
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tschrama
RM100


Joined: 04 Jun 2014
Posts: 187
Location: Netherlands

PostPosted: Thu Jul 27, 2017 6:54 am    Post subject: Reply with quote

so many things might have happened. Especially since it's a NOS item, electrolytic caps might have dried out.. if you want it to repair yourself, open it up and post some pictures, then we might help.
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warmachine67
RM20


Joined: 20 Apr 2017
Posts: 24
Location: Alabama

PostPosted: Thu Jul 27, 2017 4:28 pm    Post subject: Reply with quote

Something gave up the ghost and it could be the output transformer as the humming and no sound can indicate that.

You may have read on here that the rm20 and 22's transformers all around are susceptible to failure. They are just not high quality.

I sold an rm20 combo on eBay that I had been playing at bedroom levels for about two years without any problems only to have it fail right away when the buyer played on it for 30 minutes. So, it may not be something you did, it just happened.

Rob at jaded faith may be able to help you diagnose the problem if you want to contact him via his website and he is occasionally on here. His work is excellent and his prices fair considering how much of a niche market the mts stuff is.
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galao
Donating Member


Joined: 05 Dec 2008
Posts: 88
Location: Berlin, Germany

PostPosted: Fri Jul 28, 2017 11:40 am    Post subject: Reply with quote

Donīt know about your technical knowledge and if you are able to test the OT yourself.

If the OT is really fried, you may consider buying a generic VOX AC15 tranny like the one from Classic Tone. The RM20 and RM22 power amp design is pretty close to the AC15.
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