Nostromo Posted March 15, 2011 Share Posted March 15, 2011 (edited) Hi, After many years of totally trouble free use and fantastic reliability, my SWR SM-500 has developed a very loud buzz when first switched on from cold. When first switched on it now buzzes away very loudly for about 3 to 4 minutes whereafter the buzz fades away from loud to nothing over about two minutes and after that it performs fine ? . . . it acts the same whichever bass guitar / guitar lead / cab / cab lead I use with it. It only started doing this about three weeks ago and never ever did it before - I'm wondering if I'm hearing a pre-curser to bigger problems or a breakdown ahead ? It’s not my main gigging amp, but I use it every week for practice and always take it to gigs as a standby/understudy for my valve gigging amps. Big question is - if the loud buzz is trying to tell me something is wrong, then would it be worth having it serviced now or is it best to wait till it actually breakes down (if indeed it even is going to break down ?) before I take it to be looked at ? Or can anyone else assure me that such buzzing is ok and normal for a cold SWR SM-500 ? . . . . . Edited March 15, 2011 by Nostromo Quote Link to comment Share on other sites More sharing options...
icastle Posted March 15, 2011 Share Posted March 15, 2011 It's not normal. IIRC this amp has a single valve pre-amp, it could be that the valve is faulty and crawls back to life once it's heated up sufficiently. Quote Link to comment Share on other sites More sharing options...
Nostromo Posted March 15, 2011 Author Share Posted March 15, 2011 [quote name='icastle' post='1163588' date='Mar 15 2011, 08:00 PM']IIRC this amp has a single valve pre-amp[/quote] Yes you do recall correctly, its got 12AX7 pre amp valve I think, and, my SWR SM-500 has, I would estimate, run for between 1000 and 1500 hours altogether since new on this same valve. Its never been changed. I dont know what the normal service life of a 12AX7 pre amp valve ought to be ? Maybe the valve is wore out ? Quote Link to comment Share on other sites More sharing options...
BIG.J Posted March 15, 2011 Share Posted March 15, 2011 Had the same in the past, Valve sometimes isn't quite sitting snugg... J. Quote Link to comment Share on other sites More sharing options...
icastle Posted March 16, 2011 Share Posted March 16, 2011 [quote name='Nostromo' post='1163601' date='Mar 15 2011, 08:10 PM']I dont know what the normal service life of a 12AX7 pre amp valve ought to be ? Maybe the valve is wore out ?[/quote] There are too many variables to put an 'expected life' figure on it unfortunately. As Big J has also pointed out, it might be that the valve isn't firmly seated in the socket. From what you've described I'd certainly be looking somewhere around the valve area. Quote Link to comment Share on other sites More sharing options...
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