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amp and unwanted speaker vibration

I like to seek opinion and advice from  Audiogon members.  When I connect my tube  amp (Lectron HJ50) to  my speakers ( Focus Audio Model  78) , unwanted vibration of speaker cone would occur.even  with all other equipment off.  The simultaneous vibrations from both speakers  would start to occur very rapidly and  consecutively   after I turn on  the amp for about 30 min.  However, when I plug the  amp power cord to a Belkin home theater surge protector 8 outlet extension cord (from Radio Shack), the vibration would start to occur in about 60 min, with initially only about 4 slow consecutive vibrations, then 5-9 slow vibration every 5-10 minutes.  This has been observed repeatedly.  So I think there is something wrong with my amp (it is more than 20 year old), although its performance is otherwise fine.   As the vibration  is delayed and reduced significantly by using the surge protector extension cord to supply the electricity to the amp,  I wonder if my electricity source is a problem. Would more expensive (presumable better) AC power cords on sale at Audiogon  solve the problem.?  
moses189
boxer12
8,654 posts
 
I'm a firm believer in fixing well built quality gear if happy with it. I have done this several times. Most recently with a Melos 222 preamp, and currently going through the same process with a single ended amp that I've owned for a number of years. The beauty of it is that you can upgrade capacitor, resistors, wire, switches, potentiometers, etc. (in the process), to bring it to a new level of performance. It can cost a fair amount of money, but usually much less than replacing with like equipment. No regrets.   
moses189 OP
23 posts
 
Thanks jobs and voxer12 for sharing. I am still puzzled as to why electrical outlet with Belkin surge protector with power  filtration reduce the speaker vibration so much. 

czarivey
5,721 posts
 
25 years old working 5 hours per week isn't too long and not too bad overall for longevity of the unit.
if you liked unit, it would be more financially wiser to overhaul it than shopping for the new or newer model unit. 
moses189 OP
23 posts
 
Thanks for sharing opinions to fix my amp. 
I did one more experiment. I switched the speaker leads to 4 ohm terminal connection on my amp.( previous early onst of vibration is with 8 ohm connection)  now The vibration did not occur until about 2 h later and was just initially 4 vibrations, followed by consecutive vibrations at 2h 40 minutes. 
Does this mean circuit board of 8 ohm is not as good as 4 ohm? Any opinion from amp experts?
thanks
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