| Author | Message | ||
| Rich |
I hope someone can help me. I have a Music Man 210 75 which has just had new valves and a service this year. I have played only a few gigs with it then last night it cut in and out a few times then went dead, I left it half an hour or so then retried it, worked perfect for 3 songs then died again. Any suggestions or common problems? Help... Thanks Rich | ||
| michael kaus |
Jeez, a number of things come to mind. First off, I suppose you checked to see if the tubes stay lit. Yes, then check to see the obvious-the speakers losing signal. Try a different speaker/cab. Still the same? Try both input channels. Both dead or just one? Wiggled input jacks(they do get corroded). The output jacks CAN get corroded enough to block off(but not real common). Then we have to get into the basic electronics of the amp. THe fact that it's intermittant tells me it's PROBABLY a faulty/dirty contact or connection. It gets warm, resistance goes through the roof and the amp goes silent. You have to start with the basics and eliminate them one by one. Will be glad to help but you need to provide the above info. MIke. | ||
| Rich |
Thanks The problem occured during a gig (just what you need)it's a tough one because I basicly had to put it aside and run through the P.A. I did try all the inputs and changed leads etc. I have just ran the amp and checked the speaker lead, no probs there, I have left it on for a couple of hours, sat and played it for 10-15 minutes or so at gig volume, I just can't get it to happen again. When I had it serviced I got the guy to give it the once over, he said the thing is like new inside never been touched. I'm guessing something electronic, like you say a dirty contact or connection. | ||
| michael kaus |
These kind of things can drive you nuts. I have seen corroded jacks that pull this,bad solder joints and cracked resistors. Normally, connections are flaky, tubes and transistors are good or bad. If you have the ability and are careful(VERY), you can take the chassis out and run a constant signal through it and start tapping with a wooded dowl(NOT a pencil) or plastic probe. A lot of times, this will locate the problem. Remember, there are 700v or so flying around in there so be careful. Mike. | ||
| Rich |
Mike I thought to try that, if it was something simple or obvious I could fix it but some electronic gizmo inside I wont touch. So it's off to the amp tech today. I will let you know the outcome. Thanks Rich | ||
| Rich |
Right let's see if I can make any sense of what was done. He checked and polished all the input jacks and speaker out jacks, resoldered every joint in the power side and the output side, he said a couple of joints looked a bit sus. He basicly gave it a going over and checked every potential problem spot. I will now have to suck it and see... Thanks Rich | ||
| michael kaus |
Good luck-let us know. We'll try to help if we can. Mike | ||
| Rich |
My amp played up last night and I was able to check out the tubes. Firstly they stayed alight but the blue glow they emit when you play stopped, there was a very low sound I could just hear it, at one time there was no sound at all. Not much more I can say.. Thanks Rich | ||
| Steve Kennedy |
Hmmm.. that sounds exactly like your put the switch into the standby position. The blue glow only occurs when your high-voltage (plate voltage, B+) is applied to the tubes. Putting the amp in standby turns off the B+, so the blue glow stops. The same thing will happen if you lose B+ voltage for some other reason. THAT is where I would start looking! Is the power transformer producing the required AC at the high-voltage winding for the HV DC rectifier circuit to produce the required HV DC? I think you might have found a valuable clue... pay special attention to the high voltage but also check the other voltages as the output tubes appear to be shut-down (in cut-off or missing their high voltage B+). Steve | ||
| Rich |
It's starting to look like the output transformer. There's a local guy in Adelaide (Australia) who says he can fix it no probs, either a rewind or a complete new one with the correct spec, how much difference to the sound will it make? | ||
| Steve Kennedy |
Since the DC high voltage is fed to the output tubes' plates through the primary windings of the output transformer this could definitely be associated with your problem. What other measurements or clues lead you to believe it is the output transformer? The fact that EVERYTHING else checks out is only circumstantial evidence. You would just like to be sure before you spend the money to get it rewound, of course! If the original output transformer gets properly rewound by someone who sticks to the original type of wire, insulation and number/style of turns/winding you should be hard-pressed to hear any difference at all. Steve | ||
| Rich |
"You would just like to be sure before you spend the money to get it rewound, of course!" Yes for sure, the local tech is bench testing it with an oscilloscope, he hasn't 100% confirmed it yet as it's an intermitten thing and only fails for a few (10 or 20) seconds at a time. The output transformer guy said he could rewind it as per original or even build a better one, would a better one sound better? Not that my Music Man sounds bad or anything (best sounding amp I've ever owned) just curious.. Thanks Rich | ||
| Rich |
Got the amp back from the tech today, hopefully he has sorted out the problem. He said the wire(s)? from the output transformer to the speaker jack was suspect, it seemed to have some variable resistance. Friday night will be the test. Thanks guys for all your help, bit of luck it's been sorted. | ||
| Rich |
Gave the amp a good workout Friday night with no probs  Another test Sunday night... | ||
| Steve Kennedy |
Good News! Intermittents can sometimes be a REAL PAIN to find! Perhaps its all better now. The only way to find out is to use it! Steve | ||
| Rich |
Thanks for all the info guys My amp is running without a hitch woohoo... | ||
| Steve Kennedy (admin) |
Thanks for closing the loop. It's always good to get the final verdict and this doesn't always happen! As in many areas of life, people will be quite communicative when they need help but will fail to communicate once the problem is solved. Knowing the whole story might help someone else in the same situation. Thanks! Steve | ||
| Anthony Hennessy (franzoni) Username: franzoni Registered: 01-2008 |
i must of missed this one before when reading through the posts...i'm having a similar problem and there is a serious lack of good techs who know anything about these type of amps here in ireland..i've started to suspect the output tranny as it happens after it's been played for a while and i had a redplating issue last year that Mike helped me sort out but i believe that it can affect the transformer longterm... i've also noticed that the wires are rather brittleinside the amp and in my original problem one of the wires from the power tranny had broken away from the driver board as well...when i fixed that and did a cap job it came to life again but i'm still of the opinion that the sound has never been 100% since.... |
Tue, 03/25/2014 - 09:48
#1