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Post subject: help with 1972 MV TR 100 watt
Posted: Mon Oct 05, 2009 10:25 pm
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Hi, this is my first post here. I am working on a MV Twin reverb 100 watter from 1972. This is absolutely the worst sounding POS I have ever played in my life. The normal channel distorts at any volume with a thin, buzzy distortion. The tremolo channel is a little better but still has break-up even at the lowest volumes.

I have pulled the chassis out and it appears that the amp is un-modified. I measured about 450 plate volts on the power tubes. All the heater voltages are correct. And it has a complete new set of JJ tubes. I replaced the first driver tube with a new Tung-Sol and no change. I have not had time to do any more diagnostic work yet so I'm hoping for some suggestions on this. I will go though and measure all the voltages on the tubes, check for dc on the pots, check the trannys for shorts and etc.

Since this is my first post I would like to say thank you for any help in advance.

Bigampdaddy


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Post subject:
Posted: Tue Oct 06, 2009 1:42 pm
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It's way over due for a recap. I have a 76 and it's clean till ear splitting levels.


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Posted: Tue Oct 06, 2009 9:32 pm
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Yeah, if you're confident the tubes are fine, then I'd consider the filter caps and bias cap history. Then I'd do the voltage tests because the B+ and C- should be clean supply rails. I have a hard time suspecting output transformers in Twins of the BF&SF era, they were built like tanks. It's worth checking, of course, but if you go through the entire circuit and still have a crackling, that's when I'd send it out for a Hi-Pot test. Testing the pre amp caps for leakage is always a good idea,but it seems the noise is imposing itself on the power amp section( and possibly the pre amp). That's why I'd start with the electrolytics. ART

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