Other Amps

Amp tech help needed - Music Man 210RP-100 died yesterday…BUT LIV

27

But that probably has nothing to do with your amp not working, you don't do it when you replace tubes, and when you do it, you should just use a scope and adjust it to just get rid of the notch. Also note that the transistor bias is positive. Regular transistors are normally off, and the object is to turn them both on slightly to eliminate the turn-on lag that produces the notch. None of this is stuff you have to know. Just find a good tech who understands MusicMans. If you want to learn how to fix amps, this is the last circuit you want to begin with.
I keep trying to post part of a schematic, but the site won't let me. I just get the error page.

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Biily, I just tried to PM you, but got the error message too. If you have the schematic I'd be super-grateful if you could email it to me.

I just took another look inside and there are a pair of diodes topsy turvy to each other (rectifier?) with some nasty scorch marks on the board around them. I put a continuity tester across them and one of them is letting power through both ways. Could this be part of the problem?

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Deke. Take it to the doctor, man. MMs don't just want to kill you with weight and volume. They're brutal inside too. You want an experienced vet messing around in the guts of this exotic animal.

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Don't worry guys, I'm not about to actually do anything in there, I was just curious in case I missed something easy. I know not to touch anything. The probes I used were fully insulated and I was very careful.

Mojave, thanks for the link and also the previous ones. Unfortunately Fife is a bit of a poke from me, that's a whole 'nother country. I found a guy a couple of miles away who lists Music Man on his CV so hopefully he'll be able to help.

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Deke,

I didn't mean that you should go to Fife but just call Dennis. He's a good guy who can set you on the right track if all else fails.

Hope you get it all sorted out soon.

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About 25 miles south east of London. A pitifully long way from you.

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I spoke to the amp guy that's about 7 miles from me (about 1/2 mile from where I grew up). He's worked on MMs before and understands the positive bias thing. He seems to know what he's about so I'm taking her to him tomorrow after work. Wish us luck...

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SHE LIVES!!!

I picked it up yesterday and put it back in it's cab today and fired her up. Bit scary at first as it was humming in an unfamiliar way and distorting badly at low volume, but I had a little feel inside and sure enough one of the valves wasn't heating so it likely got a little dislodged in transit. Reseated that and tried again and bingo; my beautifully clean Music Man tones are back.

It was those 2 big diodes with the scorch marks around them, they are part of the power supply circuit. One of the smaller diodes along side them also had a little crack in it so he replaced those 4 as well, just to be safe. He also found a little ripple the crest of the sine wave on the scope, which he diagnosed as the big elec. caps leaking (they had leaked some horrible brown stuff out of them), so they got replaced as well.

Thanks to Dave for the recommendation, to Mojave for the useful pacair website, and of course Billy for all your input. I've kicked a few bucks Tim's way by way of a thank you.

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GDP at its best!

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Glad you're back up and running, Deke. I do like a happy ending!

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Glad you got it up and running Deke and no doubt sounding better than before. At what voltage do you run that amp?

Funnily enough, I had a lot more trouble with electrolytic caps when I lived in England and Scotland than I've ever had here in the Southwest. I've often wondered if it might be a climate issue.

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As you know the UK runs on a nominal 240v, but in truth it can come up well below that. I’ve known our mains at work go as low as 210v.

42

Hi Deke,

I thought that the grid had been lowered to 230V some years ago to standardize with most of Europe? No matter if it sometimes drops to 210V though!

So, is the nominal voltage requirement of your amp 240V with a 120V option?

Either way, with a vintage amp, particularly one with a solid state section you might want to check out something like this.

https://www.amprx.net/


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