Best tubes for MusicMan amp?

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Best tubes for MusicMan amp?

Postby BillB » Tue Jun 03, 2014 11:18 pm

My Music Man 112-RD Fifty is in need of tubes. I was just wondering if any of you using the same amp have suggestions for replacement tubes and where to purchase them.

Thanks,
Bill B.
BillB
 
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Re: Best tubes for MusicMan amp?

Postby LMark » Wed Jun 04, 2014 12:38 am

Bill, I'm jumping in here, even though I do not have a MM. I hope that's okay. There is a lot that I do not know, but I like to talk about tubes. A while back, I had an HD-130 model that got to sounding bad, but I discovered that the problem was in the reverb tank. Check those connections. (But I'm not necessarily trying to question that you know why you need new tubes.)

Are you replacing the output tubes, the preamp, or both? I would keep the old tubes and find a local tech if possible--someone who actually burns in and electronically matches the output tubes, especially if they are current production.

The original 7025 in the preamp, if that's what you have, might still be way better than any new production. I would keep it, on all accounts, if original, even if you replace it! The Sovtek 12AX7WC is a good, tough replacement, if you can find one. Many new Fender amps come with these in the preamp. Avoid the Sovtek WA and WB series at all costs. Junk. Many recommend 12AX7EH (Electro-Harmonix), but I have had a couple of these white-glass on me out of the clear blue. To be fair, EH does make some very good output and preamp tubes, especially the 6CA7EH.

For the 6L6GC outputs, the Sovtek 5881WXT is a really tough military grade tube. These also come stock in many newer Fender amps. They are tough, and meet or exceed 6L6GC specs, unlike the older Tung-Sol 5881s. You have to find someone who has a good reputation for matching and guaranteeing tubes. A local tech would be ideal. I have, however, had a good experience with NBS Electronics (Denver) and also TCTubes in St. Paul. I assume that neither of these is local to you.

If you are handy with soldering, you could also acquire a matched pair of Philips/ECG 6BG6GAs and make converters for them. I have done this successfully. But it is wise to have access to a tube tester to ensure that you have wired the converter correctly. You don't want a BZZZZZZZZZZZZZZTTT! The Philips/ECG 6BG6GA is a TOUGH NOS equivalent to the 6L6GC/7581A, but much much cheaper. I got mine here: http://www.vacuumtubes.com/6BG6.html.

If you have unlimited funds, get a matched pair of NOS Philips or Sylvania 6L6GCs or 7581As and be done with it!

I still think a local tech is your best bet. The 112-RD Fifty is supposed to be self-biasing, but the current draw of output tubes can vary dramatically from pair to pair--even if the pairs are matched. Current draw definitely affects tone. It's nice to be in the shop with a tech in this case, since he will usually have more than one pair to plug in for you to audit.

Hopefully, someone who visits this board lives (or has lived) close enough to you to recommend a good local tech. There may be some recommendations on a MM discussion board.

LMark
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Re: Best tubes for MusicMan amp?

Postby BillB » Wed Jun 04, 2014 7:26 am

Thanks, Mark!
Actually, there is a local tech who has been recommended to me, and I even dropped by there a couple of months ago and talked with him about my old Carvin amp. I will probably take the RD-112 it to him, and I thought I'd buy a pair of tubes that the Chet pickers recommend and take them along. It seems like Paul recommended some to me years ago, but I don't remember what they were. I got a message through Paul Moseley's son, Michael, and he said that Paul recommends JJ brand 6L6. Paul uses and rebuilds the little Music Man amps, so I may try those out.

The amp sounds fine for about 5 or 10 minutes, and then it starts to hum loudly, with or without the guitar plugged in. One of the tubes glows brightly and the other does not. I just checked the tubes, and they have no markings or brand names at all. I'd be surprised but I guess they could be originals. I've had the amp for probably 10 years, and it started acting up a year or so ago.

Thanks again!

Bill B.
BillB
 
Posts: 586
Joined: Thu Jul 15, 2010 5:44 pm

Re: Best tubes for MusicMan amp?

Postby LMark » Wed Jun 04, 2014 9:27 am

Well, Paul Moseley ought to know what sounds good. He's a terrific picker and has a great ear. Also great that you have a tech in sight.

Is the post-10-minute noise a hum or a honk? If it's a honk the tubes may be just fine, but you may have a bad capacitor in the signal chain. If it's a hum, ditto on the tubes, but you may have a bad filter cap in the power supply. If the tubes glow evenly on standby but one brightens up considerably more than the other on power-up--especially if its purple--then, yeah, tubes. But you can have all kinds of blue glows that are harmless and vary considerably from tube to tube. But the tech will know in five minutes or less.

I am curious about your tubes. Do you have an easy way to post a pic? Pure curiosity, of course.

LMark
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