Trying to find replacement valves for an oldish Musicman amp

M

Mr songwriter

New member
I've got a Musicman RD-100 head that I bought s/h about 20 years ago and as far as I can remember, I've never replaced the tubes in it. I started using it again recently and thought it might benefit from new tubes as it doesn't sound as good as it used to, especially when the bright switch is on. There are two valves that I can see in there (the amp has transistor stages too) one EL34G and one 6CA7, I've seen a few places that sell EL34's but not EL34G's, does this matter? 6CA7's seem to be fairly easily available though. I've also seen pairs of valves for sale as follows, would these do the job?

http://www.tnbstore.com.tw/photo/sovtek/eh-6ca7-el34.jpg
 
Any EL34 wll interchange. They may sound a little different, but with the Musicman's solid state preamp, it's unlikely you'll ever drive the tubes into saturation. That's where the real differences in sound emerge.

If you have one of the earlier models, with the 12AX7 in the pre, you can overdrive that...but it still doesn't affect the power amp sound.
 
Ah, thanks, those are the only two valves I can see when I take the back off, if there are any other valves in there I can't think where they would be, I've just noticed that one of them is a Sovtek as well, so I presume that EH pair would be OK.

They may sound a little different, but with the Musicman's solid state preamp, it's unlikely you'll ever drive the tubes into saturation.
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That I did not know, there is a 'distort' channel and I assumed the distortion was coming from the valves, but seemingly not, it still sounds quite nice though.

I've also just noticed that there are quite a few variants of the EL34 tubes available (JJ's, LS's, C's etc) would any of these be more suitable than any others?
 
The distortion circuit is basically what you find in a distortion foot pedal. Musicman amps, because of the solid state pre/valve power amp configuration, are very hard to drive into distortion, and were famous back in the day ('70's to early '80's) for being very clean, loud, country-rock amps. I have an early HD130 Reverb head with a 2X12 sealed cab, and it will not distort, unless I turn the preamp master up to tweak the preamp tube. I also use it for bass with a Hartke 410XL cab.

As far as tubes go, Torres Engineering always recommended Sovteks for Musicman amps, maybe because they are a dealer for that brand. I wouldn't worry about supposed "distortion" characteristics, because, as I said, there ain't gonna be much of that going on. Mine has Sovteks, and it sounds fine...with the qualification that this rig weighs a total of about 145 lb, so it stays in the studio all the time.
 
IP: thanks for the info, and you're right, they are bloody heavy. I'm looking forward to hearing what it sounds like with some new tubes in.

Edge: I'm in the UK, so it probably wouldn't be very practical, thanks anyway though.
 
I have an old HD 2x12 combo. Replaced the tubes once - just stock el34's I believe. I LOVE that amp. Ways 600lbs but man it sings. I toured the US with it - just a guitar straight in - some of the best tone I've had. And I got it for $400! Score.
 
I wonder if you know a way to fix it...

Hariossa, I took mine to a local tech. The original reverb tanks are still available, and it didn't cost that much to replace it. You can also adapt a Fender-style reverb to work with the Musicman.
 
hmm... the fender option may be avaliable here in spain, as for a tecnician, I should do some research because I don't trust anyone...
I rather do it myself to be honest, most of my guitar repairing and all circuit modifications are done by me. ;)
 
lpdeluxe said:
Musicman amps, because of the solid state pre/valve power amp configuration, are very hard to drive into distortion, and were famous back in the day ('70's to early '80's) for being very clean, loud, country-rock amps.
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funny you say that, 'cause mine starts to distort very easy, specially at low frequencies... not a good thing if you're planning to play jazz at high volume.

but this musicman amp has it's personality, here you can hear an old recording from a 4 track tape recorder:

http://www.hariossa.com/Music/Antar...ck'n'RollGirls-07-Rock'n'RollGirl-160kbps.mp3
 
I have a music man seventy five. as far as I know Music Man takes 6L6's. your amp might have been modified (or not) to take the EL34's. I would bring it to a tech and have it checked out.
 
Nice to see Music Man mentioned. I have a '79 RD50 (112) and it's been a studio-live favorite of mine for many years. I recently had some noise minor problems and had my techie check it out. The tubes were fine, just some general cleaning needed. I asked him if I should consider a new speaker and he said: "no way, don't lose this vintage sound." So I didn't.

J.
 
FALKEN said:
I have a music man seventy five. as far as I know Music Man takes 6L6's. your amp might have been modified (or not) to take the EL34's. I would bring it to a tech and have it checked out.
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Cheers for the link, FALKEN, I had a look at the (scary looking) schematic for mine (2100-RD) and I couldn't find any reference to 6L6's on it (maybe that's just the 75W model?) but there was definitely at least one EL34 on there.

Another thing that's been puzzling me is that one of the valves says "EL34G Sovtek" on it, and the other says "6CA7 EL34 USA" on it (even though that particular valve is definitely a different size (shorter and wider) than the first one) which made me wonder if another EL34 could be used as a substitute for the one marked 6CA7 ... or would that be a bad idea?
 
Mr songwriter said:
Cheers for the link, FALKEN, I had a look at the (scary looking) schematic for mine (2100-RD) and I couldn't find any reference to 6L6's on it (maybe that's just the 75W model?) but there was definitely at least one EL34 on there.

Another thing that's been puzzling me is that one of the valves says "EL34G Sovtek" on it, and the other says "6CA7 EL34 USA" on it (even though that particular valve is definitely a different size (shorter and wider) than the first one) which made me wonder if another EL34 could be used as a substitute for the one marked 6CA7 ... or would that be a bad idea?
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6CA7's and EL34's are the same tube, generally speaking, but it is better to run a matched pair. I guess it's possible that someone found a matched Sovtek EL34G and 6CA7, but I think that it is rather more likely that someone just replaced a single tube at some point. I'd recommend getting a matched pair (either 6CA7's or EL34's) and getting your bias set.
 
ggunn said:
6CA7's and EL34's are the same tube, generally speaking, but it is better to run a matched pair. I guess it's possible that someone found a matched Sovtek EL34G and 6CA7, but I think that it is rather more likely that someone just replaced a single tube at some point.
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Yes, that makes sense, I think I will go for a matched pair.

I'd recommend getting a matched pair (either 6CA7's or EL34's) and getting your bias set.
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What does getting my bias set involve? would I be better off getting a qualified amp tech to do it?
 
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