Tube substitution for 12AX7 in an RD112

G Mac

Will it hurt my amp to substitute a 12AT7 for the 12AX7 in my RD112? I was told that it would cause the limiter channel to break up later. Thanks for any advice.

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RD 112 50

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9 years 2 months
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G Mac Mon, 10/26/2015 - 17:01

It's a 50. Thanks for replying. I have read some other posts that deal with this subject and I suspect that the 12 AT7 will be OK but any input you have is appreciated! To be clear; I know nothing about electronics and my question is coming from that perspective.

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MM 2-10-65

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10 years 9 months
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mm210 Tue, 10/27/2015 - 10:40

While I have never worked on one, I looked at the schematic and it won't hurt anything to try it. Let us know the result. Mike.

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Rory Day
Music Man Equipment
112 RD Fifty

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9 years 2 months

Rory Thu, 10/29/2015 - 12:26

A 12AX7 gives you a 100% gain factor. I have tried a 5751 which is a 70% GF. I have been using a 12AT7 which is a 60% GF for a while and it sounds great. According to the tube substitute chart found at "The Tube Store", you can go down to a 12AY7
which is a 45% GF. I have not tried this tube in my MM 112RD 50 yet. It is usually always safe to go down a couple of steps with the gain factor. It also helps you to drive the power tubes more and get more tube tone from them.

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RD 112 50

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9 years 2 months
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G Mac Mon, 11/02/2015 - 14:10

Rory-Thanks for your advice and insight. I think I'll try the 12AT7. Also, I saw your Les Paul Deluxe and your 112RD 50. Great gear! The Deluxe is my favorite LP and Music Man amps are without peer! Best to you and thanks again!

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Gary Adams
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MusicMan 212HD one thirty, purchased new february 1979.

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9 years 3 months

vettrious Tue, 12/08/2015 - 06:11

I have had good luck with JJ tubes....and also for a little diversion here and there I've used RCA black plated bottles.

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RD 112 50

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9 years 2 months
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G Mac Thu, 12/17/2015 - 15:56

I actually put in a JJ 12AX7 and it is working great! I never tried the 12AT7 that I got...the JJ works, sooo...Thanks for the advice!

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Gary Adams
Music Man Equipment
MusicMan 212HD one thirty, purchased new february 1979.

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9 years 3 months

vettrious Tue, 01/12/2016 - 01:38

As far as power tube section, JJ's seem to be the best to capture the sound of a brand new Sylvania green label in the new market and no harmonic problems.

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Tom Brown
Music Man Equipment
1 Music Man RD112 fifty and 1Music Man RD110 fifty the 110 has Python tolex while the 112 has black tolex and black grill cloth. they both have the 12ax7 tube I play mostly Rockabilly/Country and they work great. I play a Epiphone ES295 and a G&L bluesboy telecaster, they both sound great with these amps! They are my main amps. so i keep them serviced regularly. I should mention, i replaced the 112 speaker with a Celestion and it really improved the distortion on the amp. I also play in a Classic Rock band.

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9 years 8 months

TJ Sat, 01/16/2016 - 13:13

I'm looking for a replacement speaker for my 110 rd 50 just curious what your using

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RD 112 50

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9 years 2 months
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G Mac Mon, 02/01/2016 - 21:22

Thanks, vettrious! I got 2 matched JJ 6L6's from www.thetubestore.com and put them in. They're GREAT! Much better than the Groove Tube 6L6R's that were in there and less expensive. They also seem to have helped out the "mushy" that I was getting on the limiter side! Oh, that wonderful sparkly clean tone! Thanks again!

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Dustin McLaughlin
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RD50 112

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8 years 11 months

highpedality Wed, 02/03/2016 - 20:37

When switching the tubes in an RD-50 112, do you need to re-bias them or can you just pop em in and go? I have Groove Tubes now but if you guys are swearing by JJ's, I'm into checking it out. Also, does anyone here have the contact info for the Music Man guru in Ohio? Thanks!

Music Man Equipment
RD 112 50

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9 years 2 months
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G Mac Wed, 02/03/2016 - 20:54

My understanding is that the RD112 50 is a self-biasing amp. I have swapped tubes a number of times with no problem. So, just pop in the new ones and go!
I don't know about a specific guy in Ohio but, my tech is a very well versed point to point tube amp repairman that had never worked on Music Man before and he did a great job replacing the caps and troubleshooting mine. However, he was very clear about his lack of knowledge/ willingness concerning the solid state components. After some advice from mgriffin155 he checked the specs on those parts and fortunately they were good. Hopefully in the absence of said guru, you can still find someone who can do the job.Good Luck!