common input preamp tube question ?

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common input preamp tube question ?

Post by drsakky » Thu Jul 07, 2011 2:54 am

Hello, I am not sure if this is the right place to post but I have just bought a rm100 second hand , the amp has been used a lot but the seller had it retubed not too long ago with some Mullard el34's. I have since then sold the old modules and got 3 new ones ( I play high gain ) but it does not look like he changed the three 12ax7 common input tubes that are in the head on the left side. Do these have a effect on the sound they are pretty old.

To change these do you have to do any bias or is it just a matter of take them out and put new ones in, I dont know a lot about this sort of thing ?

Also what 12ax7tubes would you recomend ?


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Post by Shinozoku » Thu Jul 07, 2011 6:38 am

Pull em out, put new ones in. No biasing required.

The one closest to the guitar input is the input tube. I like a TAD 7025 or Tung Sol 12AX7 here.

After that, is the FX loop buffer. This one doesn't matter too much, but a Tung Sol will work.

The one closest to the power tubes is the phase inverter. This is the last gain stage processing the signal before the power section. I will ALWAYS recommend a nice NOS 5751 in there (Phillips, RCA, GE, etc.). Tung Sol will work though.
RM100M w/ Tung Sol 5881's
Blackface(self modded), Ultra Lead, SL+(out of commission), Ultra XL (self modded)
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Post by Ogopaiwa » Fri Sep 11, 2015 2:11 am

I read it this bad dream.

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