Preamp tube roles in JCM600

[Tom M]

I want to try swapping the preamp tubes in my Marshall JCM600, but I forgot what position does what. There are 4 in there. I assume 1 is clean, and 2 is OD ... and AFAIK, one of them is for reverb. Anyone know?

[Jeff_H]

Re: Preamp tube roles in JCM600

V1 should be for OD, V2 for clean, V3 for Effects Loop and Reverb, V4 is your phase inverter.

You'll notice bigger differences in V1 and V2, but the phase inverter spot will have some effect also!

[Tom M]

Re: Preamp tube roles in JCM600

Thanks a bunch. !

[Tom M]

Re: Preamp tube roles in JCM600

If I put a 12AT7 in V2, would I lose any volume on the clean channel, or would I only lose preamp grit?

[JumpMarine]

Re: Preamp tube roles in JCM600

I am running JJ 12ax7's in all positions and Svetlana el 34's. It's a good combo, very smooth gain and great cleans, but overall a bit dark sounding. JeffH loves to use the NOS tubes in specific positions with great results. I'm sure that he'll post what he is using. BTW, that JCM 600 is a great amp, very under-rated. I love mine.

[Jeff_H]

Re: Preamp tube roles in JCM600

Tom -

If you lost any headroom by switching to a 12AT7 it wouldn't be much. The nice thing about AT7's and AU7's is that they are not as expensive as AX7's. You can get nice NOS Mullard and other AT7's for $20 bucks or so if memory serves. I haven't played with any of those.....YET!

I'll post up a couple of links in a minute for you to check out. There are some fine sounding pre-amp tubes out there that are new production, EH, JJ, and the new GT re-issues. I'm ordering some of the GT-m's soon to try against the NOS stock I have...and I sure hope I like them because the price is much more reasonable.

For whatever reason, I have really taken a liking to NOS tubes, and feel I get better tone out of them. YMMV.