I recently finished my Spitfire build, and used a Groove Tubes 12AX7M-MPI (Matched Phase Inverter) that I bought from Revolution Guitar on ebay. Supposedly these are new builds of the Mullard style tube, with matched triode outputs for sending an equal signal to each power tube. I've read on this forum that the Spitfire and Lightning are really PP amps, so why not? A little pricey at $24.99, I guess - but , how much would a NOS matched Mullard cost?
I've been running an old ecc83 that was not matched, though reasonably close on my Eico 666, and so far I can't say it sounds any different. I'm gigging it Friday night, so I'll have a chance to listen all night in a band situation. Time will tell, or not...
I also put a GT 12AX7M in V1 (yes, a Mullard style), and I have to say the amp does sound sweeter than with the MESA 12AX7 that was in there.
So many tubes, and not enough time to try them all... Well, maybe.
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