The Mullard M8080 that c-j sells is New Old Stock. A few years ago, soon after I bought my MET-1, the 6-channel preamp that uses M8080s, I bought a BUNCH of different 6C4s/6135s. Virtually all the 6C4s were highly microfonic and so bad I tossed them in the trash. I understand that the 6135 is a heavy-duty version of the 6C4, and the few I found, maybe a half-dozen, are not microfonic and sound plenty OK; I use them in the surround and SW channels. I use only the M8080s in the front-3 channels and have had NO problems with them. I have a trio that I removed from the front-3 channels after about a thousand hours that are just lying about; if you want them, they're yours for $15 Priority Mailed to you in the US. E-mail me at jeffreybehr(at)cox(dot)net if you're interested.
I hope you enjoy your c-j preamp; I sure love mine.
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