Quote Originally Posted by marnold
FWIW on Jet City's website, they sell a version of the JCA20H head that they call the Comet that (besides a new baffle) has Sovtek 12AX7s and matching JJ EL84s. The site says that they chose Sovteks for "high-gain, low-noise, and long life."
That should be taken with a grain of salt. The EL84 by design is a high gain tube and power tubes in general tend not to be microphonic like preamp tubes. If they are using the Sovtek EL84M, that is the Russian mil-spec version of their EL84.