Here is the amp in question. Not knowing its historical value at the time, when I got it I replaced the EL34 power tubes with 6550s—which I particularly like—and installed a second master volume. Fortunately, the mods are reversible to restore it to its original spec. I've been using this gem forever, alternating it with a 1959-model JCM800. With the right guitar and pedals, I get tones very close to Van Halen's, but either way, it remains versatile for a lot of different genres. Now it's running an ECC83 Marconi, probably a Mullard.
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