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The Amp was Working Better Than It Should Have...

Discussion in 'Shock Brother's DIY Amps' started by NTC, Nov 22, 2020 at 12:19 AM.

  1. NTC

    NTC Tele-Meister

    Mar 17, 2003
    After reading https://www.tdpri.com/threads/fender-cathodyne-phase-inverters.755580/
    several times, I decided I should remove the "Paul C." mod from my three homebrews. I finished the 5F11-ish first, which was built with the mod. After that, I unmoded the 5E7 Bandmaster. I verified it was working correctly and the amp sounded good. I decided to check the bias since I hadn't been in the amp in years - I have a new DMM and am getting used to the OT resistance method. Once I had the primary resistances, I measured the CT voltage, then one if the plate voltages. The voltages were the same! That is when I noticed the tube in that socket was not glowing and was white around where the getter metalization is - no vacuum. What is mystifying is that it sounded good at all. Of course, I couldn't turn it up - perhaps thay would have made the problem more obvious. The old tubes were JJ 6L6GCs. Now it has a pair of Sylvania 6L6WGBs biased at about 73% of max dissipation. I can't wait to turn it up...
  2. jsnwhite619

    jsnwhite619 Friend of Leo's

    Sep 10, 2013
    A few months ago I was working on a 5f11 Vibrolux clone and it turned out that only 1 tube was working at the time....I assumed it was the speaker because it was dirty as hell, but not that much quieter than it should have been. As @muchxs says, that first watt does most of the heavy lifting!
  3. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Dec 3, 2005
    It wasn't long after building my 5E7 that I tried it without one of the output tubes, just to see what it would sound like. At low volumes, you basically just have a single-ended amp. Turn it up a little more and it will start crunching up as the remaining output tube starts going in and out of cutoff. Kind of a fun sound, actually! :)
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