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2 OTs?

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  • 2 OTs?

    I've been revamping a custom build and thought that 2 OTs may be the best solution for what I'm after: Tweed Deluxe/High Power - in one. I basically have my amp wired for it, however a couple things I've yet to implement.

    1-Tube rectifier going to separate B+/screen supplies in pie arrangement w/ resistor, not choke - that feeds the 2 6v6. Both filter caps 16uf. As of now the whole amp (preamp, 2 6L6, 2 6V6) is taken from a solid state rectifier w/ ample filtering and choke and the 2 6L6 are coupled via a 50w mercury OT.

    2-Additional OT for 6V6. Being a mercury dealer I'm gonna get a tweed deluxe OT for a decent price and add it. 6V6 are cathode biased and signals received from separate coupling caps from the 6L6 PA.

    Finally to overcome the "no load" issue I'm gonna run 2 speaker jacks. 1 for the 6L6 50watt PA and 1 for the 6V6 12w PA. This way there needn't be and switching on the OT primaries or secondaries. The jacks are going to be stereo jacks that, when a speaker cable is plugged in, a relay is energized and connects the power tubes cathodes to Rk/Rc. The same arrangement will be on the 6L6 tubes as well, however they're in fixed bias arrangement so their speaker jack will simply control the relay to connect the cathodes to ground. Ofcourse I will note that a speaker should be plugged in before the amp is taken off standby, in case of any flyback when the speaker plug is connected and energizes the relay/s.

    As of yet I don't see any issues w/ this idea but thought I'd see if anyone's implemented 2 OTs and if they have any foresight.

  • #2
    I was thinking about something similar, but a lot simpler for a 5E3X2. I was thinking about two OTs (Tweed Deluxe size) in parallel, with each one wired to it's own 12" speaker. I would just put a switch on one of the 6V6 tube pairs to lift the cathode ground when I wanted half power.

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    • #3
      Diablo I'd think you could simplify even more and use 1 OT and 1 speaker for that. Just get an OT w/ multiple secondary taps. When you switch to half power, also have that switch engage the next lowest tap. Unless you're concerned with the slight bias changes and/or if you want the effect of 1 less speaker when using half power. The reason I'm pursuing this is because my transformer for my high power PA is way larger than a stock tweed 5E3 OT.

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      • #4
        You're right about one OT being simpler, but what I was thinking was having it sound exactly like a 5E3 with a single 12" speaker and exactly like two 5E3s in parallel with two 12" speakers. If I use one big OT, then it may change the tone when it's operating on one pair of tubes. Who knows if that change would be better or worse, but it would be different.

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