Adding a small pentode (e.g. EF86) to a dual-triode amp for a more authentic sound?

Discussion in 'Shock Brother's DIY Amps' started by Badside, Mar 6, 2020.

  1. Badside

    Badside Tele-Meister

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    The discussion about the effects of screen resistors on a 5E3 made me think about this: what if we introduced an EF86 (or other small signal pentode) before a 12AU7/12BH7 power amp to get some of that pentode overdrive that these can't deliver on their own?

    For example, this amp I'm working on (see schem below) is a 5W version of a 20W amp I built last year (except the 20W had a LTPI thanks to an extra preamp tube, what is cathodyne on this schematic was a post FX Loop recovery stage, the loop was MOSFET driven).

    Now, I'm thinking, what if I introduce an EF86 after the tone stack but before the cathodyne? Of course, that's going to be a hell lot of gain and I'll have to dump a lot of it. Or... hear me out here... what if I followed the EF86 with an interstage transformer that would act as a phase inverter?

    Or maybe I'm just crazy and this won't do what I'm thinking it would.

    Even thought about just using a dual EF86 power amp into a dummy load then drive the speaker with a Class-D module.

    [​IMG]
     
  2. Commodore 64

    Commodore 64 Friend of Leo's

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    I have an amp with a EF86 that can be cascaded or paralleled to V1A. I highly recommend giving it a try.
     
  3. Badside

    Badside Tele-Meister

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    The idea though is not to get gain out of the EF86, but to overdrive it late in the circuit to simulate power amp distortion.
     
  4. Commodore 64

    Commodore 64 Friend of Leo's

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    Ahh, yeah. I see ya. Did you crosspost this at ppwatt?
     
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