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Univox U-102 Tube Amp

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  • #16
    That it exactly.
    CC Gain stage anode load and bootstrap resistor both 100K in lieu of 250K and 40K in the Wireless World Article.

    In the last SS Amp I did with bootstrapped VAS load I found the ratio of anode (Collector) load to bootstrap resistor was important for harmonic mix. In that case 33K VA load and 22K bootstrap resistor.

    Wonder if same is true for this Jeffrey circuit?

    Cheers
    Ian

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    • #17
      The second 12AX7 triode is a Paraphase (Seesaw) Phase splitter.
      I think that (apart from bootstrapping part of the first triode's plate load) the PI essentially works as a Concertina/split-load type (the Jeffery article calles it "cathode follower PI"), and this:

      ... so 50K load at cathode too.
      ..is necessary for equal signal amplitudes at cathode and plate of the split-load PI (second triode of 12AX7).
      Last edited by Helmholtz; 11-05-2019, 08:19 PM.
      - Own Opinions Only -

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      • #18
        My Bad - I meant Cathodyne but brain short circuited and typed Paraphase.
        Cheers,
        Ian

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        • #19
          I really like the sound of the Univox U102. I had a guitar play over yesterday and we made some recordings of all my amps. He wants this one. I told him not for sale. So now we have to look for another one.

          Unfortunately some pops got into the recordings but you still get the amp.
          Attached Files

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