Princeton Reverb-ish build, a few questions

Discussion in 'Amp Tech Center' started by Diverted, Sep 16, 2019.

  1. Diverted

    Diverted Tele-Meister

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    Hi all,
    I have a few questions about a slightly modified Princeton Reverb AA1164 I'd like to build.

    1. I am planning on putting another single triode into the circuit to preamp a second channel which I will voice differently than the stock Princeton channel. So, the signal from both separate triodes will be fed into the tone stack at the junction of the 250pf and 100K resistor.
    My question: Should I put isolating resistors coming off of each triode's plate, and join them both at the tone stack?

    2. The "D" node on the power rail already supplies five separate plates. Would I be better off putting in a new, paralleled 20uf/18K resistor coming out of the C node, to supply this new triode? Or something else, along the lines of upping the capacitance of the D node electrolytic?

    Thanks!

    Here's the schematic:
    https://schematicheaven.net/fenderamps/princeton_rev_gz34_aa1164.pdf
     
  2. Phrygian77

    Phrygian77 Tele-Afflicted

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    1. You're going to affect the impedance in front of the tone stack, which will change the overall loss of the tone stack (affect gain) and change the effectiveness of the tone controls (to some degree). I wouldn't do it.
    2. I always move the cathodyne phase inverter up to the unused 'C' node. You can look at the original Super Champ schematic for inspiration if you want to add a separate 'E' node for the first gain stage.
     
    Last edited: Sep 17, 2019
  3. Diverted

    Diverted Tele-Meister

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    Thanks so much Phyrigian. I may just end up moving the PI up to the C node. I see however that B+ is listed at 320 for the C node, with 240 at the D node. Should I make any allowances for this change in voltage? Thanks for the tips!
     
  4. Phrygian77

    Phrygian77 Tele-Afflicted

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    No, except your heater to cathode voltage will be somewhat high. Not as high as a cathode follower, but you might want to use a JJ or a Sino 12AX7 to be safe.

    What power transformer and rectifier are you planning to use?
     
  5. Diverted

    Diverted Tele-Meister

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    I was looking into your suggestion, I've heard of it but never looked into it (Stokes mod).
    Anyway, as for power transformer I'm using one from Musical Power Supplies. US company, I've bought a few from him in the past and I've been happy so far.
    Going with solid state rectification, HV secondary is 325-0-325@90ma. But because I'm not using the 5v 2a winding or maxing out the 6.3 current, it's probably good for about 100ma. I've built one other SS-rectified Princeton with this transformer and biased around 60 percent I was getting around 390 on the plates.
    Just wondering if switching to the C node for the PI will give too much swing to the output tubes and make the transformer have to work a little too hard? At the configuration shown above it runs nice and cool.
    As for output transformer, also using a nice beefy OPT from the same source.

    Thanks for the help!

    Power transformer specs below:
     

    Attached Files:

  6. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    I’ve done the C node mod multiple times with zero issues. Go for it.

    Btw, 60% dissipation is kinda cold bias for a 6V6 A/B amp. If it sounds good to you that’s totally fine...but you might it a little hotter.
     
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