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Harvard Bias circuit question

Discussion in 'Amp Tech Center' started by gabasa, Nov 24, 2020.

  1. gabasa

    gabasa Tele-Meister

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    Hey everyone,

    I'm starting work on a 5F10 tweed Harvard build and my power transformer doesn't have the bias tap on it, so I'm going to have to get the voltage from pin 4 of my rectifier tube socket.

    I was hoping that someone here, who has some experience with this, might be able to recommend resistor and trim pot values that would work in this circuit.

    I feel like, if I follow the layout on this TDPRI page, all I'd have to do in my case is to raise the value of the 10k resistor in the bias circuit to something like 47k. Does this sound correct? What component values would you suggest?

    Since I'm using a Victoria Amps Co. Ivy League power transformer, my best-case scenario would be some clear pics of the amps guts, to mimic their wiring, but I can't seem to find any on the internet.

    Thanks in advance.
     
  2. gabasa

    gabasa Tele-Meister

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    Actually...nevermind, lol.
    I'm kind of new here, I'll start up a proper build journal in the correct DIY forum.....
     
  3. Jon Snell

    Jon Snell Tele-Holic

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    Firstly you need to consider what the AC output the HT winding is, work out what range of voltage and current will be reqiored and with a diode, series resistor tank capacitor and then further feed resistor to ground for rough stabilisation, consider the result that will be feeding the bias circuit.
    Screenshot 2020-11-25 at 09.38.08.png

    The 10D8 should be 1N4007 and 8uF capacitors would be around 10uF 160v.
     
    Wally likes this.
  4. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Harvard bias is discussed um, repeatedly, in this recent thread. :D

    If no bias tap, take a look at the ‘PR' method mentioned by @jsnwhite619. I linked to it in post #10...
     
  5. screefer

    screefer Tele-Holic Silver Supporter

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    subscribed...see you over at the Shock Bros.
    What are the specs on your PT?
     
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