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Modifying 5F2A circuit for EZ80 and EL84

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  • Modifying 5F2A circuit for EZ80 and EL84

    Hi - this is my first post for a while - so far I've built a 5E3 and a 5E5 based amp and they're both running beautifully.

    I'm building a 5W class A amp using the Fender Princeton 5F2A as a blueprint but with an EZ80 rectifier and an EL84 power valve. (I'm in the UK).

    The PT gives out 190-0-190 and there's just one 6.3v-0 heater tap at 2A.

    Question 1: Can I run the lamp (6.3V) and all the tube heaters off the 6.3v tap (pre-amp tube is 12AX7)

    Question 2: Do I need to alter any of the resistors or caps?

    Thanks in advance

    Stephen Hartley

  • #2
    Heaters should be fine. Voltage should be ok, maybe a little low so you may not get the entire 5 watts output. You will have to change the el84 cathode resistor to get to the bias you want.

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    • #3
      Originally posted by mozz View Post
      Heaters should be fine. Voltage should be ok, maybe a little low so you may not get the entire 5 watts output. You will have to change the el84 cathode resistor to get to the bias you want.
      Thanks very much. Should I be going up or down with the cathode resistor?

      Best wishes

      Stephen

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      • #4
        Originally posted by stephenhartley View Post
        Should I be going up or down with the cathode resistor?
        Down, the AC4 uses 150 ohms.

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        • #5
          Thanks - I'll give it a go

          Cheers

          Stephen

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          • #6
            I've read that if the EZ80 blows, it will send HT through the heater circuit and blows the tubes and transformer - is it reasonable to put a 2 or 3 amp fuse into the heater circuit for protection?

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