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Power transformer getting too hot,low plate voltage

Discussion in 'Amp Tech Center' started by J-Turn, Mar 25, 2020.

  1. J-Turn

    J-Turn TDPRI Member

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    Has the new circuit I installed converted it to a cathode bias now?
    I lowered the plate current based on fixed bias numbers.
     
  2. Wally

    Wally Telefied Ad Free Member

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    J-turn, you should know the answer to that question. Iirc, Elpico guided you to re-wire the bias supply circuit and not the actual bias circuit that applies that voltage. So, unless I am mistaken, the amp is still fixed biased. ??? Suggestion: you might review this entire thread and make notes so that you have a firm grasp on where you started and where you are now...with all changes along the way notated. This would be the best way to learn from this thread, imho. Without this understanding, you will have simply been following a paint by numbers guide provided by those who helped.
     
  3. J-Turn

    J-Turn TDPRI Member

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    Actually I thought I did until you said those numbers are “low for cathode bias” amp. I set the bias #’s to what I believed were the most acceptable for fixed bias. 70% max safe on tube bias calculator sites.
     
  4. Wally

    Wally Telefied Ad Free Member

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    J-Turn, I owe you an apology. I got turned around and did say that the current draw was low for cathode.....I had forgotten that this is a fixed biased circuit when Imposted #116 yesterday. Sorry about that. It is a fixed biased output...as the scheme you posted in your first post in the thread showed.
     
    Last edited: Apr 15, 2020
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  5. J-Turn

    J-Turn TDPRI Member

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    Not a problem, you have been very helpful! It’s hard to keep track with multiple projects etc
     
  6. Wally

    Wally Telefied Ad Free Member

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    At least we did give up while some were thinking early on that the PT was done for, right? (;^).
     
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  7. D'tar

    D'tar Friend of Leo's

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    I saw your post Wally and IIRC there was talk of moving to cathode bias so I had to ask.

    Great job here resurrecting this circuit! Im glad you reworked the bias to eliminate the two fat resistors! Well done
     
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  8. elpico

    elpico Tele-Afflicted

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    Pretty reasonable. I'd probably make the first 5k resistor smaller the next time you have it open to give yourself more adjustment range for the future. I'm puzzled actually why you have less range than expected but it doesn't really matter, if the top 5k (the one that connects to c702) is changed to something like 2k you should get a couple more volts to work with.
     
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