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Thread: Rectifiers: EZ81 in place of an EZ80 - is it possible?

  1. #1
    Senior Member slidincharlie (Carlo P)'s Avatar
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    Rectifiers: EZ81 in place of an EZ80 - is it possible?

    Hi y'all!
    I have just bought a small old Italian amp, a Meazzi Paramount.
    The label on the tubes is long gone, but luckily I have found this info on the web about its tube complement: EZ80, EL84, 12AX7. A very simple circuit.
    Now I'd like to buy an EZ80 and keep it in the spare parts box, but I have found locally only an EZ81. Are they interchangeable? May I use an EZ81 in place of an EZ80?
    According to the Duncan's tube data sheet locator they have similar specs but they are not reported each other as substitutes.
    TIA,
    Carlo Pipitone

  2. #2
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    You can use the EZ81 instead of the EZ80 if your PT can deliver the higher heater current (1A instead of 0.6A).

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    Senior Member slidincharlie (Carlo P)'s Avatar
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    Thanks Albert.
    What would happen if the PT cannot deliver enough current? Any risk for the PT itself or for the amp?
    Carlo Pipitone

  4. #4
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    B+ voltage & possibly 6.3VAC heater voltage will drop...long term, if the PT is stressed it might burn out. Give it a go & carefully measure the effect on the other secondary voltages & compare to the EZ80.

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    What MWJB said.
    The way I understand your first post, you still have a working EZ80 and want to use the EZ81 as a spare. Measure the heater voltage with the EZ80 (and the other tubes) in the amp, then measure with the EZ81. If there is no significant drop of heater voltage and the PT does not get hotter than normal (after an hour or so), you're safe.

  6. #6
    Senior Member slidincharlie (Carlo P)'s Avatar
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    Quote Originally Posted by Albert Kreuzer View Post
    What MWJB said.
    The way I understand your first post, you still have a working EZ80 and want to use the EZ81 as a spare. Measure the heater voltage with the EZ80 (and the other tubes) in the amp, then measure with the EZ81. If there is no significant drop of heater voltage and the PT does not get hotter than normal (after an hour or so), you're safe.
    Yes, you got it more or less. There is a rectifier in the amp that is supposed to be an EZ80 (the label has faded away). I want to buy a spare tube but I have only found EZ81's in an Italian site and I wonder if I can use it as a replacement in case the (supposed) EZ80 should fail. But, after all, I can buy an EZ80 somewhere else, there's no hurry...
    For one I will read voltages with the current rectifier as soon as I replace the e-lytic caps and see if everything is withins specs.
    Carlo Pipitone

  7. #7
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Just my thoughts Carlos,
    With respect to the additional 400ma of heater current, I don't know if that is a real concern or not.
    Keep in mind that the EZ81 and the EZ80 run off the same 6.3v supply as the 12AX7 and EL84.
    However, I'd be slightly more concerned with the EZ81 being a more robust rectifier then the EZ80 and with the EZ81, the actual B+, supplied to the entire amp under load, being higher then when powered by the original EZ80.
    Higher B+ will mean higher plate currents too.
    Many 15-20 watt amps have used the EZ81/6CA4... the EZ80 was used in low powered, two or three tube amps and radios where they do not require the higher current handling under a load.
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

  8. #8
    Senior Member slidincharlie (Carlo P)'s Avatar
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    Thank you guys. Previous advice as always...
    Carlo Pipitone

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