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Thread: Power tube recomendations

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    Power tube recomendations

    Not sure if I can ask this or not moderators can remove this if need be. I am in he process of buying 4 new 6l6GC's for my Fender amp. Are there any that I should stay away from I hear Sovtek thrown around a lot as good ones I hear Groove Tube good and bad. Also looking for good distributors I really want to avoid "the bay" and I am sure there are sponsors here. RCA's,GE's,JJ's ?? Thanks for any help

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    Re: Power tube recomendations

    Which particular Fender model are you re-tubing?
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    Re: Power tube recomendations

    Fender Dual Showman 87-93 supposedly the same as The Twin has 4 6l6GCs

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    Re: Power tube recomendations

    What's the plate voltage for these amps?
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    Re: Power tube recomendations

    If I am reading the schematic correctly it is 470v. The amp calls for 6l6gc's on inside label what I am looking for is recommended manufactures and ones to avoid Thanks

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    Re: Power tube recomendations

    I do remember in my other thread you recommended Tung-Sol

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    Forum Member phantomman's Avatar
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    Re: Power tube recomendations

    Yeah, with 470 VDC at the plates you should definitely consider the sturdier STR tubes. Most of the blackfaces and early silverfaces ran about 450 to 460 volts which was fine for US-made RCA's, Westinghouse's, Sylvania's, etc but when Fender introduced the ultra-linear platforms with their 500 VDC plate voltages it became a game-changer for tubes manufactured in Eastern Europe and Asia which fall short in meeting the milspec standards of the previous American bottles. The STR (severe tube requirements) types were developed to accommodate extreme voltages commonly found in high-power audio applications.
    "When injustice becomes law then rebellion becomes duty."

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    Re: Power tube recomendations

    Thanks again that is what I will definitely do. Thanks for the heads up on the higher plate tolerances

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    Re: Power tube recomendations

    Power tubes should be installed as a matched quartet and must be properly biased for tone and tube longevity.
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    Re: Power tube recomendations

    I will be purchasing a set of four and one good thing is there is a bias setting adjustment on the outside of cabinet with specs.

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    Re: Power tube recomendations

    I don't have access to the specs but a reasonable starting point for the idle bias current might be 32.5 to 33.0 mA. If the tone is brittle and sterile-sounding, the bias is too low. Too high will result in visible red-plating. Be patient and use caution.
    "When injustice becomes law then rebellion becomes duty."

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    Re: Power tube recomendations

    Back of amp says bias to .04

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    Re: Power tube recomendations

    Its really best to bias with actually measuring the plate current and plate voltage instead of going with a spec written down somewhere since you should bias for the actual tubes going in and the voltage will vary based on your amp and the state of it's components.

    I think 6L6's are spec'ed for 30 watts max and then you want to 70% of that. Measure the voltage and if it is 470 VDC then the math is:

    (30 watts divided by 470 VDC = .0638) * .70 = .447 AMP or 44.7 mAmps.

    So at that voltage if actually measured to 470VDC, each tube should read 44.7 mAmp plate current and that would get you 21 watt plate dispersion. If your voltage actually varies from the book's 470vdc then your bias will be off. Can it be that far off, probably not, but that's just one of those things you want to know is right and fairly precise.

    If you're measuring cathode current instead of plate current, that's okay, but remember that using cathode current will get you a colder bias since it also includes the screen current. How much is the error? You'd have to measure the screen current and do the math. But is cathode current is all you got, it will just be a colder bias.

    good luck and stay healthy!

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    Re: Power tube recomendations

    Thank You

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