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Thread: ECF80 or ECF82 for AF?

  1. #1
    Supporting Member tubeswell's Avatar
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    ECF80 or ECF82 for AF?

    The literature I have found elsewhere 6U8 @ The National Valve Museum says they are RF tubes good for around 80MHz-220MHz. But does that mean they aren't any good for geetar amp pre-amps? Or can they do AF without a hitch? Or is there some aspect or quirk of adapting them to AF circuits that I should avail myself of the knowledge of? Anyone know or can help please?

    TIA
    Building a better world (one tube amp at a time)

  2. #2
    Noodle of Reality Steve Conner's Avatar
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    Yes, there is a little man inside who will unplug the heater if he detects any illegal input below 80MHz.

    I'd just try it and see what happens. I can't think of any reason why it wouldn't: people use RF tubes like the ECC88/6DJ8 for audio all the time.

    The only thing is that RF tubes are sometimes prone to oscillations because of their good RF performance, so you may need grid stopper resistors that an audio tube in the same circuit could do without. The ECC88 is certainly like this.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  3. #3
    Supporting Member tubeswell's Avatar
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    Thanks Steve.

    I note that there is no shielding (like there is in an EF86) inside the envelope in these tubes. http://r-type.org/pdfs/6u8.pdf . Do you think there would be any advantage in an external shield/retainer cover over the socket?
    Building a better world (one tube amp at a time)

  4. #4
    Noodle of Reality Steve Conner's Avatar
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    Well, do you find an advantage using a shield with other tubes like 12AX7s? These won't be any different.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    They are indeed interesting tubes! I have found few TV tubes to be REALLY useful, working as a professional. But being a geek, I've had a lot of fun tinkering with tubes deemed useless for mainstream use. EF183, EF184, PL84, ECF82, etc. - you can get a lot out of those, and spend very little for a couple on eBay.

    Here's a schematic you can work with for the ECF82. Use the datasheet to work out values for guitar, but this one works pretty well for starter. I can't remember the values I came up with, sorry!

    Jake

    http://4.bp.blogspot.com/_bXU7O6Ba3k..._PPUL_rev5.gif

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    Don't forget that the ECF82 was used in the original Vox AC15, the triode as an input pre-amp valve, and the pentode as the trem oscillator. Oscillations were AF as well.
    But please don't make them popular, then they will cost too much

  7. #7
    Supporting Member tubeswell's Avatar
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    Quote Originally Posted by jimboyogi View Post
    please don't make them popular, then they will cost too much
    Too late, you already did. ;-)
    Building a better world (one tube amp at a time)

  8. #8
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    Nooooooooooooooooooooooooooooooooooooooooooooooooooooo!

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