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Thread: Anyone With Experience with 6L6GB's in Tweed Fenders?

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    Supporting Member Zer09's Avatar
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    Anyone With Experience with 6L6GB's in Tweed Fenders?

    I've got a few pairs that do nothing but collect dust and I've always wanted to give them a try just out of curiosity. I was just wondering how far past the specs on the data sheets they can be pushed. I feel safe with plate dissipation but my concern has always been the screens. The datasheets say 270v but true to form Leo went well beyond that. Anyone who can share their experience with them?

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    Since noone has responded here is my view FWIW.

    6L6GC has Va and Vg2 ratings of 500V and an anode dissipation rating of 30W.

    6L6GB has Va rating of 360V and a Vg2 rating of 270V AND MOST IMPORTANTLY an anode dissipation rating of 19W.

    Tubes are quite tolerant of over voltage and in this case I suspect that the voltage ratings are very conservative. About the time that the 6L6GC was released tube manufacturers changed the way that they listed ratings and so the 'GB will almost certainly tolerate higher voltages. The system changed from a "Design Centre" rating system to an "Absolute Maximum" rating system. So the data an the 'GB is likely to be "Design Centre" whereas the data on the 'GC is likely to be "Absolute Maximum"

    It is that last anode dissipation rating which would concern me (even if it is a "Design Centre" value) - it would certainly require a lower bias point (lower idle current) so I would not recommend just plugging them in to see what happens.

    For some chat on tube rating systems see John Broskie Blog here:
    The Tube CAD Journal,New Mu Follower

    Hope this is of some value to you.
    Cheers,
    Ian

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    I'm using these in my 5F4 clone:

    http://www.natubes.com/data/images/p.../large_241.gif

    the plate voltage (in idle) is someting like 430V (I know, I have an out-of-spec PT, should be 410V), the screens are the same (I have a choke between them, as in 5F6 bassman)

    of course, in full tilt the B+ sags to something like 380V, so I guess it's a bit easier on the tubes. (and yes, I like playing the amp in full tilt, either using attenuator or rocking flat out)

    I wouldn't worry about the dissipation either, these particular tubes have much bigger plates than, say, real 5881's. I bias them as if they had 23W plate dissipation rating

    I also used these for years, http://natubes.com/data/images/product/large_243.gif
    also no problems whatsoever

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    Supporting Member Zer09's Avatar
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    Thanks to both of you. I feel much more comfortable trying them now. I'm using 5881's right now with 400v on both plates and screens. It was the screens I was concerned about but it sounds like I should be fine. I'm not expecting any magic from them or anything but I'd hate to see good NOS tubes go to waste.

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