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Thread: 6v6 and 6v6GT

  1. #1
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    6v6 and 6v6GT

    Sorry I'm a newbie here. I have a question about the 6V6 and 6V6GT version. Is the only difference between them filament warm up time? So would it be ok to swap them.

    paul

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    GT means glass tube.

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    Thank you!!

    paul

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    Noodle of Reality Steve Conner's Avatar
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    "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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    thanks to Steve:

    6V6 (steel envelope): 6V6 @ The National Valve Museum
    6V6GT (glass): 6V6G @ The National Valve Museum

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    Thanks for the link .

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    Supporting Member tubeswell's Avatar
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    In addition the 6V6GT is a beam tetrode rated for 12W plate dissipation, whereas the 6V6GTA is a pentode and can be rated up to 14W http://scottbecker.net/tube/sheets/135/6/6V6GTA.pdf
    Building a better world (one tube amp at a time)

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    Yeah I have been looking at the datasheets from National. I wanted to order some 6v6's but I would see the GT or just 6v6 listed and wasn't sure. Thanks for posting I've read a few of your other posts and they are always informative.

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    Senior Member ThermionicScott's Avatar
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    GT is a reference to the compact "bantam" tube envelope originally developed by Hytron in the late 1930's.

    It's not true that 6V6/6V6G are 12W tubes and 6V6GTA are 14W tubes. What happened is that the industry switched from the "design center" to the "design maximum" ratings system for 6V6's around the time 6V6GTA's where introduced, and most of the data sheets you find online are early examples. I have in front of me a 1960 tube manual from RCA that lists 6V6 (yes, the metal ones) and 6V6GT at 14W plate, 350V max. I am skeptical that the guts of the tube changed during this period, except for the heater.

    - Scott

    P.S. The 6V6 never changed to a pentode (implying the presence of a suppressor grid), either. It's unfortunate that GE put "beam pentode" in the linked datasheet, because there is no such thing! 6V6's were "beam tetrodes" or "beam power tubes" the whole way through.

  10. #10
    Supporting Member Jazz P Bass's Avatar
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    The "Beam Power Tube" is actually a hybrid between the tetrode & the pentode.
    The steering beams are supressor grids in a way.

  11. #11
    Senior Member ThermionicScott's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    The "Beam Power Tube" is actually a hybrid between the tetrode & the pentode.
    The steering beams are supressor grids in a way.
    Beam-forming plates serve much the same role as suppressor grids, but that doesn't make them the same thing.

    Most tube-minded people know how these tubes work, it's just the nomenclature that irks me at times. I mainly wanted to make sure it was understood that 6V6's were never reworked as true pentodes. (Why would they? That's the EL84/6BQ5's job...)

    - Scott

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    I have a couple of those 6BQ5's I haven't checked out the data on them didn't know they were pentodes. I'm still learning here as you can tell from the number of posts I have.

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    Supporting Member tubeswell's Avatar
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    Well the GE and Tung-Sol 6V6GTA datasheets have schematics of a pentodes on them (suppressor grid'n'all).

    And I didn't say they were 14W, I said they can be rated for 14W (so there) ;-b
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    Is the suppressor grid called the getter also? The little halo in the tube.

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    Supporting Member tubeswell's Avatar
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    The suppressor grid (in the schematic in the datasheet - and who knows whether it actually exists in the real world? I must pull apart an RCA 6V6GTA and see for myself) is connected to the cathode internally. Suppressor grids in pentodes are physically situated between the screen and the plate - so they are in the part of the apparatus that is enclosed by the plate. The suppressor grid is there to stop any electrons that bounce off the plate from going further back the wrong way. Whereas the getter(s) are elsewhere in the bottle (but outside of the plate structure). A getter is only used once when the bottle is first made, to de-gas the 'vacuum' inside the envelope (or if you, as a mad scientist, want to re-activate the getter in order re-vitalise a flagging tube by giving it a quick zap in a microwave oven).

    This begs the question of what's actually inside a JJ6V6S. Beam tetrode or beam pentode? The datasheet says its a pentode but...
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    Senior Member Enzo's Avatar
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    A quick look through my closest RCA copy shows all the power tubes as pentodes in the pinout drawings. 6L6, 6BQ5, 6V6, 6550, EL34, etc. I have seen data sheets with the little deflector symbols for beam elements, but I don;t see them in my RCA. And that leads me to conclude that I cannot rely upon the pinout diagram to tell me if a tube is a beam tube or a pentode. The text description does that.

    My suspicion is that in terms of the schematics, it doesn;t matter what type tube it is, and perhaps they felt it less confusing - potentially - if the element after the screen was just always drawn as a grid. SOme other data sheet issuers may have felt differently.

    And miltown, while current catalogs may offer a "6V6", unless it is a NOS offering, it won;t be a true 6V6. The metal tubes are pretty rare. I have seen darn few of those in my career. A lot fewer than I have metal 6L6s. SO if you are selecting from currently produced tubes, like EH, and JJ, and SOvtek, etc, then making a distinction between 6V6 and 6V6GT is pointless. Let's just say that current use of 6V6 is an informal use of the type name.
    Education is what you're left with after you have forgotten what you have learned.

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    Yeah I have only seen them as glass envelope tubes. That is why I really didn't understand the distinction between 6V6 and GT. I had read I think at National valve that the heater warm up time was different between the two that is why I posted that earlier. I would like to bust one open much like Tubeswell had stated. I'm picking up some tubes in Chicago this weekend that a friend had purchased from a TV repair place going out of business years ago. He said the whole bag cost him 5 bucks. There is probably 50 tubes in the bag. I know I saw the 6BQ , I didn't see any 6v6's but I also just looked into the bag when he showed it to me a few weeks ago. I grabbed a couple of boxes 6BD6,6FQ7 and some others.

  18. #18
    Senior Member ThermionicScott's Avatar
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    Once in a while, you'll see a tube diagram with [ ] brackets to indicate the beam-forming plates, but most of the time they drew it as a grid, which is admittedly confusing. You can tell whether a tube is a beam tetrode or a pentode by counting the number of grid support rods sticking up through the top mica. Pentodes will have 6 and beam tetrodes will have 4, with some flat metal tips twisted over to anchor the beam-forming plates -- same as is done for the plate. Tremo has taken some good pics of 6V6 pins here: 6V6 comparisons in Tubes Forum

    Dubious Russian/Chinese suppliers aside, I would bet a lot of money that no true pentode has been marketed as a 6V6. Even if they got the transconductance close to a real one, the curves would be a lot different.

    - Scott

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    Senior Member Enzo's Avatar
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    It pays to have the RCA book handy. The 6V6 paragraph starts out, "Metal type 6V6 and glass octal type 6V6GTA..."

    Same thing over at 6L6, "Metal type 6L6 and glass octal type 6L6GC..."


    The heater warm up time is characterized for the 6V6GTA, but not for the 6V6. They may or may not be different, the metal tube is simply not spec'd.
    Education is what you're left with after you have forgotten what you have learned.

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    Some old 6V6 tubes of various versions.


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    Your collection?

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    Quote Originally Posted by JoeM View Post
    Your collection?
    Yes, they're good used pulls that I got from a friend. He gave my 8 beer case boxes full of tubes to sort through. There are some very odd and prehistoric tubes too - I think some date back to the 1930s.

  23. #23
    Senior Member ThermionicScott's Avatar
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    Neat! I won an eBay auction a while back for about 30 misc used 6V6GT's -- I've got a picture somewhere. They all work fine, and the variation in construction is fascinating. It turns out that "real" Tung-Sol 6V6GT's used a round plate like you'd expect in a 6K6!

    - Scott

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