6F6 tune vs 6V6 tube

Discussion in 'Shock Brother's DIY Amps' started by Mongo Park, Oct 17, 2019.

  1. Mongo Park

    Mongo Park Tele-Holic

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    3657A270-EE2D-484C-9938-319519557B91.jpeg I have a few old radio tubes and would
    Like to use them in a champ build. I found that the 6f6 is close to the 6V6 but draws a little more heater current which I can deal with. I have one in a metal case and I have one that is glass and is labeled 6F6E, I can’t find info on this tube.
    Any thoughts on using these tubes in a champ build, well just one of them that is

    Cheers Ron.
     
  2. tubelectron

    tubelectron Tele-Holic

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    With a reasonable plate voltage and suitable cathode resistor, you can... Try to match as best the datasheet specs.

    AFAIR, the plate dissipation is 9W for a 6F6G instead of 12W for a 6V6G, meaning that a direct swap in a Champ of a 6V6 for a 6F6 may be dangerous for the 6F6's life, IMHO.

    -tbln
     
  3. marshman

    marshman Friend of Leo's

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    I seem to recall that some metal tubes are grounded to their exterior metal shell...can’t swear to it, but sounds important .
     
  4. Mongo Park

    Mongo Park Tele-Holic

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    Thanks I was thinking to build it to the 6F6 spec if it was wort it. Yes I think that some octal tubes work better when grounded to the metal
    Cheers Ron.
     
  5. Mongo Park

    Mongo Park Tele-Holic

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    More reading the 6F6 was the pre 6V6 so probably not worth the trouble using it for all the trouble.
     
  6. King Fan

    King Fan Friend of Leo's

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    Good research. I was just noticing Wikipedia says this under '6V6':

    Following the introduction in July 1936 of the 6L6, the potential of the scaled down version that became the 6V6 was soon realized. The lower-powered 6V6 was better suited for average home use, and became common in the audio output stages of "farmhouse" table-top radios, where power pentodes such as the 6F6 had previously been used. The 6V6 required less heater power and produced less distortion than the 6F6, while yielding higher output in both single-ended and push-pull configurations.​
     
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  7. printer2

    printer2 Poster Extraordinaire

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    The metal 6V6 has the can grounded. The 6F6 is a generation previous than the 6V6, used in about the same applications. It can use a 7k output transformer in SE at 285V, as long as the voltage is not crazy high I would not concern myself too much about it.
     
  8. Nickfl

    Nickfl Tele-Afflicted

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    Why? What about it being earlier makes it not worth the trouble?

    Octal preamp tubes came before miniture 9 pin tubes like the 12a*7 series but you still see them used today in a minority of amps because they sound good. Hell, tubes in general are outdated and came before transistors (and op amps and DSP and assorted other blasphemy)... but here we are discussing them in this forum.

    I'd give it a shot just to see how it sounded. The only real issue is you will want to go for somewhat lower voltages due to the lower max dissipation. The 6f6 datasheet I'm looking at shows it as an 11W tube with max plate voltage of 375v and max screen of 285v. So a slightly higher max plate voltage than most 6v6 datasheets, slightly lower screen voltage and slightly lower dissipation. So for your average single ended champ OT with say an 8K primary you could shoot for a B+ of about 320-330v and a plate voltage (plate to cathode) of something like 300v, maybe 20v lower on the screen, keep the dissipation under 10W and you should be good. It'll take some modification of the stock champ circuit, but nothing over the top.
     
  9. Mongo Park

    Mongo Park Tele-Holic

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    Well when you put it that way it sounds like an adventure worth trying. Thanks for the advice.
     
  10. tubeswell

    tubeswell Friend of Leo's

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    I've found a Brimar 6F6G (coke bottle glass envelope) in an antique shop a few years ago and took it home and chucked it in a SE champ-style build and it sounded nice. A little cleaner than a 6V6, and they are an 11W tube (so the bias needs to be a little cooler - all other things being equal)
     
    Last edited: Oct 18, 2019
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  11. printer2

    printer2 Poster Extraordinaire

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    Think of them as needing the heater current and grid signal of a 6L6 but with the plate dissipation and power output of a 6K6GT. I have six tubes and a couple of P-P transformers for them. A field coil speaker as well. One day I will make a period inspired amp.
     
  12. Mongo Park

    Mongo Park Tele-Holic

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    If I don’t like it it is easy to build
    It back to the original tube. And. I will have learned something.
    I can use the transformer that the tubes came from
     
  13. archetype

    archetype Fiend of Leo's

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    Many, if not most, are. Look at the data sheet and it should show the internal connection and which pin is tied to the shell. Even if that pin isn’t used or shown on the amp’s schematic, open up the amp and make sure the socket either grounds that pin or doesn’t use it at all.

    Sometimes, someone will use an unused tube socket lug as a tie point for something like, oh... B+ voltage that you’ll shake hands with if you touch the shell. :eek::eek::eek:
     
  14. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    The 6F6EG seems to be a purely philco thing. They used it for a few models as a single ended output tube in 1937, such as here in the 37-2620 radio. No Squat, No Stoop, No Squint.

    upload_2019-10-18_19-58-38.png
     
  15. printer2

    printer2 Poster Extraordinaire

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  16. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    Here the pinout from the schem above.....and a 6V6 for comparison...so it appears to be the same.
    upload_2019-10-21_16-40-30.png = upload_2019-10-21_16-45-45.png
     
    Last edited: Oct 21, 2019
  17. tubeswell

    tubeswell Friend of Leo's

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    same pinout
     
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