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Anyone used these before?

Discussion in 'Shock Brother's DIY Amps' started by dougsta, Apr 15, 2021.

  1. dougsta

    dougsta Tele-Meister

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    These are the Loctal base version of the old WW2 vintage 807 valve which I believe is the RF transmitter version of the 6L6.
    The codes printed on the valve are5B/254M and CV428 (Military designation)

    IMG_8434.jpg

    I have a bunch of Loctal sockets and anode top caps in the parts drawer, I got these for £5 each.

    The data sheet shows it can take 600v dc on the anode because it's taken out through a top cap, with up to 80W in a push pull pair.

    CV428.jpg

    stc 5B 254.jpg

    Interesting...

    Doug
     
    Last edited: Apr 16, 2021
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  2. Jay Jernigan

    Jay Jernigan Tele-Afflicted

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    Very interesting, indeed.
     
  3. NTC

    NTC Tele-Holic

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    I would look to make a hifi amplifier out of those. Or a Bass amp. Do you need an 80 watt guitar amp?
     
  4. dougsta

    dougsta Tele-Meister

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    I was thinking they might work well in my 'Summer project' thread.

    I'm converting a solid state Fender Frontman 212R combo into a tube amp.
     
  5. NSB_Chris

    NSB_Chris Tele-Meister

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    Fascinating! Had to google "Loctal". A lot of ... "strong opinions" out there on them. Not a lot of love shown!

    Any idea why they don't recommend cathode biasing?
    The top connection is interesting. Looks like spark plugs!

    Screen Shot 2021-04-15 at 5.16.49 PM.png
     
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  6. MickM

    MickM Poster Extraordinaire Platinum Supporter

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    If I was out and saw somebody plugged into a chicken wire covered rig similar to that, I would have to make a point of talking to them when they took a break. The look of the tubes alone would make me do it.
     
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  7. dougsta

    dougsta Tele-Meister

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    I've got a local version of a 6V6, the '7C5' and the valve in my avatar is signal pentode, a 7B7, also got some 7C6 and 7Y4.

    The top caps look like something from a '50s horror B movie.

    They recommend silicone rubber coated wire to connect the top cap.
     
  8. printer2

    printer2 Poster Extraordinaire

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    Don't forget, they were meant for RF duty not audio. Might have something to do with it.
     
  9. dougsta

    dougsta Tele-Meister

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    Here's what the wiki article says on the 807:

    "The electrically similar 6L6 was not favored by hams because high transient voltages on the anode when operating in class C could cause a flashover between pins 2 and 3 on the octal base, whereas the 807 had the anode connected to a top cap, physically distant from all the base pins."

    I try a test in an 6L6GC based output section rewired for the Loctal base and top anode.
     
  10. Musekatcher

    Musekatcher Friend of Leo's

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    You guys are always coming up with more obscure interesting stuff, I'm guessing loctal is a jam of "lock" and "octal"? Looks like they added a locking feature on the center guide, to maintain connection during vibration and motion.
     
  11. dougsta

    dougsta Tele-Meister

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    Exactly, especially for use in autos, don't want those glass tubes falling out.
    The base, on the ones I have, are much more solid feeling, I have a few octals where the glue holding the glass to the base has failed and are now quite loose.
     
  12. dougsta

    dougsta Tele-Meister

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    If I run these at lower voltage, eg 400v, then they might last 'for ever'.
    They were made in the '60s so already 'middle aged' just like me :)
     
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  13. dougsta

    dougsta Tele-Meister

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    I fabri-cobbled 2 temporary adapters today, OCTAL plug to LOCTAL socket.

    I pulled the 2 6L6GC from my Peavey Valveking 112 combo (50W 480vdc B+) and put these bad boys in, all good :)

    Only ran it for 5 mins just to check it sounded ok, just to test !!not for long term use!! due to heat build up in the adapter causing insulation to fail.



    IMG_8439.jpg
     
  14. mrriggs

    mrriggs Tele-Meister

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    I've actually used spark plug wires for top cap leads. Just make sure they are "solid-core" and not resistor wires.
     
  15. dougsta

    dougsta Tele-Meister

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    The best I could find in my bits n bobs box was an old multi meter test lead rated for 600v.
     
  16. dougsta

    dougsta Tele-Meister

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    Quick sound test of these bad boys pushed hard, Clean channel with master volume up high (DIY attenuator design by JohnH)

     
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  17. dougsta

    dougsta Tele-Meister

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    2nd test, bit cleaner, 2 files, added reverb post in Logic, rough n ready Texas shuffle inspired chops and 'Albatros'



     
  18. dougsta

    dougsta Tele-Meister

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  19. Mike_LA

    Mike_LA Tele-Afflicted

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    Humm, depends, do you need lots of Clean headroom?
    Then you need more watts.
     
  20. dougsta

    dougsta Tele-Meister

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    I'm thinking if I run these at regular 6L6 voltages for 40-50W they might last for ever
     
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