Vacuum tube based keyers

Discussion in 'Straight Keys - CW Enthusiasts' started by AA4OO, Apr 5, 2018.

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  1. AA4OO

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    I've recently been bitten by the vintage bug. I'm looking for a schematic/design or even commercially made keyer that used vacuum tube technology.

    Richard AA4OO
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  2. AA4OO

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  3. K3UJ

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  4. N2EY

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  5. N2EY

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    The "standard of reference" for hollow-state electronic keyers is the "T.O. Keyer", designed by W9TO.

    Hallicrafters made a commercial version called the HA-1. The manual is here:

    which has a ton of information about how it works. The schematic and parts list make it easy to homebrew a copy. About the only hard-to-get part is the mercury-wetted relay.

    (If you decide to homebrew one, let me know. I have many of the parts, and all the tubes).

    73 de Jim, N2EY
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  6. KD4ZFS

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    Hello Richard,

    Recently ??? I think you've been "vintage" from day one! :D
  7. K3XR

    K3XR Ham Member QRZ Page

    The Hallicrafters HA-1 was my first keyer still have it and a couple of spares. If you can find a good operating HA-1 you won't be disappointed .
  8. N2EY

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    They show up on the watery auction place pretty regularly. Perhaps get one "for parts or not working" and restore it. The usual treatments (replace all electrolytics, check all resistors and capacitors, clean all switches, pots and contacts, check tubes) are pretty straightforward.

    More info at:

    The only thing I don't like about the HA-1 is that it's a bit crowded under the chassis.

    73 de Jim, N2EY
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  9. AA4OO

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    Thanks Jim,

    There appear to be a few HA-1's on the famous auction site. I also downloaded the manual and looked at the schematic. I have a spare OA2 and 12AUX7 but my two OB2's are slotted for another project. I think the hardest part of that circuit to "homebrew" would be the power transformer. Being new to the tube world, as I try to source parts for homebrew tube stuff I get stuck trying to find appropriate power transformers and power supply chokes. There's a simple tube transmitter I'm gathering parts for ( but finding a 650V 30ma transformer and a 8Hy power supply choke are proving difficult.

    The HA-1 schematic shows the 12.6V filament requirement but I don't see a B+ voltage requirement. I'm unfamiliar with using both an OA2 and OB2 together so I don't know what the unregulated input voltage should be. I know this isn't the proper forum for homebrew or boatanchor questions. Other than my power supply questions the circuit for the keyer appears to be pretty simple. I'm actually loving the sound of the sidetone and received signals from my HW-101, so I would like to have a keyer for this 6AG7 amp project that is giving me tube sidetone as well.
  10. N2EY

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    I have a bunch of regulator tubes and a system to test them. So no worries about oB2s.

    With power transformers you can always use something with higher current ratings. Also multiple transformers. One trick for small projects is to use two heater transformers, one large and one small. The large one lights the heaters and also feeds the second one. The second one steps the heater voltage back up to 120 volts or so.

    12AU7s have a center-tapped heater so they can be lit from 12.6 or 6.3 volts.


    There are many designs which appeared in ARRL Handbooks, QST and other publications. You have to look back a bit because keyers were one of the first things to be transistorized and then done with ICs, because the circuitry is almost all logic. The use of a keying relay means that they will key almost anything.

    If you design to homebrew one - start a thread on the Boatanchor forum and lots of us will help out.

    73 de Jim, N2EY

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