Help identifying this old AM transmitter

Discussion in '"Boat Anchor" & Classic Equipment' started by W7UUU, Feb 11, 2019.

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  1. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    A ham friend sent me these photos of an old AM transmitter - looks to be a mix of used commercial and homebrew... I'll post the pix in two batches, since there a lot of them. I'm not 100% clear, but I believe it's TWO different racks. He didn't label them "rack 1 rack 2" but it looks that way.

    Really curious if anyone recognizes this transmitter or any of its constituent sub-chassis'

    First batch is FRONT photos - next batch will be REAR photos


    [Note: I normally post "full size" but due to the quantity, I didn't so please click on the small image to see it larger]

    Attached Files:

    K8AI likes this.
  2. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Here's more - these are the REAR photos

    Click on any small image to see larger


    Attached Files:

  3. KB7NRN

    KB7NRN Ham Member QRZ Page

    Yes, I'm seeing two or more different racks there and what looks to be more than one final. So there might actually be two transmitters.

    1st photo in second post shows a final chassis for two 813, one 813 is missing but you can see two large RF plate chokes and the empty socket in the lower right.

    Photo #4 shows what could be an Eimac 450th final chassis above and the driver chassis below.
  4. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    That's my take as well - the 813 chassis, if you look closely, has smaller tank coils - 20m or so. The one with the 450TH has what appears to be coil for 80m - possibly 160.

    Curious though if, just based on seeing the front panels, anything appears to be a commercial unit. The RCA logo is a hint, but could be he just had a logo laying around and put it on there for looks

    KA0HCP likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    This is very modern homebrew gear, probably built in the last six months or so.:p

    Actually, looks more like HB gear built in the early 1950s era.

    Nice work!
  6. N2EY

    N2EY XML Subscriber QRZ Page

    That's not a 450TH. In fact it's not even an Eimac tube.

    It's an '852. A triode from the early 1930s. So old its full name is UX852.

    What you may have there is a rather complex setup with separate finals for each band.

    There's an HRO receiver in one rack too. It has had the original front panel replaced by a rack panel; that's why there's no logos.

    I don't see a modulator anywhere.

    Some of the parts are clearly WW2 surplus.

    73 de Jim, N2EY
    Last edited: Feb 11, 2019
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  7. KD2AZI

    KD2AZI XML Subscriber QRZ Page

    UX852 - Cool! 75 watts potentially! The chassis with the 852 also uses a transformer from the 30's, though I agree the construction (at least of that chassis) is much more recent.
    Looks like a fun project.
    Last edited: Feb 11, 2019
  8. N2EY

    N2EY XML Subscriber QRZ Page

    75 watts from an 852? Check this out:

    See QST for September, 1932, starting on page 17. "Thirty Three Watts Per Dollar from a Type '52" by W6CUH.

    (The "Type '52" is the 852 tube.)

    Here are the typical maximum recommended CW operation ratings on the 852 (per tube), followed by W6CUH's operating values (in parenthesis) in the push-pull setup:

    Plate voltage - 3000 volts (4500)
    Plate current - 85 mA (112.5)
    Plate input - 255 watts (500)
    Power output - 165 watts (425)
    Plate dissipation - 100 watts (75)
    Grid current - 15 mA (50)

    The extremely high claimed efficiency (85%!) is the result of very high plate voltage and being driven very hard. Note the grid leak resistors - the driver stage grid leak is a 100 watt unit and the final stage grid leak is a 200 watt unit! When you need to develop over 1000 volts of grid bias, with grid current of 50 mils or so per tube, the wattage adds up. (Note also the 2 ohm parasitic suppressors...)

    The pictures in the archive scans aren't that great. I have the actual magazine, and the clearer pictures scare the bejeebus out of me. Not only is everything out in the open but the only insulation between the tuning capacitor shaft (which has 4500 volts on it) and the operator is the bakelite knob itself.

    OTOH, because primary keying is used, there is no B+ until the key is closed.

    Note the antenna connection. There's no link or capacitor - the single-wire feeder from the Windom-type antenna simply clips onto the tank coil. Impedance match is achieved by choosing the right tap point. What could POSSIBLY go wrong?

    And yet W6CUH used it safely, because he went on to write more articles for QST in later years.

    Some of the descriptions in the text are fun to read - and may require some translation. For example:

    "Primary keying was chosen because of its many advantages. In the first place it completely eliminates key clicks, no mean achievement with powers on the order of a kilowatt. The filter condenser is relieved of excessive peak voltages, obviating the use of a bleeder resistor, itself a large item at a voltage of 4500."

    "The plate supply itself consists of a 2 kw. transformer delivering up to 4500 volts each side of the center tap, a 10,000 volt 10 amp mercury arc with a conventional keep-alive system, and a 2 uF 12,000 volt mica filter condenser". (That's a mercury arc, not mercury vapor - with a mica filter capacitor. I don't think Mouser or Digi-Key carries them.)

    "The antenna feed line should then be clipped on the tank coil about about two turns either side of the center tap. Otherwise the application of full voltage to the Type '52's will cause the tank condenser to arc over despite its 12,000 volt rating" (I suppose he learned that the hard way).

    "RFC - 150 turns of No. 30 enameled wire space-wound on a glass toothbrush holder"

    (the scary part is that I know what all of that stuff means. I wonder what size Tungars he used in the keep-alive?)

    It must have looked really cool with the mercury arc, the Tungars, and the '52s all glowing.

    73 de Jim, N2EY
  9. K3XR

    K3XR Ham Member QRZ Page

    Will leave it to the experts to ID but safe to say it meets the definition of "HEAVY METAL".
  10. WQ4G

    WQ4G Ham Member QRZ Page

    I think I see one or maybe two recycled front panels from Hammarlund SP-series receivers in there.

    Some home brew and some re-purposed, but certainly well built. Who ever built it knew what they were doing.

    Parts pulled from military surplus gear perhaps? I have a power supply that looks similar in construction - custom made from surplus parts.

    Dan KI4AX
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