Need help to ID Hallicrafters HT-37 VOX relay

Discussion in '"Boat Anchor" & Classic Equipment' started by WB9ENB, Mar 20, 2017.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: abrind-2
ad: Subscribe
ad: L-MFJ
ad: Left-3
  1. WB9ENB

    WB9ENB Ham Member QRZ Page

    Hi All,

    I have a HT-37 transmitter that a couple of the terminals fell off the VOX relay. I would like to replace it with
    the new style cube type relay. I would like to get the correct specifications for the relay since it is actuated by
    a tube switching circuit.

    The relay is a Potter - Brumfield MH-3665-1. From an old post here on QRZ someone had a technical catalog
    and identified it with 22K ohm coil resistance and 200 VDC. My coil is still good and I measure 10.6K ohm and
    about 95 volts across the coil when activated. Relays and sockets are available in both voltages but not the resistance.

    Would like to get the correct one the first time. Information is mixed and I cannot find anything on the 3665 number. Any help would be appreciated.

    Best Regards,
  2. W9GB

    W9GB Ham Member QRZ Page

    Ned, K7ELP provided assistance on this question in 2009 (here in QRZ Tech Forum).

    The TE Potter & Brumfield "R10" series was recommended P&B replacement/substitution.
    Mouser, Digi-Key, and Newark are distributors.

    TE P&B R10 Catalog Page
    During the 20th century, Siemens Electromechanical Components GmbH acquired Potter & Brumfield (P&B). Tyco International Ltd. acquired P&B from Siemens AG in fall of 1999.

    A decade ago, Potter & Brumfield had manufacturing facilities in Marion and Franklin, Ky.; El Paso, Texas; and Juarez, Mexico. They are now organized / sold by TE Connectivity.
    The Potter & Brumfield "MH" miniature telephone relay series was manufactured in Princeton, Indiana (HQ in 1950s).
    1952 Catalog
    Check with eBay reseller: micrental in Portland, Oregon who had NOS of this P&B series.

    MH-4993, 24 VDC, Electronics Surplus : Cleveland, OH
    Last edited: Mar 21, 2017
    N2EY likes this.
  3. WB9ENB

    WB9ENB Ham Member QRZ Page

    That is a lot of information. The 2009 post has conflicting information about the resistance of the coil. I also measure about 10K ohm.
    Toward the end of the 2009 posts it says 22K ohm max. The voltage is mentioned at 200 VDC. The HT-37 manual shows a voltage 200/305.
    I am measuring 95 VDC across coil when it is energized. This is where the confusion starts.

    The tubebooks link was very good.

    If anyone has been through this or has information specific to the MH-3665-1 Potter - Brumfield relay it would appreciated.
  4. KK6IYM

    KK6IYM Ham Member QRZ Page

    Can you simply put a resistor in series with your relay coil to get the results you are after? I have one of these transmitters, but have not used the VOX function.

  5. WB9ENB

    WB9ENB Ham Member QRZ Page

    If you are using the MOX position for transmit that VOX relay turns on. I never thought about using the resistor. It looks like it is a series circuit coming from the HV in the power supply and
    goes through the relay coil and then to the plate on the tube. I have the voltage and resistance that I measured from the coil so I will go back in and measure the current. Will look up the
    specs on the tube and see what I can come up with.

    Thanks for the suggestion Norm.
  6. W9GB

    W9GB Ham Member QRZ Page

    This exact approach, suggested by Norm, KK6IYM, was used by Harbach Electronics.
    Heathkit SB-200 Replacement T/R Relay (RY200) with new resistor

    The RY-200 is a replacement T/R relay for the Heathkit SB-200 & SB-201. It is a 2PDT relay with a 120V coil. A new mounting screw and rubber grommet is included. Also included is a new 4.7K 5W R-18 replacement. This resistor is included to replace the original R-18 (2K 7W). This resistor must be changed due to a change in coil resistance of the relay from about 2.3K to 1.4K by the relay manufacturer. This will allow the proper amount of operating bias to be applied to the tubes during transmit (~ -2VDC).
  7. WB9ENB

    WB9ENB Ham Member QRZ Page

    I like the concept of adjusting the resistance with a resistor. I did order a relay that matches the measurements I have taken.
    The HT-37 uses a 4PDT relay. I found one at Digi-key that I am going to try.

    The switching tube for the relay is 1/2 of a 12AT7.

    Thanks for the information as I can definitely use it as a model to work from.
  8. WB9ENB

    WB9ENB Ham Member QRZ Page

    The relay I ordered from Digikey matches the voltage, current, and resistance of the old relay. I also purchased a socket for the relay. Now I have to remove
    0.040 inches from the width of the socket and it will fit in the chassis hole nicely. Also have to make a small plate to hold the socket and I can use the
    original screw holes. Will make a clean installation.
  9. W4ZOR

    W4ZOR XML Subscriber QRZ Page

    How did the install work out? I jsut bought a HT-37 recently and would be very interested in the outcome, maybe a picture or two? Thanks! 73.....
  10. WB9ENB

    WB9ENB Ham Member QRZ Page

    The testing of the relay turning off and on went well. Correct voltages and resistance readings. I have not finished it yet
    due to harvest time. Looks good mounted from the top. If I remember correctly the cover from the old relay covers the new relay.

    Going to work out well. My disadvantage is that the relay area is burned due to wires falling off and shorting out. Actually
    the terminal broke off. Good thing that part is on the under side.

Share This Page

ad: elecraft