Heavy metal transmitter transfer relay's.

Discussion in 'Amplitude Modulation' started by N6YW, Jul 17, 2019.

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  1. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Greetings to all
    I hope the Summer is treating you well.
    I've been away on a couple of mini vacations and glad to be back in the saddle again.
    The Collins 20V-2 Transmitter that I acquired recently, developed some issues with
    keying up, and staying keyed. The problem turns out to be the HV contactor, or,
    transfer relay. It's 63 years old and the contacts were badly burned from decades of use.
    It's the original unit and it's time to replace it.
    But here's the thing. This transmitter was designed to be left running continuously, or
    for Day/Night duty, so in essence, the transmitter wasn't designed for PTT operation,
    and eventually the relay would give up. After cleaning and resurfacing the relay, it became
    obvious the contacts won't last much longer if at all and I was right... one evening!
    That's okay because that's all I needed. A new style 3 pole/240 volt coil contactor will be
    installed sometime in the next week and hopefully it will last for a season or two.
    But in the meantime, a better and more modern approach is need, and I'm thinking
    solid state, which is what I used in my ART-13 power supply. But, I''l need 3 poles
    at 25 amps. I suppose 3 of the solid state devices could simultaneously switched but...
    Those of who employ retired BC transmitters need to be able to keep these beauties
    on the air and reliably so.
    What are your thoughts?
    Billy N6YW
  2. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hi Billy,

    Do you need 3 poles for single phase AC or are you running 3 phase power?

    I really like the SSR units with 'zero-crossing' detection.
    N6YW likes this.
  3. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Yes I do. Single phase 240 volts.
    Here’s a picture.
  4. K4KYV

    K4KYV Subscriber QRZ Page

    My Gates BC1-T uses two contactor relays to (1) turn the filaments and RF exciter on and (2) to turn on the HV plate supply to transmit. Normally in broadcast service the contactor relays would operate twice a day, or if the station stayed on all night, maybe once a week or so. Some hams who have converted these transmitters, modified the circuit so the transmit/receive changeover function is achieved with the "plate-on" contactor, which means the big relay clanks at every "over". Not only is the clank of the relay annoying, this imposes unnecessary wear and tear on the (likely unobtanium) stock plate contactor relay to activate and de-activate it at every transmission. The relay sequencing would have to be modified so that the "plate-on" switch controlled the exciter as well as the final so that the RF drive doesn't blank out the receiver, and that leaves the problem of how to tune the exciter stages and grid without activating the PA and transmitting a signal over the air. This has led some hams to tune the transmitter to one specific frequency in the band and never attempt to QSY. With mine, I can QSY at will anywhere in the band; in fact I converted the crystal oscillator stage to serve as a VFO buffer stage, leaving the transmitter capable of VFO control only, no crystals.

    The simple modification to the relay control circuitry uses an additional DPST 30-amp relay found in the junkbox. This relay coil works on 28 volts DC, which is close to the DC control voltage used for T/R relays in all the the station equipment. When the station T/R switch is switch to transmit, the +28v DC control voltage is turned on, and back to receive mode, the +28v is turned off, using only the main station T/R switch. One pole of the new relay makes and breaks the connection to the primary of the main plate transformer, and the other to the mid-voltage and low-voltage plate transformers.

    I fire up the transmitter by first pressing the "filament on" switch and let the tubes warm up. No grid drive yet, because the low voltage line is still disconnected through the DPST relay. The "plate-on" function now serves as a "ready" function. When both the filament-on and plate-on contactors are activated in the normal manner, the added third relay is what actually turns on the exciter and PA voltages when and only when the station T/R control is switched to transmit mode. If I want to check exciter tuning and grid drive without turning on the PA, I leave the "plate-on" switch in off position, and key up to transmit mode, giving me grid drive and I can adjust tuning of the low level stages. When the low level stages and grid drive are properly tuned, I press the "plate-on" switch, and now the transmitter is fully activated when the station control system is switched to transmit. This allows the PA stage to be tuned, which I normally do in low-power mode which also serves as the "tune" position. When everything is tuned up and ready to go on the air, the only thing inside the transmitter that clicks when I transmit is the extra DPST relay I added. The rest of the contactor control circuitry functions normally as they did in broadcast service. The big contactors are normally activated only when the transmitter is first turned on, and when it is finally turned off at the end of the session; the added DPST relay takes care of the switching function from receive to transmit, and is much quieter than either one of the big contactors.
    N6YW likes this.
  5. W9BHI

    W9BHI Ham Member QRZ Page

    I am using a NOsparc suppressor from ARC SUPPRESSION TECHNOLOGIES Model GGXAC1F480 across the contacts of the relay that switches the primary of the plate transformer on my Gates BC1-G.
    You have to see one in person to believe it.
    Absolutely NO sparking of the relay contacts while energizing and de-energizing the relay.
    There is a great video demonstration on their website as well as independent test data and videos on the internet.
    I tried all of the old fashioned ways to stop the arcing and nothing worked.
    The "r/c snubber" circuits are worthless.
    I opened up one of the units that I bought just to be nosey and there is quite a bit of solid state wizardry going on inside this little blue box.
    Here is a picture of the unit in my Gates.
    BTW, I have no affiliation with the company.
    Don W9BHI

    Attached Files:

    • 020.JPG
      File size:
      1.7 MB
    KD2ACO and N6YW like this.
  6. K5UJ

    K5UJ Ham Member QRZ Page

    I agree with Don BHI about the snubbers etc. not being good solutions. Tried a number of RC combinations, plus thermistors. The best solution I found was with those s.s. hockey puck relays.
    N6YW and KD2ACO like this.
  7. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hey guys, I'm not a transmitter rebuilder, but I have installed plenty of these on industrial loads (extruder motors, HVAC systems and chillers, big heating coils). I got tired of replacing bigass contactors on a system that has a constant duty (like the extruders on a record press. 20HP motor that cycles every 30 seconds all day).
    ... and was wondering if any of you guys have used them.

    Be sure to get ones that use zero crossing detection if you do order them. They are made as big as you need them (hundreds of amps if necessary).

    Sordid State Relays.

    Good ones cost as much as a decent contactor, but I've never had to replace a SSR. As Rob mentioned, it may just be 'the thing' for PTT duty.
    Last edited: Jul 18, 2019
  8. W2VW

    W2VW Ham Member QRZ Page

    First rule of modern high voltage safety.

    Do not rely on anything made of silicon for lockout.

    A retrofit including those zero crossing cubes would benefit from signage and additional old fashioned ways to open primary power.

    Personally I like handcuffs across the high voltage storage while working.
    AC0OB and KD2ACO like this.
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    ... redundant post removed

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