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RCA BTA-1M AM Transmitter Rescue 8/25/16

Discussion in 'Amplitude Modulation' started by N6YW, Aug 25, 2016.

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  1. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Greetings to all...
    Tomorrow morning, I am venturing down the road to Wilcox Arizona to retrieve a gift.
    Literally, a gift, as in free. A complete RCA BTA-1M in questionable working condition, unmodified
    as I can see from the couple of photos I saw of the tank circuit, and has some spare parts.
    It contains all of the tubes including (4) 833A's which are simply wonderful.
    From what I can tell, this does not have the accordion style doors I had hoped for, but still a very
    cool transmitter. Lot's of 807's!
    I am going to provide a trip report complete with photos and descriptions sort of like what used to
    be posted on a formerly popular AM site, but here we have no posting police with overly starched
    underwear to interfere.
    One of the cool things about this type of vintage transmitter is that it's easy to get into space wise,
    and it's not a Tetrode design, and in the famous words of Dennis W7TFO, in a Triode, no one can
    hear you Screen! Yes, Triodes. The 833A. A beautiful tube and is so wonderful to look at when lit
    and even better when fully modulated. As such, there is a simpler power supply scheme.
    This transmitter is "Screaming" to be put on 160 meters and I may make it available to someone
    willing to make the trip to Tucson. We can talk about it.
    One thing is for sure, it's heavy but worth the trip. It needs work but it's complete and most of all,
    it says RCA on the front, so the cool factor is immense as such is the weight.
    Making room for it in the garage tomorrow as well, so I have my work cut out but again, worth it.
    More to follow...
    73 de Billy N6YW
     
    KC8YLT and WZ5Q like this.
  2. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

  3. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Wheaties. LOTS of Wheaties. That is a heavy kW. Heavier than your Bauer. Heavier than a Gates kW.

    Work smart, don't pinch any Billy parts!

    73DG
     
    K9ASE and N6YW like this.
  4. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Oh I will!!! Too much to lose and so little to gain except the fun.
     
  5. WZ5Q

    WZ5Q Ham Member QRZ Page

    I like the RCA BTA-1M transmitters, their one of my favorites.
    Too bad yours doesn't have the shutter doors, they're really unique.
    Here's a few shots of mine on its way home, the Z71 was definitely squatting.
    It has all the original RCA Iron except the Plate which is UTC.
    I look forward to seeing yours Billy.

    10-BTA-1M.jpg 7-BTA-1M.jpg 12-BTA-1M.jpg 15-BTA-1M.jpg 13-BTA-1M.jpg
     
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    Very Cool, another fine piece of gear rescued from the landfill. :)
     
    W7UUU likes this.
  7. K5UJ

    K5UJ Ham Member QRZ Page

    The RCA gear is something else. The mushroom knobs and their transformers and chokes are so identifiable. My rig has what are probably the 250 watt mod. transformer and reactor versions, but they are so conservative they'll easily handle 500 w. The BTA1 cabinets are a nice size. Not too wide or high.
     
  8. K4KYV

    K4KYV Subscriber QRZ Page

    I use an identical mod transformer to yours in my HF-300 rig. It is indeed from a 250 watt BC transmitter; the one mine came from used a pair of 805s to modulate another pair. That transformer has modulated a full KW DC input up to 140% positive modulation peaks without so much as a grunt, and it's been in the rig for at least 30 years and no failure. Even after hours of use, it never warms up beyond ambient temperature.

    I have it mounted on insulators and it has built-in spark gaps across each side of the primary, so that might help. I also keep a second one as a spare.
     
  9. K5UJ

    K5UJ Ham Member QRZ Page

    Mine are up on ceramic tiles and I've also got the spark gaps. Adjusted them as best I could according to instructions I read somewhere. That iron in the BTA1 looks like it could handle 2500 watts.
     
  10. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Well.
    What a day. A beautiful drive complete with the splendor of the cooler temps and usual awesome Arizona landscape,
    further buttressed by the late Summer Monsoon storms that pop up like mushrooms on a cow pie.
    Leaving Tucson I had that usual feel of excitement when embarking on a radio related journey. Nervous bliss
    with speckles of doubt thrown in for good measure. A balanced mindset... mind you.
    It has been decades since I have made this drive and it felt wonderful as the landscape filled my vision.
    I was exactly where I needed to be.
    The location of the RCA BTA-1M was way outside of the city limits of Wilcox, which by my account is
    on the verge of being placed on the endangered species list... a modern day ghost town in the making.
    22 miles of one way, barely paved roads gave out to washboard dirt that included many washes in which
    to navigate through. These can become treacherous in short order when it rains.

    Once I arrived near the parcel of land I was greeted by the former owner's son, who had recently retired.
    A sailor in fact, who keeps his vessel in San Diego. Upon his Quad, he lead me to an out building that resembled
    what you might find at a transmitting site next to the tower, a shanty complete with the lean-to roof.
    He opened the door and there it was. My excitement turned to disappointment because I knew then
    that the transmitter would never make power ever again... it's a parts widow.
    I mean, if I or someone else were possessed with the drive to reinvent the wheel for this old horse it could done
    but not worth the effort. It would easily take more than a year to put nail polish on this hoof.

    So, it's going to good hands who need the parts and I am happy to announce that it will not end up in the land fill!!!
    The modulator transformer is a thing of beauty and is without a doubt the heaviest transformer I have ever lifted
    to date. What was mentioned about this mod iron being conservative is spot on. According to W7TFO, this iron is
    typical of what RCA used in many of their transmitters from the 1940's onward until the end of the line.
    Two people is all it took to load this onto the truck. The bottom plate cavity was missing from the frame, and as such,
    the former owner (SK) had the iron sitting on the concrete floor and attempted to get it going using 14 awg Romex
    for the mains! It's no wonder he couldn't get anything to work. It was sadly funny because we Hams know that experimentation
    has always been the underpinnings of our hobby but this one was bad. Sorry to say, he had no clue what he was doing.

    Tubes???
    Chock full of tubes, and a box of spares and a bunch of odds and ends that amounted to a fine haul of hard to find parts.
    Again, not in the land fill. Ordinarily I wouldn't have attempted doing this with one other person, but as it was, a very
    manageable rescue. The secret to success with this kind of operation is to plan well, and prepare for any situation.
    Tools and safety gear, lot's of tie downs and WATER!!! Drink lots of water, even if you don't think you need it.
    No snakes this time either. Kind of disappointed in that one.

    Peruse the photos. An awesome day full of excitement and work that resulted in my being able to say that another one
    was saved from the Earthly bonds of the public dump!
    Thanks for reading.
    73 de Billy N6YW IMG_3783.JPG IMG_3784.JPG IMG_3789.JPG IMG_3792.JPG IMG_3793.JPG IMG_3795.JPG IMG_3796.JPG IMG_3797.JPG IMG_3798.JPG IMG_3799.JPG
     
    W2VW, KV6O, KC8YLT and 4 others like this.

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