RCA BTA 250K AM Broadcast TX Rochester NY AWA

Discussion in 'Amplitude Modulation' started by NW2K, Jun 16, 2021.

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  1. NW2K

    NW2K Ham Member QRZ Page

    KP4SX likes this.
  2. W3SLK

    W3SLK Ham Member QRZ Page

    A lot of transmitter there for only 250 watts!
  3. K5UJ

    K5UJ Ham Member QRZ Page

    That's an attractive rig with a lot of metering which is always great. I'm not certain but I think the mod. iron in that rig is what's in my 3-400 75 m. rig. There are two downers though: If I remember correctly, the rollers are plated wire which means they're limited, but probably fine for a certain amount of boost over 250 watts. Of course 250 watts with decent audio ain't too bad. But the other prob. is that all of the iron is bolted to the vertical plain. If you work alone as I do, getting that plate transformer out will be tricky. I do bicep curls but I can't hold that tranny with one hand. I bet on the assy. line those cabinets laid flat on their fronts so the iron could be set down on the (now horizontal) plain. when done the whole thing was tipped up. Fine but not so great in the field in a small tx hut. But if the iron bolts are welded in so the nuts can be loosened and removed leaving both hands free to lift each choke or transformer off the threads and set down then that's a big plus.
  4. W3SLK

    W3SLK Ham Member QRZ Page

    You got that right Rob. I remember seeing a transmitter that had a locator pin so that once it was on it wouldn't come off. But that iron is indeed heavy. That is the same mod iron and plate transformer that is in my ET-4336F. I need a new mod transformer for it.
  5. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Mike, what is the RCA P/N on the transformer you need?

  6. W3SLK

    W3SLK Ham Member QRZ Page

    It is listed in the manual as 900763
  7. W2VW

    W2VW Ham Member QRZ Page

    Is that how much it weighs?
    K5UJ likes this.
  8. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    I use one in my HF-300 rig. P/N XT-1690. It weighs about 50 lbs IIRC. I have used it since the early 70s to modulate up to a KW DC input @ 140% positive. It doesn't warm noticeably above ambient temperature inside the transmitter cabinet, even after several hours of operation. Those things are very conservatively rated. I have had a spare one on hand for more than 30 years and never had to use it. Mine came out of a transmitter with a pair of 805s modulating another pair of 805s. RCA used that same transformer in several editions of their 250w transmitter. Turns ratio, total primary to secondary, 1.55:1. No specs listed on the nameplate, other than maximum voltage, 2500. I normally run 2500v to the modulator, and 2000v to the final using separate supplies. UTC LS-103 50H/500 mA modulation reactor, 4 mfd coupling capacitor.
    K5UJ and WZ5Q like this.
  9. W3SLK

    W3SLK Ham Member QRZ Page

    That's pretty much it Don. The ET-4336F was the forerunner to the TecRad TX-350D. It was 'slapped' together by RCA Victor for the British for Lend/Lease, (as a matter of fact, the manual has a note in it about a meeting with a 'Lt. Regrave' of the British Admiralty). It is a pair of 813's modulated by 805's. It has a single source B+ that uses a 'Thyrite' resistor to regulate and divide the HV for the various other stages. The oscillator is an 807 that incorporates 2 roller inductors to tune it. If I can, I will try to scan the schematic. I apologize for hijacking the thread.
  10. W3SLK

    W3SLK Ham Member QRZ Page

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