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Help ID/specs this obscure amp? Palomar TX-300

Discussion in 'Amplifiers' started by napjerk, Aug 21, 2020.

  1. napjerk

    napjerk New Member

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    Hi everyone.

    I recently got this amp in a lot of radios/etc that I purchased. I can't find any real specs or info on it anywhere online. It appears to be an old (1980s?) 2 pill Palomar TX-300 but there's nothing I can find online about it.

    It has full heatsink fins on 3 sides, not just the bottom like TX Star amps, 3 switches on the front panel, ON, HI and RCV. It appears to work ok based on local radio checks, but I don't know if it can do SSB or AM only. I am a total newbie to amps and was hoping some of the experts here could help me out.

    Will try to attach some pictures.



    Thanks in advance,

    Mike
     

    Attached Files:


  2. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    MRF453 NPN Silicon Power Transistor, 60 W, 30 MHz, 12.5 V, MFR: Motorola Designed for power amplifier applications in industrial, commercial, and amateur radio equipment to 30 MHz. Specified 12.5 V, 30 MHz characteristics: Output power = 60 W, Minimum gain
     
    napjerk likes this.
  3. napjerk

    napjerk New Member

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    Thanks BJ radionut for the info on the internals. There's no documentation that I can find on the web for this box, so every bit helps. There's no SSB switch on the front, or do some of these auto switch internally?

    I have a couple of other old amps I'm dusting off and trying to get running, so I'll probably be back with more questions.

    Thanks,
    Mike
     
  4. nomadradio

    nomadradio Analog Retentive

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    The antenna relay, the one on the right is missing it's clear plastic dust cover.

    As if it was cutting out and someone wanted to clean the contact points, maybe?

    73
     
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  5. napjerk

    napjerk New Member

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    Yeah, when I first powered it up, it would chatter when keyed. I went in and cleaned both relays with deoxit and put the cover back on the one. That, and better power connections to a 30a PS seemed to stop the chatter. It seems to put out fairly clean AM compared to my KL203P.

    My cheapie power meter only goes to 100W and the low setting seems to peg it to 100. No idea what the high setting puts out.
     
  6. Justme

    Justme Sr. Member

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    all these designs come from the Motorola EB 63 design,
    http://www.communication-concepts.com/content/EB63A/Original_EB63_Engineering_Bulletin.pdf
    Fixed bias, allways there through a crude but effective circuit.
    The only need for a SSB switch is to add a condensator in the keying circuit to prrevent the relays from chattering and add about 0.5 second hold timee fo the relays.
    No need for if you drive it with a ham radio and dedicated PTT line.
    The original circuit from Motorola used MRF 454 80 watt transistors good for 140 watt relative clean output before the 1dB compression point.
     
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  7. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    napjerk likes this.
  8. napjerk

    napjerk New Member

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    Thanks for the information, guys. Seems like there was a bunch of companies putting out similar boxes back in the day.
     
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  9. blasphemy000

    blasphemy000 Active Member

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    The input transformer center tap appears to be connected to ground through that red air core inductor. If that's the case it's unbiased and would operate in Class-C.
     
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  10. nomadradio

    nomadradio Analog Retentive

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    In other words, built only to work for AM. Will sound like poo on sideband. It only takes a switch and a capacitor to add the delay to the relay. Keeps it from chattering since there's no carrier to hold the relay engaged. Setting up proper operating bias needed for clean sideband just adds to the cost and won't make it sell any better. You'll see that this gets left out of a lot of amplifiers.

    Got left out of this one.

    73
     
    napjerk likes this.

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