Identifying external 'brick' amplifier

Discussion in 'Amateur Radio Amplifiers' started by N4FBZ, Feb 12, 2019.

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  1. N4FBZ

    N4FBZ Ham Member QRZ Page

    A few years ago, I purchased an external amp from a guy who said it was a CB amp (for a few bucks), as I had a (legitimate) project for one. Beyond saying it was for CB, that was all he knew. Recently I started looking at what I'd picked up.

    There are no identifying labels on it, although there is a place where it looks like a label USED to be. I looked up the transistor - it's one for a 70 plus watt VHF amp. The circuit (from what I can see) has bias and PTT delay for SSB use - one of the front panel switches is for FM or SSB. I checked the input and output impedance, and it's closest to 50 at 2m (still a bit high) - lower when power is applied (it also seems to have a preamp... I didn't try to re-draw the circuit, however, just poked around). The SWR is still uncomfortably high at 2m. The transistor seems fine.

    The brick looks like it's made for 2m - strip line construction (probably some stripline tuned circuits), no coils except for a couple of chokes in the relay and control circuit. I can't use it for the original purpose based on what I've found, but if it will amplify roughly 5 watts (SSB/FT8) to 70 watts, I REALLY can use that.

    Any other suggestions that could help identify this amp? It would be great to have some power out (I've always wanted to run 2m SSB).

    Thanks!

    Bob
    N4FBZ
     
  2. WB5WPA

    WB5WPA Ham Member QRZ Page

    How about a pix, Bob? It sounds like you know exactly what it is in any case ...
     
    KD8DEY likes this.
  3. N4FBZ

    N4FBZ Ham Member QRZ Page

    I'm uncertain. The input and output impedance are not what I'd expect (50 and 50)... I've wondered if I had a 440 amp.

    I'm going to try a couple of experiments and see what happens (dual band HT on low power). I will also try to get a picture or two. I just hope I don't fry the transistor!

    The impedance readings could be because the power level used to check them was so low, and thus current wasn't flowing.
     
  4. N4FBZ

    N4FBZ Ham Member QRZ Page

    I just tried it - 2m and 440. No output, although the switching worked as it should. Possibly the transistor is open. Back to the drawing board!
     
  5. WD8T

    WD8T Subscriber QRZ Page

    Well, if the guy who gave it to you said it was a CB amp it probably IS a CB amp. Test it with a couple watts on 10 meters. If it works, there you go.
     
  6. N4FBZ

    N4FBZ Ham Member QRZ Page

    The first thing I did... and I tried it again. The thing "buzzes" when I try HF on it into a 50 ohm load... and doesn't amplify. The transmit indicator on the amp flickers. It's being powered by a 23 amp power supply, so it shouldn't be a power supply issue.

    I did try 2m again, and it did provide some amplification... 4 watts to 7. (I suspect one of my cables is bad.)
     
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    No photo?

    If you can take a couple of quick pictures, outside and inside, unless the item is homebrewed, someone will be able to identify it.
     
  8. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    "Hold it closer to the screen please, it's a bit out of focus!" ;)
     
  9. W1TRY

    W1TRY XML Subscriber QRZ Page

    If it is a VHF or UHF amplifier that was thought to be an 11 meter amplifier, you're right on target with the term "brick."
    If you have an antenna analyzer you might sweep the input with it powered up and check for input match.
     
  10. N4FBZ

    N4FBZ Ham Member QRZ Page

    Look for them this weekend. Too much 'on my plate' between now and then.
     

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