23cm band 100-300w amp with 2w drive

Discussion in 'Amateur Radio Amplifiers' started by VE7KFX, Sep 26, 2019.

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  1. VE7KFX

    VE7KFX Ham Member QRZ Page

    Hello ,

    I am trying to build an EME station and I am looking for an amplifier for my sg labs transverter. Does anyone know where I could find one possibly second hand? I'd rather keep my costs down on this as I am getting married next year and my fiancee has me on a strict radio budget :p even if someone could point me in the right direction. I have searched Google and all I found were kits. I am all thumbs when it comes to building. Thank you in advance

    Cory VE7KFX
  2. VE3CGA

    VE3CGA XML Subscriber QRZ Page

    Hi Cory, I'm new to EME myself and am guessing you're looking for an amp for 1296. What kind of wattage are you looking for?
    You might try contacting some of the commercial Radio shops out there, they might have some used surplus equipment that might have been replaced with newer stuff. Being in a mountain rich environment they probably used something like that for relaying site to site.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    I would forget it if that is the case. It will be hard for you to stop. :p

    One problem with a amp that has a lot of gain, The output may start getting back into the input.

    Use very good shielded coax, If your wife will let you buy it. :rolleyes:

    Good Luck.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I sold my last 23cm homebrew amplifier a few years ago, but it would sorta do what you're looking for and wasn't all that difficult to build.

    It was a 3CX100A5 (7289) driving another one. Each stage has ~10 dB gain, so 2W in yields close to 20W out from the first stage, and ~20W in yields close to 200W out from the second stage. These are external anode air-cooled tubes and require a lot of air moving through the coolers, but I just used a 120mm muffin fan with "ductwork" to steer the air and that worked okay. The tubes are readily available cheaply on the surplus market -- zillions were used in airborne IFF systems and stuff years ago.

    B+ required is 1000-1200V, heater only requires 6V @ 1A per tube, so a reasonably small power supply will do this job. If you can find the tubes, and they're easy to find although often called many different things they actually are not (an example is an eBay seller who seems to have two unused surplus tubes at a low price and calls them "steel," which of course they aren't: https://www.ebay.com/i/323856783755...FO2kXqp3UrPEfXItraKnib_SIjLgaEWAaAtMFEALw_wcB ) the whole project costs maybe $100-$200 in parts, plus several hours labor using hand tools. This article is pretty good: https://www.robkalmeijer.nl/technie...hniek/hambladen/qst/1985/03/page14/index.html

    I built two about like that (although mine were copied from an old ARRL VHF-UHF Manual article) and simply cascaded them, with the first driving the second. Due to "thermal drift" that occurs, these amps need to be run with a lot of cooling as when they heat up, they drift out of tuning resonance and you end up with one hand on the tuning all the time to maintain output. Some, like Chip N6CA showed in a different article, replace the original finned coolers on these tubes with a homebrewed copper or brass one having water jets so deionized water can be circulated through the new cooling jackets and while I have not done that, it seems like a good idea and probably keeps everything cooler and more tuning-stable.

    Good luck!
  5. WE4E

    WE4E Premium Subscriber QRZ Page

    It's not too late, you know. :p:p:p
  6. VE7KFX

    VE7KFX Ham Member QRZ Page

    Thank you for the information I'll try to look that up. I am going to see if someone from the local club can help me build it if I go that route :)
  7. VE7KFX

    VE7KFX Ham Member QRZ Page

    Haha love her more than radio so I'll have to really wait for deals :)
  8. VE7KFX

    VE7KFX Ham Member QRZ Page

    I think I'll only need a 100w to 300w I have my basic with honours liscence so can go much higher than that anyway also love the call I still retain my ve3 call too Haha I was born in and grew up in Ontario :)

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