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3 4-125a for a 2 meter amp

Discussion in 'Amateur Radio Amplifiers' started by WA4SIX, Jun 4, 2015.

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  1. KA9JLM

    KA9JLM Ham Member QRZ Page

    Why not use a frontdoor glass out of a old Microwave oven ?

    Have Fun.
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    See, that's why I'll always be a blonde... I should have thought of that. I pass them up at the dump all the time. I wonder what their power supply is like?

    Thank you,
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    Now, with the mention of microwave ovens, an old crippled braincell woke up... I did some searching & since I know there are about 20 old microwaves at the dump (And I have bought a couple beers for the guy there) I think I will try to salvage power supply parts from them. I just read about 20 threads & articles about using 2 & leaving them grounded, full wave rectifying, knocking out the shunt & other stuff. This way, I can get it up & running in a few weeks. First, I have to finish my Larcan Hi/Lo 1.5KWto 6 meter conversion. I have the RF pallets done & have to tweak the 3 way funky wilkinsons. I am glad I am semi unemployed (Self employed designing aftermarket Dodge diesel products)....

    Thank you,
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    I think Tom is the microwave expert, on the forum.

    The Older ones that I have worked on had nice transformers.

    The old Magnetrons had a 3 volt filament if I remember correct.

    The HV winding would do about a amp or so. I saved a few and never did anything with them.

    The new ones have switching supplies, You can tell just by the weight.

    You can use the Iron in the old ones and rewind the transformer if needed. Some people weld battery packs with them.

    I built a Inverted with one once, and used the Filament winding as the Input. It worked, but was not very efficient. Better than a Dynamotor tho.

    Enjoy your project.
    Last edited: Jun 8, 2015
  5. WA4SIX

    WA4SIX Ham Member QRZ Page

    Yup, I'm thinking the big old Sears style. I remember 3 of them there when I went on Saturday. They had knobs on them, so they should be good.

    Thank you,
  6. AI6KX

    AI6KX Ham Member QRZ Page

    Ed, did you ever build something with the 4-125As? I have a pair of 4-65As with sockets and plate caps, just begging to go push-pull on 6 meters.
  7. WA4SIX

    WA4SIX Ham Member QRZ Page

    Nope, I never did. I got one of those job things that I truly love & spend a lot of time at. The article I was going to follow was the "2 meter stripline amplifier" from the ARRL archives. I have found amplification easier with surplus broadcast & industrial amps. I could probably throw the amp together in a week's vacation, as I have most everything needed.

  8. AI6KX

    AI6KX Ham Member QRZ Page

    I wish I had a source of those. Oh well, I think I'll just mount the sockets for all my oldies and light the filaments for now. It's still cool out and I nead a shack heater.
  9. WA4SIX

    WA4SIX Ham Member QRZ Page

    I "Think" that you could do the same 2M amp with the 65s, but with minor adjustments. I am sure that Carl or Steve will chime in. I ended up moving to Vegas & just working too much (And from home) to get into the projest. Outside of the power supply, it's more mechanical than anything. Look over the article. I am sure a link is somewhere in this thread. Even if you are mot really looking for a 2M amp, it's a really cool looking amp.

  10. KM1H

    KM1H Ham Member QRZ Page

    A pair of PP 4-125A's were a popular FAA and 2M amp from the 50's into the 70's or so. The ARRL and other circuits adapted the FAA circuit.
    I have an old FAA amp here that was used on AM when it was popular and then FM when I was doing a lot of VHF contests.
    The 4-65A and variants would be similar at reduced power plus it is full rated to 150 mHz.

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