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Who makes decent VHF amplifiers?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by N6YFM, Jul 26, 2018.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    They made a 200W output 2m amp also...I had one.

    KC2PX used to import MM stuff a lot (he had a huge stock) back in 1980-ish. I had a lot of it, and it was quite good.

    Hans VE3CRU used to modify the MMT144/28 2m modules for 135cm (222 MHz ham band here) and sell them as MMT220/28 transverters for just a few dollars more than the original. It took changing the L.O. crystals and about a dozen other components, but evidently he could do all this in less than an hour. I had one of those, also.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    My 2m tooob amp is a pair of 4CX250Bs in push-pull. It's seen clearly from all angles in Hamnation #43. I built that back in 1979 and it still runs 1kW PEP with the original tubes. Not a difficult project, it's mostly "mechanical."

    Problem with the VHF-150, same as with my amp, is there's some "warm-up" time. You can't just turn it on cold and use it a second later. But a 5894 is probably good to go in less than 60 seconds. The 4CX250Bs take about two minutes.

    My very "first" homebrew VHF amp, which I built as a kid in 1966, was a P-P 5894 amp from the ARRL VHF Manual. I followed the instructions exactly and the damned thing put out 120W the first time I drove it (with about 4W). Bravo for a really good construction article. There was nothing in that amp that was unique, even the "butterfly" tuning caps were easy to find for $2 each or so. The socket was from E.F. Johnson and cost $5. My power transformer came from a suplus place in NJ, Vetsalco, for $5. The whole amp including the chassis and the tube cost less than $100 and got me going.:)
     
    KC8VWM likes this.
  3. KM3F

    KM3F Ham Member QRZ Page

    I neglected to mention I use a keying lead from radio to my B-2518G amplifier and do not depend on the internal RF switch. When this is done the front panel FM/SSB/CW switch has no value in either position but prefer the FM setting to eliminate any possible hang-up time for release. Also adjust the relay timing for fastest release.
    The fan runs full time when DC power is applied.
    For the fan, use a 4 inch computer fan bolted to Alum angles bolted to the outside fins.
    Favor off center to the rear 2/3 of the fins where the devices are located.
    Draw air from the top. The air will follow the fins and exit the rear and front. No fin covers are needed.
     
    Last edited: Jul 27, 2018
  4. KM3F

    KM3F Ham Member QRZ Page

    Speaking of the the 222 band, I have a SS British designed amplifier with a Pair of FETS set up on 222.
    They run 26 volts, is very Linear for SSB and runs a top of 190 watts. Can you say Huge cooling fins plus fan cooling?
    The amp and power supply are of mate designs and plug in.
    It's not a plug and play as I built the sytem but a need to know all about the system to make it work from info from the Documents for the amplifier and power supply..
    I drive the amp with a DEMI 222/10 Transverter into a pair of beams and home made power splitter.
    This make the whole station all mode on 222.
    The amplifier and power supply are built to commercial standards unlike Ham grade.
     
  5. W2WDX

    W2WDX Premium Subscriber QRZ Page

    The brick I have for FM use is a 160W KLM (PA15-160BL), which if not driven hard and hard-line switched seems to have run well for me for 10 years, even being used at purchase. I also have used 160W RF Concepts amps in the past, which I find very good and reliable.

    However, I use my Commander VHF-144 for weak-signal SSB and AM operation. Usually I run it at 900W PEP SSB and no more than 150W carrier on AM. It uses a single Eimac 3CX800A7, so I tend to run it somewhat conservatively. This assures longer life and better linearity.

    I also use a sequencer for transceiver, amp, mast-mounted pre-amplifier timing.

    I generally do not use amplifiers for UHF, instead relying on antenna gain (coupled with very low-loss feeder cable) to give me the extra reach. Big UHF directional antennas are actually quite small, so I go that route.
     
    Last edited: Jul 28, 2018
    NE3R likes this.
  6. VK4TI

    VK4TI Ham Member QRZ Page

    "]I am starting to get mildly interested in 2m weak signal and SSB, and have started
    looking into amplifiers, maybe in the 90 to 160 watt range. Of course, I am looking
    for an FM & SSB capable unit."




    perhaps if you have interest in power and price then talk to Jim , W6PQL
     
  7. N8EKT

    N8EKT Ham Member QRZ Page

    Amplifiers are usually damaged because most hams are long winded and they easily exceed the duty cycle of the amp.
    And despite popular ham practices, merely mounting a fan on a mobile amplifier does NOT make it continuous duty so this is usually why most amps are damaged.
    I used Mirage amps for many years and never once had a failure.
     
  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    A fan does help a lot.

    I have used Mirage amps for repeaters on UHF and VHF at very reduced power.

    Balls to the walls will smoke them. :eek::oops:
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    How much a fan or fans help depends entirely how they're implemented.

    In the case of the SS "brick" amps with topside heatsinks, you'd always want fans very close to the sink fins and blowing down directly on them as forcefully as possible, forcing cooling air to blow through the fins and exit front and rear. I've found this does help a great deal.

    But most of these amps don't even use copper heat spreaders, they just bolt the PA transistors directly to the aluminum sinks, and usually towards "one end" of the sinks, and not the center. It's also unknown how well machined the sinks are: Very well machined sinks (<.001" flatness) are expensive, and the method of tightening the transistors to them is almost an art. You can't solder the transistor tabs in place and then tighten them down, and you can't tighten them down first and then solder the tabs. Either process is incorrect. Using slightly too much thermal compound can make it irrelevant and can be worse than not using any.

    High powered solid state stuff is tricky. Tubes are way easier -- they're supposed to get very hot.:)
     
  10. WA4SIX

    WA4SIX Ham Member QRZ Page

    Buy surplus TV-VHF or FM broadcast junk (Like me), change out a bunch of things. Then you get a loafing Kilowatt with a $40 server power supply & other junk (Bias, TX/RX switching, proper matching & some minor engineering) along with a decent LPF.
    My 6 meter Larcan TV amp is built to do continuous duty at 1.5KW. I have a spare that could be turned into a 2M amp in a couple hours. 222, even.

    Ed
     

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