Dentron Clipperton L 572b Tubes?

Discussion in 'Amateur Radio Amplifiers' started by KE0KDQ, Oct 25, 2018.

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  1. KE0KDQ

    KE0KDQ Ham Member QRZ Page

    Rege, how do I not "overdrive the exciter" ? Some on this thread are telling me I'm not lighting the tubes in the amplifier because it needs at least 60 W drive, but why is my ALC reducing output of the 706mkII?

    ALC appears to be kicking in when I key the amp regardless of the power level on the 706mkII - I've set it at levels 5 and "H" which is 10/10. Still no luck in SSB voice--same thing happens on BPSK31 when the output without the amp is ~70 W, key the amp and power output drops off a cliff.
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The ALC is the limiter circuit in the Icom. You don't have the ALC connection to the Clipperton, so the amplifier cannot possibly have any impact on the ALC in the Icom -- the Icom is doing this itself, due to a mismatch it sees.

    An automatic tuner between the Icom and the Clipperton may not necessarily create the kind of match the Icom wants to see, to prevent its ALC from limiting output power when driving the Dentron. I tried to explain this earlier: The LDG may be setting itself up for a match at lower power, and then you try turning the power "up" on the Icom, but the LDG is still set up for lower power operation.

    That works perfectly when the load is fixed, like an antenna. It does not work perfectly when the load is variable, like an amplifier with untuned input.

    If you add the tuned input circuit to the Clipperton, this "problem" is very likely to disappear and never return.
  3. AI3V

    AI3V Ham Member QRZ Page

    Maybe there are other problems with the amp.

    After all you bought a second hand amp that arrived damaged.

    Could be just about anything

    Your posts are unclear if you get low power out of the amp, or no power at all.

  4. K0OKS

    K0OKS Premium Subscriber QRZ Page

    How about a manual tuner in between the radio and the amp, and tune it first at low power, then at full power. ??
    KD2ACO likes this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    That works. Set it up, do some tests, and write down the numbers for the bands you want to work with.

    If I was married to that amp and had to use a solid state exciter, I'd consider getting an input board of some sort, wiring it up, and be done with it.
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Yes, so would I.

    However a small manual tuner, preferably wired in close to the tube sockets with shaft extensions so it can be adjusted from outside the amp, would do the same thing, and maybe even better.

    The amp is old and has little value so I would have no hesitation about modifying it.
  7. KE0ZU

    KE0ZU Ham Member QRZ Page

    I posted the input filter assembly schematic and parts values in #28, you can't get much simpler. A piece of vector board, a toroid, a couple caps and you're set to go on any one, or all of the bands, just that simple.


    I use this amplifier with all sorts of old and new transmitters/exciters with and without auto tuners,and have had zero problems.
    KD2ACO likes this.
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Good job, and it looks nice.

    I had a Clip-L back when they were new and it lacked tuned input (but my hybrid rigs didn't care) but was a pretty solid amp -- a lot of bang for the buck, especially when Cetron was still making 52Bs.

    I know some earlier runs of Chinese 572Bs weren't too good, but understand they figured it out and now they're okay.
  9. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    You can thank the audio fools for the excess cost of the tubes. They find a tube that works for audio and it sounds "warm" then the cost skyrockets!

    Add to the fact that cheap tubes are being made that don't work as well at RF and you can get an expensive dud in your amp.

    Soft original tubes are better than some china made tubes that have a plate that does not handle the heat required for amateur radio use. I hear tyhe Russian made tubes are good, but require different bias to idle without oscillating.
  10. KE0KDQ

    KE0KDQ Ham Member QRZ Page

    KE0ZU, did you print that board yourself or purchase it somewhere?


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