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D&A phantom 500 12 tube

Discussion in 'Amateur Radio Amplifiers' started by 17W1517, Jun 8, 2015.

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  1. W0AAT

    W0AAT XML Subscriber QRZ Page

    With a PROPER screen supply the 4cx250 isn't that horrible. Unregulated screen supplies gave it a bad name... especially those that just used a dropping resistor from the B+
     
  2. AI3V

    AI3V Ham Member QRZ Page

    Uh no, the 4cx250 is bad no matter what you do.

    Mine went to the crusher 20 years ago.

    Rege
     
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Collins KWS-1 used a pair of 4X150As (many have replaced those with 4CX250Bs -- mostly because they're more available) and Collins specified IMD worst case as -35 dBc.


    This has been measured more times than Carter has pills over the past 60 years and all the measurements confirm ~ -35dB IM3, with IM5 and IM7 below that.

    Of course they didn't push them very hard at all (1 kW PEP input power, maybe 550W PEP output power, in AB1).
     
  4. K7KBN

    K7KBN Ham Member QRZ Page

    In early 1958, my high school was 11QØØ82. The new electronics classroom had a brand new Halliccrafters 23-channel CB, and one bright morning the teacher Chris Delzer (ex-KØOEI, ex-K7LBQ, currently SK) was on the roof adjusting a nice, new 11-meter yagi. I was the designated operator. When he stomped on the roof 3 times, I was to announce "THIS IS ELEVEN-CUE-ZERO-ZERO-EIGHT TWO TESTING", check the SWR meter, and unkey. The rest of the class passed the word to Mr. Delzer who would then make further adjustments, move out of the immediate field, and stomp again.

    Right after the third or fourth test transmission, a voice with an unfamiliar accent said "11QØØ82, this is Zed Ess One Mike Sugar. I know you cawn't reply because this is your Citizen's Band in the States. Be advised you're putting a fine signal into Johannesburg."

    I yelled to the group at the door to tell Mr. Delzer to come on down. I explained what had happened, and his first question was: "You didn't talk to him, did you????" And I hadn't. I'd been tempted, but somehow resisted.

    I didn't get my novice license until Dec. 1959, and didn't work my first actual Africa station for about a year after that. DX path from Las Vegas to Jo'burg is tricky, or used to be.

    Never had a CB call myself.
     
    W2VW and KD2ACO like this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    Jo'burg?
    You're a better man (teenager) than I am for sure. I would have called back! :p
     
  6. RICHS

    RICHS QRZ Member

    All of this complaining about IMD numbers is useless. From all those hams who constantly complain about bad IMD numbers, I have yet to see an amplifier that these "experts" built that have IMD numbers like -50 db or less. I am still waiting to hear how to build a -50 IMD amplifier from the complainers. They don't know how to do it but they demand others comply and do it.

    By themselves, numbers mean nothing necessarily. I have heard through monitoring with good instruments ham stuff that was probably -25 IMD but it didn't sound bad at all. If it doesn't sound bad, who cares what the numbers are if you can't change them.

    If you don't know how to make an amplifier to your standards then quit complaining that somebody else doesn't do it for you.
     
    Last edited: Sep 14, 2017 at 10:47 PM
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    It's not a matter of sounding good or bad -- horrendous distortion can sound great...listen to guitar amplifiers! -- it's a matter of spectrum clogging. A signal that has an IM3 -25 dB will occupy more bandwidth and simply take up more space on the band unless signals are too weak to detect the IMD. When signals are strong, it's easy to spot a signal with bad IMD -- but not by listening "on frequency," where it will sound fine. The bigger problem occurs when IM5, IM7, IM9 etc. become gross enough to detect and they are very widely departed from the operating frequency; so again, tuning "on frequency" and listening, they'd still sound great while causing a lot of splatter off-channel.

    -50 dB TX IMD can be accomplished by introducing active, adaptive predistortion. The Anan labs "PureSignal" algorithm does that just fine. This can be implemented including a power amplifier in the loop, and hopefully there will be a variety of new-generation transceivers providing that capability; it will require monitoring the amplifier output and feeding some signal back into the rig, so this will add cost -- but probably worth it.
     
  8. AI3V

    AI3V Ham Member QRZ Page

    It's also common cathode (grid driven) with a 3 watt pep signal, and employs negative feedback to get to -35

    My dentron splatter box didn't have the nfb.

    We won't even talk about how bad grounded grid with no feedback is.

    Rege
     
  9. KM1H

    KM1H Subscriber QRZ Page

    It is quite simple to build a hollow state amp with -40+ dB 3rd (-46 dB using the ARRL's fraudulent method plus cherry picked audio frequencies) and progressively better on the others. This is with no NFB.

    The Dentron DTR-2000L is extremely clean at around -41dB and the MLA-2500 is no slouch either. The ClippertonL/QRO are also very clean when driven with only 100W. I own and use all 3 models and have a spectrum analyzer to monitor them plus the other amps in the station.

    The problem is that very few store bought exciters are clean enough to see the benefit. I happen to use a few of those good ones that are very affordable.

    Carl
     
    K5RT likes this.
  10. KM1H

    KM1H Subscriber QRZ Page


    And so did most other tetrode amps of that era. IMD issues were still way in the future.
     

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