"AB1", "B", or "C" class for 2KW AM/FM amp.......

Discussion in 'Amateur Radio Amplifiers' started by KA5LQJ, Sep 17, 2011.

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  1. W1GUH

    W1GUH Ham Member QRZ Page

    I second that, only substitute "Apache." (The old Apache/Valiant argument. Gotta love it!)

    That power level (And the Apache puts out equivalent power -- dunno where it goes in the Valient) is good for all but the most war-like conditions in the AM window.

    And they're fun as heck to play with.
     
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    A typical Valiant will put out, on AM carrier, between 125 watts and 130 watts on 80/75. The Apache should not be run at more than about 85 watts out AM carrier on 80/75. Heath severely overrated the input power for AM on the Apache. The 6146 and 6146A/8298 are rated at 90 watts input on CW, 85 watts input on SSB, and 67.5 watts input on AM. As such, with 135 watts input and 65 percent efficiency indicates a maximum of 87.75 watts output for the 2 each 6146 or 6146A/8298 tubes in the Apache.

    Running a little bit less will definitely improve the tube life by a goodly amount.

    Also, the Apache is not known as the "scratchy Apache" for no good reason! The audio is not the best. However, by simply changing 3 capacitors in the audio chain and then unplugging the 6AL5 clipper, the audio quality is improved dramatically. Details on this at

    http://k9sth.com/uploads/Not_so_scratchy_apache.pdf

    Schematic at

    http://k9sth.com/uploads/audio_schematic_1.JPG

    One thing to remember on the Apache is that the front panel control is NOT the microphone level control. The "gain" control on the front panel controls the clipping level. The actual microphone gain control is located behind the key jack and has to be accessed with a screwdriver that has a "skinny" blade.

    For very good "stock" AM quality the WRL Globe King and Globe Champion series are good examples. I don't have a Globe King but do have a Globe Champion 350A.

    Glen, K9STH
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The 32V series from Collins (as well as the renown KW-1) also seem to have really good modulation, even unmodified. And incredibly, the tubes for those old timers are still pretty readily available.

    I always wanted a Globe King. Maybe someday.
     
  4. W1GUH

    W1GUH Ham Member QRZ Page

    Whatever the absolute values were, the relative values showed the Apache with more output power than my Valient. I wondered if there was something in the Valient that was wrong and eating up output power, so I commented about it in a QSO with another Valeint/Apache guy. He said the same thing - his Apache put out more than the Valient. I've asked about this before and never got a report of a measurement. What I've gotten is the academic theory that was presented here. Dunno the whys and wherefores of this situation.

    One thing that's pretty obvious is that the outputs of the two transmitters are so close to each other that choosing the Valient because of its 3 6146's and higher power rating is specious. The guy at the other end won't notice the difference in power output.

    As for the Apache being "scratchy"...better, and more descriptive terms would be "thin and restricted" - just like a Valient. Seems they both had that same kind of sound. And, yep, just taking out the clipper and filter in the Apache does a world of good. One thing that's easy to do with the Valient is to drive the modulator with an outboard speech amp. That helps tremendously.
     
  5. W1GUH

    W1GUH Ham Member QRZ Page

    Even the 4D32. Wow!
     
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The Valiants that I have been around easily made 125 watts + output. One thing is that the Valiant uses fixed capacitors in the antenna loading (along with a variable) and those do go bad from time to time. One, or more, of these capacitors may be the cause of the lower output.

    My Hallicrafters HT-20 also uses the 4D32. You can set it for 100 watts output, key it, then walk off for weeks at a time. It will still be putting out 100 watts when you get back!

    Also, with the HT-20 you don't have to worry about SWR. It is designed to handle impedances of at least 2000 ohms which represents an SWR of 40:1. In truth, it will match impedances a "bit" higher.

    Hallicrafters definitely made the HT-20 for continuous operation. It also covers the entire spectrum from 1500 kHz to 30 MHz.

    Glen, K9STH
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I had an Apache TX-1 built by Mike W2AJI and it worked very well (1966ish timeframe) but when I figured "AM was never coming back," I sold it in about 1968 in favor of all SSB gear. I even had the SB-10 sideband adapter for the TX-1 but that was a lot of trouble to use (multiple bandswitches, lots of carrier balancing, etc). My first SSB transmitter that I paired with a separate RX was the Marauder HX-10 and it was WAY better than the Apache except for AM work.

    I had a Valiant-II (factory built) at about the same time frame, but only for about six months. It cost a lot of money and I was a starving student and had to let it go. But it did output more power than the Apache; at least my unit did. I don't think I ever had the "original" (dark maroon) Valiant, although I've certainly seen them around a lot.

    Funny part (re AM operation) is many modern DSP rigs actually produce better quality AM than the boat anchors ever could! They're just not as fun to use.

    I set my Ten Tec Jupiter up as:

    Output 25W
    Mike gain 25%
    Compression level 2
    TX low frequency modulation cutoff 300 Hz
    TX high frequency modulation cutoff 3900 Hz
    Mike Heil PR-40

    ...and with that, checked into the local AMI net. On the scope, the rig modulates 100.0% on positive cycle, 95+% on negative cycle with extremely low distortion and full, round audio. Everybody on the net congratulated me on the best sounding boat anchor they'd heard in years.

    It took me about three check-ins before I told them it was a Ten Tec.;)
     
  8. W1GUH

    W1GUH Ham Member QRZ Page

    I suspected that multi-section fixed cap...didn't get around to it before I thinned the collection and kept ol' Scratchy.
     
  9. KM1H

    KM1H Ham Member QRZ Page


    YUK! The 300/300A/350 have horrible stock audio which is easy to understand if you look at the circuit. I have another 300 on the bench which will be finished this week with particular emphasis on the audio.

    The Viking I and II are also poor in stock form and the 32V's arent much better; I have all 3 in operating positions with improved audio. At 100W out in Class C the 6i46's in the Vik II are operating within spec and last a long time as known by many owners. I cant speak for Heathkits but my long ago experience with a DX-100 was not very good.

    One very good sounding rig is the Hallicrafters HT-9 with four 6L6s modulating a 814. It was designed before the ARRL took their aggressive stance against AM and forced manufacturers to restrict the audio to SSB standards or no more ads accepted. I happen to have a pair of those, pre and post war versions.


    Its a de TVI'd Viking I which did pretty much the same in 1946 and followed by the Vik II which had a long run.


    Granted its heavy but that didnt help them any with the government. It was Johnson who got the contract for the CD version which was called the Viking II CDC. Thats what my Viking II is and it was built in 1961, one of only 42 of both models and the last year of production. It was owned by the GM Proving Grounds club. It seems to loaf at 100W out with 100% modulation and I deliberately retained the tube rectifiers to keep voltages in spec. The audio stage is very different and reports confirm the test equipment or is it the other way around[​IMG]

    Carl
     
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