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Is 200w enough for 75 AM in the midwest?

Discussion in 'Amplitude Modulation - AM Fans' started by K8CCA, Mar 13, 2019.

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  1. K5UJ

    K5UJ Ham Member QRZ Page

    That was then; this is now.
     
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  2. N2DTS

    N2DTS Ham Member QRZ Page

    Yes, now you have the class E guy 15 KHz away crashing your qso with 1500 watts carrier with 10 KHz audio.

    Otherwise, the band is often half empty, plenty of room often for a 100 watt qso.
    I worked Georgia from New Jersey with 3 watts on 40 meters, so I don't buy a valyant is too wimpy to get on the air with.


     
  3. K4KYV

    K4KYV Subscriber QRZ Page

    That depends on the receiver. From about 1968 to 1982 I used a National HRO, the early one with the German silver dial, built around 1935. It was excellent; the stability was superb after about a 30-minute warm-up. Good image rejection through 20m. Good sensitivity, although it did display some cross-modulation with strong signals elsewhere in the band. Selectivity was nothing to write home about, what you would expect with a couple of 455 kc/s i.f. stages and phasing type crystal filter. The dial calibration and re-settability were better than you could have ever asked for, if you made up a calibration chart for each of the plug-in coils. The chart on the front of the coil sets was virtually worthless, getting the user within the ballpark of frequency at best.

    I improved the selectivity by installing a simple, reversible modification, allowing the use of outboard mechanical filters. I put in the outboard box selectable 300~, 3.1, 4, 6, 8 and 16 kHz filters.

    The HRO had no bandspread coil for 15m since it was built before that band was ever thought about. It was very poor, hardly usable on 10m. Very poor sensitivity and it even had hand-capacity so that the frequency moved slightly when your hand approached the knob on the dial. Clearly, it was built before technology for that part of the spectrum had been fully developed.

    After using that receiver for years, in 1982 I replaced it with a 75A4. The A-4 was as superb as I had anticipated; the stability, dial calibration and frequency re-settability were far better than that of the HRO, although I didn't think the tuning knob on the A-4 had quite as solid feel as did the HRO, even with the 4:1 reduction drive. The sensitivity was about the same, but the dynamic range was better. However, the overall performance of the A-4 on the bands I used (160 through 20) didn't seem tremendously better than the HRO after I had shoe-horned in the mechanical filters.
     
  4. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    KYV:

    There were some very good to excellent receivers before the later half of the 1960s. However, the majority of amateur radio operators were using receivers that were definitely inferior and, as such, just lived with the inherent problems.

    In early 1961, when I was a junior in high school, I built a receiver that had a total of 17-tubes which covered 160-meters through 2-meters (6-meters and 2-meters were converters). For selectivity, I included a "Q" multiplier with a variable bandpass function that could take the selectivity down to under 100 Hz.

    By the time I was in Texas, I had acquired a Collins 75A-1 and a Collins 75A-2. As such, the 17-tube receiver was delegated to a supporting role. Most of the receiver can be seen in the lower left-hand corner of the following photograph:

    193b.JPG

    I still have the remains of the receiver. However, most of the parts have been salvaged to use on other projects.

    Glen, K9STH
     
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  5. N2DTS

    N2DTS Ham Member QRZ Page

    What a geek!
    Tell us about the homebrew RX!
    That was really something back then and even now!
    Looks darn nice!
     
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  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    DTS:

    My parents did not have a lot of disposable income and we were saving all that we could so that I could go to college. My father was the very first in his family to even graduate from high school (his younger brother and both younger sisters also graduated) and my mother didn't even graduate, she dropped out her junior year. In fact, of 6-children in my mother's family only 2 graduated. It was very important, to both sides, that I get a college education.

    With summer jobs, and working during Christmas vacation, I was able to obtain a used Heath DX-100 from an estate over in Illinois and K9EXE was moving and sold me his well used Hallicrafters S-85 for $25.00. However, a "top notch" receiver was out of my price range. My high school best friend, K9LHC, who's father owned several tool and die companies, had a Collins 75A-3 and I lusted over that receiver! A couple of other amateur radio operators, who lived within a mile of my parent's house, had new Heath RX-1 Mohawk receivers.

    Less than a block down the street there was a garage shop television repair facility. The owner, Orville Hartle, was a "character". He was a graduate EE but worked at the local Allis Chalmers plant, in the "tool crib", handing out hand tools to other employees. He ran the TV shop evenings and weekends and also wrote books (primarily on UFOs). Orville had a son, about a year younger than I, who had absolutely no interest in anything technical. In fact, the son didn't have an interest in just about anything. The result was that Orville, basically, adopted me.

    He kept me in as many old television chassis that I could haul off (to strip for parts) and even gave me a television for my bedroom that was better than the TV in my parent's living room! Orville encouraged me to experiment using salvaged parts (I did burn up a few transformers and other components) and also encouraged me to go on to college.

    Dave, K9BPV, who lived about 5-blocks away (he was the one who gave me my Novice Class examinations), ran a full-time TV / Radio repair shop out of his house. During that time frame, 1959 to 1962, there were a lot of the "all American 5" radio receivers around and those receivers were often needing repair. Dave had a "flat rate" for labor, plus parts, of, if I remember correctly, $3.00 per receiver to repair those units. He paid me $2.00 per radio to make the repairs and kept the other $1.00, plus the profit on the parts, for himself. Most of the repairs were just replacing a tube, or two and almost all of the remaining repairs were because the owner had tightened all the screws (alignment capacitors) trying to "improve" the performance. Working mainly on weekends, I could make between $6.00 and $8.00 per hour which was a very good wage for the time.

    Between Orville and Dave, I learned a lot about electronics and, especially, radio communications. Wanting a better receiver, but not really being able to afford such, I started reading magazine articles about building receivers. However, I could not find any individual project that would do what I wanted. But, there were features of several designs that, when combined, would probably accomplish what I wanted to accomplish. So, I gradually started work on the receiver adding, and sometimes subtracting because the circuit did not do what I wanted it to do, circuits. Finally, I got the receiver working. Unfortunately, my test equipment was not all that accurate in frequency calibration.

    To do the frequency calibration, I took the receiver over to W9IVZ who had a new Mohawk receiver along with a TX-1 Apache transmitter. Using the Mohawk as the standard, and a logging scale on the dials, I created a frequency chart for each of the amateur radio bands that the Heath equipment covered. But, the Heath equipment did not cover the 160-meter band nor the converter band for which the 6-meter and 2-meter converters worked into. For the 160-meter band I used a borrowed Heath signal generator and zero-beated stations in the AM broadcast band and then used the 2nd harmonic for the 160-meter frequency again plotting against the logging scale. For the converter band, I used a similar procedure zero-beating known frequencies and using the harmonic.

    Each band was then plotted on graph paper with the frequency on 1 axis and the logging scale on the other axis. Then, I created dials with the frequency instead of the logging scale. In fact, I wrote my 2nd article, that was published in 73 Magazine, about this process.

    By the way, Orville Hartle, since he was authoring books, encouraged me to write magazine articles of which several were sold to 73 Magazine while I was still in high school.

    Today, I probably would never even consider such a project. But, when one is in high school and when one really wants something, like Admiral David Farragut said, it is "Damn the torpedoes, full speed ahead"!

    Glen, K9STH

     
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  7. N2DTS

    N2DTS Ham Member QRZ Page

    Great story Glen!
    When I was growing up, there was no one around that I knew that had any electronics schooling so I got it all out of books from the library.
    It was not till I was about 30 years old that I had some idea what I was doing.
    But I dumpster dived and collected old TV sets to build regens and one tube transmitters and such things.

    But I want to know about the design of the RX.
    Single conversion?
    What LO type?
    Tube line up?
     
  8. K8CCA

    K8CCA Ham Member QRZ Page

    Great story Glen. You are a huge asset here! I really enjoyed reading that.
     
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  9. KM1H

    KM1H Ham Member QRZ Page


    Those tubes should get red a few times a year to keep them gettered and they are made to show modest color suh as a medium red. When they are into almost yellow then you need to back down.

    The L4B also uses chimneys so as long as the blower is turning well and the impeller blades are clean you are fine. The PS transformer is on the wimpy side so keep it under 250-300W and consider a small fan on the iron. I run a LK-500ZC that way for hours of roundtable chats; this 1986 model had improved cooling mods from the factory and still will do 1200W PEP and CW with original tubes. The various other 100-175W vintage rigs here are fine on 40-10 most of the time and even 30W is great for all over the US plus DX on 15-12-10 when the bands are hot......even with low sunspots.

    Carl
     
  10. KM1H

    KM1H Ham Member QRZ Page

    Most all the mid to higher end receivers of the 30-60's with 455-465 kc single conversion did well to at least 20M and even 15-10 with the National sliding carriage from the NC-100 to NC-240D with decent sensitivity and acceptable image rejection.
    Ones with two RF stages were often better for images but the rats nest bandswitches limited sensitivity and those single RF Nationals excelled.

    Sets such as the Hallicrafters SX-17, SX-28/32, SX-42; Hammarlund HQ-120 to 150; National NC-173/183, HRO thru HRO-50 & 50-1 all do a good to very good job plus simple mods such as plug in tube swaps really wake them up.

    Double conversion sets such as the SX-100, HQ-170/180, NC-183D, NC-300/303 are even better with excellent image rejection and better sensitivity with more modern tubes.

    Stay away from anything without a least a crystal filter for selectivity....S-20, S-40, and S-85 families, and any of the entry level sets from all sources.

    Some later models, which I wont mention for now, are built mainly for SSB and AM audio is poor to worse.

    Some of my regularly used favorites are:

    HQ-129X unmodified for 160-20M and great for BCB, the HQ-140/150 gets you to 10M
    HQ-180, SP-400X
    NC-240D, NC-183, NC-183D, NC-300, HRO-60
    SX-28, SX-73 (also R-274 & 274D versions)
    Collins 75A3 with AM filter, R-388, R-390A (a true classic boat anchor)

    Carl
     

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