W7TFO Hints & Kinks: "Fear & Loathing in the land of Engineering"

Discussion in 'Amplitude Modulation' started by N6YW, May 31, 2016.

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  1. N6YW

    N6YW Ham Member Volunteer Moderator QRZ Page

    Here you go folks.
    Grab a beer, some popcorn and settle back for some fine reading by a dear friend who has forgotten more
    than I'll ever know about radio. Dennis has decades of experience as a top notch broadcast engineer and
    has likely done just about anything in the field that you can imagine and probably some you would never
    expect. This sticky is for his postings only, so if you have comments please message him directly. w7tfo.jpg acdc.JPG
    W8KHK, N8ZL, AE7BT and 3 others like this.
  2. W7TFO

    W7TFO Premium Subscriber QRZ Page

    With my apologies to H.S. Thompson, I'll try and get a usable tidbit every month for youse guys that build & run AM gear.

    Stay resonated!

    KX5JT and G7SYY like this.
  3. W7TFO

    W7TFO Premium Subscriber QRZ Page


    Next time you are building a speech amp or some other audio device, here is a tip for an easy single-point chassis ground.

    A simple metal sewing bobbin can be affixed to a convenient spot under your chassis via a screw/nut/spacer.

    This in turn becomes your ground point, with a myriad of just-right holes for leads to solder in.

    Metal bobbins are plated with a solder-welcome finish, so the job goes easily.

    Shown is one I used in a regen RX I built.

    73DG bobbins 006.JPG bobbins 005.JPG

    N0EKO, N0TZU, N2EY and 8 others like this.
  4. W7TFO

    W7TFO Premium Subscriber QRZ Page

    It's about time I got a second hint posted;

    A retro high-voltage connector!

    Tired of trying to chase down any of those Millen jobs, even some in good shape?

    Get a bit of 9/16" and 3/8" brass rod and proceed.

    Slice off a piece of either some 3/8" to 1/2" long, and drill through and tap to 10-32tpi.

    Assemble as shown, using a piece of brass 10-32 all-thread. Don't run up the internal nut in the flanged porcelain too tight, it might spilt.

    Use a regular porcelain plate cap and you have it, buzzardly and pretty rugged as well.


    73DG View attachment 328822 View attachment 328821 View attachment 328820 View attachment 328821 View attachment 328822 Dreadnought 001.JPG Dreadnought 002.JPG Dreadnought 003.JPG Stack 1 001.JPG
    AA5BK, N0EKO, N2EY and 3 others like this.
  5. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Here is a tip for anyone needing a good 3/4" plate cap, other than the 'fuse clip' type.

    The brass gizmos are used to make a smaller fuse fit into a larger socket (one on each end).

    They are available at electrical supply houses for cheap. Much better than someone I know that ruined two $100 sockets to get caps for his HF-300's...

    They will fit glass tubes like the HF-200/300, WL460/468, and all the bigguns' like the 4CX5,000 and up.

    Just drill a small hole and solder in your wire..voila!

    Solar 004.JPG Solar 005.JPG Solar 006.JPG
    AA5BK, N2EY and N6YW like this.
  6. W7TFO

    W7TFO Premium Subscriber QRZ Page

    I've come up with a great source of HV oil caps for power supplies.

    Modern elevator systems!

    As shown, that is a pretty small can for almost 100uF @ 1100VDC. (according to an Aerovox tech)

    Apparently they are from large VF motor drives, and get changed out on an hourmeter for safety reasons.

    They have real porcelain insulators as well.

    I have found these on both eBay and an industrial surplus outfit.


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    AA5BK, N0TZU, N2EY and 6 others like this.
  7. W7TFO

    W7TFO Premium Subscriber QRZ Page

    An easy, cheap (if you have a dual-trace scope) way to measure THD:

    Generate a sine wave @ 1kHz, and feed it into you audio device and trace 1.

    Connect device output to trace 2.

    Adjust scope amplitudes so the two traces overlap as close as possible.

    Swing the audio generator up & down to cover the required range for the device under test.

    Any deviation from trace 1 shown in trace 2 is harmonic distortion, response limitations, or phase shift.

    Tweak device for best results.

    N0TZU, KL7AJ, AE1N and 1 other person like this.
  8. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Good-sized roller inductors. On the 'Holy Grail' list for lots of builders.

    Here is a blurb about some 4" diameter ones that were mistreated in a broadcast transmitter. They were frozen in place, due to someone putting automotive moly wheel bearing grease all over them and letting the dust settle, causing mud. This also reacted with the silver plating with some loss.

    They were lucky there were no serious burned spots, these were in a low-current node.

    I removed them, and disassembled same. A thorough scrubbing with industrial degreaser, and a long soak in Tarnex brought them back to usability.

    Just the lightest application of synthetic grease on the roller shaft and center bar and they are back at work.


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    W1BR, N0TZU, KC7ES and 2 others like this.
  9. W7TFO

    W7TFO Premium Subscriber QRZ Page

    BTW, don'tcha just love the other crappy coil forms in the rest of this masterpiece of RF tech?

    One has to be very careful not to bump into one of those Styrene beauties...

  10. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Here are some more parts from this really sad Broadcast Electronics AM-5, a 5kW PWM rig.

    Shown are three of the 5kW DC + PWM power supply units, it uses 4 of them for running 16 mosfet RF amplifier modules at better than 120% + modulation when required.

    When singing well, it will pull better than 90 Amps @ 240V 1ph off the line. Not bad efficiency.

    The closeup is one of the heavy, square-wound chokes than needed new steel banding mounts..the old ones snapped and let the thing droop and short out.

    Every electrolytic in the PSU's (over 100) were changed out...most were the originals from '95.

    73DG July 001.JPG July 004.JPG
    N6YW and AF6LJ like this.

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