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Need help from amp builders

Discussion in 'Amateur Radio Amplifiers' started by KN4CTD, Nov 16, 2018.

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  1. KN4CTD

    KN4CTD Ham Member QRZ Page

    Also, I think I will “remote” the bias adjustment pot to the back of the amplifier to make it easier and maybe safer in the process
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    When I used Tony's bias board, I mounted it under the perforated cover in my Heath SB-220 on a scrap of angle stock:
    This allowed easy access (with the outer cover removed). :)
    KN4CTD likes this.
  3. KN4CTD

    KN4CTD Ham Member QRZ Page

    I tried my best to find a suitable location for the board inside that’s easy to access, but unfortunately, the way the filter cap/power supply board mounts, I’m limited. Tried to post a pic, but the “file is too large”
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You can re-size the image and try again.

    I've never tried building much of anything without drawing a schematic diagram first, so I can "de-bug" the schematic over a few hours or days and then start building.

    To homebrew something as complex as an amplifier without a schematic is almost amazing.
    WQ4G and WA7PRC like this.
  5. WA7PRC

    WA7PRC Ham Member QRZ Page

    I see lots of yuuge images. Each pixel's info adds to the file size. I use a graphic editor to crop/rotate/resize/etc images. Then, I upload to my image host, Flickr. When that happens, Flickr automagically creates smaller versions, down to 75x75 pixels. I can then use whatever size I want on ANY online forum using the "IMG" tags like this:

    If I use a smaller "thumbnail" image, using the URL tags, I can link to the larger image by "nesting" the thumbnail image like this:
    (click for yuuge image)
  6. KN4CTD

    KN4CTD Ham Member QRZ Page

  7. KN4CTD

    KN4CTD Ham Member QRZ Page

    This is a terrible schematic. I'll have to re-draw it all nicer and more complete. I just wanted to basically show how all the tube wiring and bias switching was done. I took no pains to lay out the tuned input board, bandswitch correctly as I've already checked the output tank on all bands using the Mfj analyzer and I'm sure I'll have to tweak and play around with the tuned input some more. It uses the multitech industries bandswitch designed for the kenwood tl-922 amplifier. It was a perfect fit and simplified the band switching setup over what was originally in the chassis (which was severely arced junk). Padding caps are switched in for 80 and 160. I can draw a schematic of the control circuitry and hv supply board if need be. This is my first attempt at any of this, so let me know what I need/should do differently. Especially anything that may appear to be dangerous in any way. The first time hv was applied and keyed with no rf, no amount of adjustment on the bias board pot changed the idle current of the tubes. I will add one more tidbit of information that I forgot about but am embarassed to admit to also. When I first got these tubes, I applied 120vac to the secondary of the filament transformer for a split second (loud hum) while the tubes were in the sockets and connected to the primary......I fixed my mistake immediately but with no other way to test the tubes at the moment I'm unsure. Did I kill them? The filaments still heat up and they show no shorts with checked with an ohm meter. I also ohmed out the transformer and it seems fine. In any event, I have a new set of tubes on the way in case I need them. Thoughts?

    Attached Files:

  8. KN4CTD

    KN4CTD Ham Member QRZ Page

  9. KN4CTD

    KN4CTD Ham Member QRZ Page

    Does the 100k cutoff resistor need to be moved from its current location ,according to the schematic , and placed directly in series with the B- before being connected to the common pole of the relay?
  10. KN4CTD

    KN4CTD Ham Member QRZ Page

    A couple of corrections regarding the schematic I threw together ......the safety choke goes to ground and is wired as such, I just messed up drawing it and there are no bypass caps on the tube side of the filament choke. They are on the filament side.....also drawn wrong

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