Show off time! Post some photos of your AM-centric shacks!

Discussion in 'Amplitude Modulation' started by N6YW, Jul 17, 2019.

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  1. W8KHK

    W8KHK Ham Member QRZ Page

    Brett, thanks for the kind words. Yes, my grandfather was very serious about attention to detail. He liked things balanced and symmetrical, maybe attributable to his other passions: Astronomy, Building reflecting telescopes, and boat building with sheet steel, typical were 36 foot or so cruisers and sailboats. He taught me to solder when I was four, and then at eight he taught me oxy-acetylene and electric arc welding. I spent a great deal of time on the restoration, no small amount was invested in locating and repairing vintage matching meters.

    Unfortunately, some of that 250-TH rig did not make the trip from NJ to FL when dad retired. We no longer have much of the original power supply, or the exciter/driver deck using the 35-T and 100-TH that was mounted directly below the final deck as seen in the earlier photos. You can see in the recent restoration that the modulator was moved up directly below the final. It used to have metering for the final grid and plate current, plate voltage, and plate current for each of the 810 modulator tubes. There was no overload protection, and no fuses or circuit breakers anywhere in the rig. The final used just grid leak bias, and the modulator a dry battery under the chassis.

    When I restored it, I added regulated bias supplies, with grid voltage adjustable for each individual modulator tube. Over-current trip relays with indicators were added as well. Adjustable filament voltage with metering was added for mod and final tubes. Variac for plate voltage, and separate rectifier and filter circuits for mod and final. I restored the mod and final decks pretty much as they were originally. Circuit breakers and fuses were added where appropriate.

    The mod deck has an input transformer with 500 ohm primary, and uses the high-end "CHT" (Chester H Thordarson) iron, very pretty units. A separate speech amplifier was used, and I restored a 1955 version of the UTC MLF (multiple loop feedback) amplifier for this function. The engineers at UTC spent the better part of a year analyzing the Williamson, and several other designs, and determined that large amounts of global feedback actually caused problems such as ringing, overshoot, instability, etc. These problems were apparent when using a step-function input signal, but they were obscured when using a typical continuous sine wave input for testing. They arrived at a combination of a small amount of global feedback, and three local feedback circuits throughout the amplifier. This resulted in superb stability, low distortion, and low output impedance which turns out to be ideal for driving triodes into grid current. This is quite an amazing feat for 5881s (5L6s). There were at least two articles available in periodicals describing the work, and I can make them available if you are interested. I noticed in another thread that you were using local feedback, but you were not a strong proponent of large amounts of global feedback.
  2. W8KHK

    W8KHK Ham Member QRZ Page

    John, as I mentioned to Brett in a previous post, this rig is all hollow-state, with a 1950's UTC performing speech amplifier duties. I had originally intended to use the sand-state mosfet driver with my PP 304-TL rig, which has 304-TLs as modulators. But Frank mentioned that the mosfet driver likely has insufficient swing to properly drive these tubes. So I am reserving that board for a pair of 833 modulators. My brother, and another friend, who received one of your boards, will each be using the board for 813 modulators, as you are. I already have most of the required components.

    When you ask about boards, I assume you are referring to the audio processor project. We are currently on the third revision, and we have defined some very important additions and improvements, so I am now working on the artwork updates for the fourth revision. The second and third were created in December and February, so we are due go to fab on the final board very soon. We will have several early-adopters running the earlier board with mods doing on-the-air evaluations. Yes, we expect to have boards and lots of the components "left over", as it is not practical to fab just one or two. If you are interested, keep in touch. We will use other avenues to share information about the project, and will only discuss the technical aspects here. You are welcome to participate in the testing of the earlier revision device if you are so inclined.
    Last edited: Jul 21, 2019
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  3. N2DTS

    N2DTS Ham Member QRZ Page

    Its great you carry on the high standards of the family!
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  4. W8KHK

    W8KHK Ham Member QRZ Page

    Maybe not truly AM centric, but I was wishing I was on AM in my barracks at Davis Monthan AFB, Tucson Arizona in 1967. My new call was WB2HKX from New Jersey, and I also had AFC2HKX Mars call. I had not yet built the 4-400 amplifier, but I did have inverted vees on the roof of a 3-story barracks, and the center support was a 40 foot push-up pole with a CDR rotator spinning a borrowed three-element 15 meter Gotham beam borrowed from Gary Cormack, WA7GFT. He also loaned me the SB-200 until my home brew amplifier was completed. A gentleman and a scholar. I worked all states from this location in less than a year.
    I used a Heath SB-101, SB-200, and HRO 5. I wished I had that 250TH or 304TL, but no way in a barracks room with three other people.

    The sleeping quarters in the corner were dwarfed by the station equipment, but we did save room for the refrigerator and microwave.

    img00018.jpg img00019.jpg
    N6YW likes this.
  5. VE3PP

    VE3PP XML Subscriber QRZ Page

    IMG_3548.JPG IMG_3551.JPG It's humble, it's not a heavy duty boat anchor station but it does operate AM.
    WA8OLN likes this.
  6. WO4K

    WO4K XML Subscriber QRZ Page

    W7KNX, W0AQ, KW6LA and 5 others like this.
  7. W8KHK

    W8KHK Ham Member QRZ Page

    Very nice, organized, functional layout. Custom shelves put the heavy metal where it is convenient to operate. Knotty pine has a special warmth to it. Mic collection tops it off! Kudos!
    WO4K likes this.
  8. KE0ZU

    KE0ZU Ham Member QRZ Page

    Definitely promoting "Authorized Modulation", but certainly not nearly as impressive as many of the previous heavy metal posts.

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
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  9. K4CCW

    K4CCW Ham Member QRZ Page

    Always amazing and inspiring to see your collection, Mike.

    As I looked at these views this morning I was made to wonder, “How much longer is he going to be able to rotate these beauties through the op desk for their exercise?”

    I know every time I even think about it, my shoulders begin to provide “negative feedback”.
  10. WO4K

    WO4K XML Subscriber QRZ Page

    I like the D-104 on a boom! I did something similar in a previous shack...

    Mic installed.jpg
    W7KNX, W0AQ and W1TRY like this.

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