Discussion in 'Amplitude Modulation' started by W2NBC, Jan 16, 2020.

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  1. W2NBC

    W2NBC Ham Member QRZ Page

    Well, repurposing might not be totally accurate..

    However, using a worn-out forlorn chassis, and actually utilizing it, might be a better description..

    Parts source: Rusted-out Heathkit HG-10 VFO..

    Project: DDS HF VFO and interstage amplifier used to excite a myriad of transmitters in the shack.

    and da beat goes on..

    Any other“repurposed” gear to see here?
    Last edited: Jan 16, 2020
    KA0HCP, WA3VJB, W2VW and 2 others like this.
  2. WA3VJB

    WA3VJB Ham Member QRZ Page

    Nice looking work Jeff. The cut jewel pilot light is a vintage touch.
    And I am among those who notice you lined up all the screw heads.
  3. K5UJ

    K5UJ Ham Member QRZ Page

    I agree with Paul. You could start a business buying up and converting HG10s. As I think I have said before, I never figured out or understood the part where the solid state DDS circuit interfaces with the tube parts for higher v. output to drive 6AG7s etc. And, the BP40 is sounding GREAT on 160. I found a RE20 pop sock for it on eBay.
  4. WA3VJB

    WA3VJB Ham Member QRZ Page

    Your project got me thinking about some gear we had at W3EAX, the University of Maryland station. There was a unit about the size of an R390, actually there were two of them, one for parts, that we used for a homebrew transmitter built by N1QG, a Master's candidate in the Physics Department. Gorgeous VFO, but the name doesn't give it justice. It had INNER OVEN and and OUTER OVEN and continuous flywheel tuning oh so smooth. And here you are doing most of all that with a small tabletop box. If only you could get the glow and the aroma of hot dust on tubes and the ovens.

    Attached Files:

    W9WQA likes this.
  5. K4KYV

    K4KYV Premium Subscriber QRZ Page

    I don't think it was the same unit, but I remember running across a similar "synthesised" VFO that had two Collins PTO, several mixer stages, band-pass tuning stages and about 20 tubes. I was flying and the thing was too heavy to carry on a plane, so I parted it out and kept the PTOs and a few of the components. Unfortunately, none of those PTOs have a frequency range of any use to anything I have ever wanted to build.
  6. W2NBC

    W2NBC Ham Member QRZ Page

    Paul, that’s a beautiful looking “master oscillator” !

    The impetus for constructing a common and stable shack signal source is because of the way AM is received these days.. Not one to worry about channelized operation,(when everything has to read .00 or .50 on your dial), I DO care about having a station hear the synchronous lock wining around if the “VFO” I’m using creates havoc. It can sound like a dog in heat howling at the moon.. Those listening to software defined radio stuff, or the Sherwood REAL sync detectors can relate..

    Rob, the DDS amplitude (rf out) is variable and coupled to the buffer amplifier and can provide over 25V PP. Even with an input mismatch, it’s more than enough voltage for the “crystal” input on any commercial transmitter in the shack. That includes a Lysco 600 (with homebrew modulator), Johnson 500, Globe Champion 300, and even to the Collins 32V1 (another topic) .
    The big homebrew transmitters get yet another stable signal source: the ONLY slop-bucket capable rig in the shack, a “made in USA” Ten-Tec Omni 588 that excites the 4X1 and the “Connecticut Kilowatt” 849-modulated transmitters.

    .. And cool beans on the BP-40 OM!

    I built a receive band-pass preselector (pic below) used for the SDR receiver in the shack, and decided to build a second identical unit to really clean up any products on the DDS VFO before it gets fed to the transmitters. Works FB .

    By the way, can anyone identify the origin of the “repurposed” VFO knob on the DDS?

    Last edited: Jan 16, 2020
    KA0HCP likes this.
  7. W1NB

    W1NB XML Subscriber QRZ Page

    Looks like it’s from a KWM380. Nice looking unit. What is in your buffer/gain stage?
  8. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Its fairly easy. Here is the way I interface mine to a VFO-122.

    For higher RF voltages adjust R4 to a lower value so that the input to the counter is about 150 mV p-p.


    Attached Files:

  9. K5UJ

    K5UJ Ham Member QRZ Page

    If I had $1 for every time I've read something like that over my career, then encountered documentation that omits some key piece of information I'd have a nice IRA. I see a black box with leads, a coupling cap, a voltage divider network, but I don't see a tube or grid or anything that actually lays out the connection to a high impedance tube grid.
    That was my guess too.
    You got to have a US driver; I always razz operators when I walk into their shacks and they have a Collins/Gates/Raytheon/RCA rig with a Kenwood generating the RF for the PA.
    My SE3 usually can follow a drifting VFO but the big problem is when there are a few stations on or near a frequency and they don't bother to zero beat each other. Then I have to retune each xmission if I'm using the SE3 and if a breaking station is not zero beat to the currently transmitting station I will only hear a heterodyne and have no idea who is calling.
    N2EY and W8SMN like this.
  10. K5MIL

    K5MIL Ham Member QRZ Page

    Here is my monitor scope. It is a modified Eico 435 Scope turned on it's side.

    Bill - K5MIL

    Attached Files:

    KE5YTV and W2NBC like this.

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