Ham Nation Pine Board Project discussion

Discussion in 'Homebrew and Kit Projects' started by KD8YQC, Mar 25, 2017.

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  1. K9EID

    K9EID Ham Member QRZ Page

    HI T
    erry

    We have mentioned it several times that MFJ has the 2.5 mH chocked as well as the final coil. MFJ will sell you each and every part that use to build their equipment. Look through their catalog... It is amazing... Good luck and please stay in touch

    Bob Heil
     
  2. K4RJJ

    K4RJJ Ham Member QRZ Page

    Hello all. I'm a bit late to this party. Can I use the 12AU7A instead of the 12AX7 listed?
    I'm building a hamfest shopping list for this summer. Also can trade 3D printer work for Pine Board parts.
    Thanks!
    Ronny
    K4RJJ
    East TN
     
  3. K9EID

    K9EID Ham Member QRZ Page

    Hi Ronny

    The 12AU7 will have much lower gain and not work well at all. Best to use the good ole 12AX7.
    Stay in touch want to see your 3D printer parts..... !
    Dr. Bob Heil, K9EID
     
  4. W9BRD

    W9BRD Ham Member QRZ Page

    I say amplitude-modulating an oscillator is a bad idea because it will, not may, result in simultaneous amplitude and angle modulation, which equates to "signals that take up more bandwidth than necessary." Anyone with access to QST back issues and ARRL Handbooks from the end of WW2 up to the general absence of paid technical-editing staff at ARRL HQ will find no such implementations (at MF/HF) across that period because of that technical limitation running up against the "no simultaneous AM and FM" long codified or implied in the FCC regs. (Amplitude-modulating a Boosted Pierce transmitter--such as the classic 6C4-5763 lineup--is similarly technically unsound because of reaction on that lineup's oscillator from its final.)

    So, good thing these rigs are low power.

    Pssst, users of signal-tube-crystal oscillators who seek to banish chirp and yoop on CW, which is especially common at 40 meters with 40-meter crystals: A grid-bias resistance of 2.2 k to 15 k -- experiment; 2.2 k seems right for 6V6ish tubes, 10 k seems right for the 5763/6417, instead of the usual 47 k or higher -- will all but banish yoop while increasing output power. (Some detuning to the low-frequency side of max output completes the job.) This weekend just got a 7061 (mobile-ruggedized 12AB5, essentially a 9-pin 12AQ5, which is a 7-pin miniature 12V6) to do 5 W out, chirp/yoop free, at 40 meters with 275 V key down on its plate and only a 15-k dropping resistor--no voltage divider or VR tube necessary--from plate supply for screen feed. Long live the AC-1!

    Best regards,

    Dave
    amateur radio W9BRD
     
  5. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Hi Bob:
    Alas, I won't be able to make it to Hamvention this year; I always enjoy your talks.
    Our little group had a blast building the pineboard transmitter, and we're all impressed with how clean the audio is. In the past few months I've acquired a few vacuum tube regenerative receivers (I've always had a number of solid state ones around), and I believe these would make a great companion to the pineboard transmitters. Folks have forgotten just how sensitive the regen receiver can be...and if you're skilful, it can be used for SSB, as well.

    Here's one of the regen receivers I recenty picked up. Works great...and I think I'll modify it for 80 meters.
    73!
    Eric
     

    Attached Files:

  6. G4JQT

    G4JQT Ham Member QRZ Page

    This looks fascinating - a nice vintage project for the winter evenings. But conspicuous by their absence are any comments about the modulation quality, or photos of the modulation 'envelope' into a dummy load, modulated by a very low distortion audio sine wave. A nice trapezoidal waveform from this circuit would be particularly useful. Many of us pursue good quality AM transmissions. Will this design do that? I see no reason why not, but I see no evidence either.

    Thanks and 73,

    Ian, G4JQT
     
  7. K9EID

    K9EID Ham Member QRZ Page

    Hello Ian
    Thanks for your note and interest in the pine Board Project. Nearly a thousand have been built and more oil the way!
    No worry about the audio-…. It is scary how good it really is. Pay attention to my pre amp design with two back active equalization.
    I get marvelous reports from my original. Have to keep in mind that it all start with the microphone !

    All of the parts are available from Antique Electric Supply in Mesa, Az.

    Always here to help. Please stay in touch
    Dr. Bob Heil
     
    G4JQT likes this.
  8. G4JQT

    G4JQT Ham Member QRZ Page



    Thank you Bob for your swift reply.

    I have no doubt the audio amp sound quality will be superb, but in my experience with some home-brew AM designs the modulation quality starts to deteriorate in the high-level mod section, around the mod transformer or choke/PA anode, and to some extent with the PA loading. I expect the modulation technique was chosen with care, as a balance between performance, reproducibility and cost.

    I hadn't found anyone yet displaying some nice clean 85 - 95% modulation envelopes or trapezoidal displays for the Pine Board Project. These usually get proudly shown along side home brew AM transmitters. (Apologies if they are there somewhere but I missed them.)

    Has anyone tried detecting some audio from the RF output and using it as negative feedback to a previous audio stage? (I'm an ex-BBC engineer so am keen to see the measurements of modulation and distortion; I know - this is just a hobby but I can't help myself!)

    When run into a dummy load (probably with a short length of wire) it would make a show-piece Part 15-type transmitter for displaying and using at vintage radio shows. So I'm very keen to know what the audio quality sounds like. We don't actually have anything similar to your Part 15 regulation in the UK, but a blind eye is turned to a few hundred milliwatts on medium wave, particularly as more and more AM stations are closing and moving onto DAB, the internet, etc.

    Anyway, a big thank you to you and all those who have contributed to this fantastic project. It must have developed into a huge amount of work, especially when you reply to folks like me! I've seen some detractors saying it's a backward step, but the hobby has many rooms and this rekindles real home brew. It seems you're also drawing in youngsters who can experience the thrill that us more mature amateurs experienced by creating such apparatus many decades ago...

    Thanks again,

    73,

    Ian, G4JQT
     

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