Borgi's (K9YQQ)new rig!

Discussion in 'Amplitude Modulation - AM Fans' started by N2DTS, Feb 13, 2018.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    Pair of 304tl's behind glass modulating an 833 (the 3rd 304tl was a dud).
    Big old school goodness!
    He sure knows how to build a nice transmitter!
    Sounded great on 3880 tonight.
  2. K5UJ

    K5UJ Ham Member QRZ Page

    I've heard that rig on the air and it sounds great. I don't know if he built it for someone or if this one is for himself. He ought to treat himself to one of his rigs once in a while. I wish I could see some photos because I'd like to know more about it and a photo can tell a lot. Guys like Borgi and Bill Decker somehow seem to have an inexhaustible supply of material like racks, panels and chassis, plus sockets, meters and other hardware. Another thing Borgi is good at is getting around the lack of audio interstage iron. The 304TLs are driven by a pair of 2E26s p.p. with the 304TLs voltage driven in class A and everything RC coupled but I don't know exactly how. When he's explained it on the air I couldn't copy him well. I am assuming the grids of the 2E26s are driven by something like a 6J5 in a phase splitting configuration. No idea what the driver for the 833A is.
  3. AC0OB

    AC0OB Subscriber QRZ Page

    Borgi has built transmitters for KC9QJE (See Mr. Lincoln), W0XV, and a host of other operators.

    Borgi and a group are on 7.290, 95 around noon CST each day.

    Another custom builder is Robert, W0VMC. (Voice Modulated Carrier).

  4. N2DTS

    N2DTS Ham Member QRZ Page

    Its his, pictures on his qrz page.
  5. K9YQQ

    K9YQQ Ham Member QRZ Page

    I'll try to be brief. I have four homebrew AM transmitters in the shack. One stands alone with a built in DDS VFO and a solid state driver thanks to Jerry, W9PB. The final is a 4-400. The audio chain is a Behringer Ultra-Voice driving a Crown D-75 amp. This drives a pair of triode connected 813s in class B. The other three transmitters share an IC-718 RF exciter and a common audio chain which consists of a Senheiser MD421U mic driving a Behringer preamp that feeds a BW Broadcast DSPXminiAM processor. This feeds an audio DA that has individually adjustable outputs that feed the modulators of the remaining three rigs at +4 dbm.
    The transmitter mentioned above has an 833A in the final. The grid tank is a National MB150 modified to do 160 meters and gets drive from the IC-718. The output is a pi-net. The modulator consists of a pair of 2E26s in class A push pull driving a pair of 304TLs in class AB1 push pull. The input to the modulator is a split secondary audio transformer that drives the 2E26s. The input level is +4 dbm. The plates of the 2E26s have 50K load resistors and are capacitance coupled to the grids of the 304TLs. The plate supply for the 2E26s is 650 volts. The bias is set so that the tubes run at about 450 volts. The audio voltage needed to drive the 304TLs is about 300 volts pp. This is very close to all the 2E26s will do. I can achieve 100% modulation with about 10% headroom. The modulation transformer is a 500 watt RCA with no mod reactor. If I find a good reactor, I will put it in, there is plenty of room. I might experiment with a 1:3 interstage transformer such as the Hammond 124E between the 2E26s and the 304TLs to allow me to throttle back on the 2E26s and give me much more headroom. I hope this all made sense. Borgi
    WA3VJB, K5UJ and W2VW like this.
  6. K9YQQ

    K9YQQ Ham Member QRZ Page

    BTW, thank you for all the kind words. Borgi
    WA3VJB likes this.
  7. WZ8J

    WZ8J Ham Member QRZ Page

    Great QSO last night with Borgi, Don W9BHI, TimTron Mobile, K0SF, KC2FXE, and N9GTO joined in later with his Borgi-built rig.
    Nice to hang in there with the tall trees with my lowly Valiant.
    Forgot to add KD1NA!
    Last edited: Feb 17, 2018
    WA3VJB likes this.
  8. WA3VJB

    WA3VJB Ham Member QRZ Page

    Borgi nice working you on 40m Saturday afternoon.

    Your pr. of 4-250s into a pr. 813s is yet another of your good-sounding QRO xmtrs. Love that MD-421, and the story behind it is part of the charm.

    Enjoyed listening to you on the Motorola R390. I also was running a '421 into this little RCA mixer.

    Attached Files:

  9. KM1H

    KM1H Ham Member QRZ Page

    Wouldnt 6146's help with the headroom or 6550's, some KT variants, etc? While the 2E26 is a very underutilized tube and dirt cheap there are alternatives to adding iron.

  10. WA3VJB

    WA3VJB Ham Member QRZ Page

    Must be nice: Borgi said he has dedicated three of his homebrew transmitters, one each to 160, 40 and 75 meters.

    "Don't have to set everything."

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