V2 and 122 vfo

Discussion in 'Amplitude Modulation - AM Fans' started by N8ZL, Jan 12, 2019.

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  1. N8ZL

    N8ZL Ham Member QRZ Page

    When using the 122 vfo with my V2 on 20 meters I generate 2 signals about 200kc apart. The unwanted signal is weak but still can be heard. It works fine with xtals and is clean on other bands including 10 meters. Wonder if anyone else has expirenced this?
     
  2. K5UJ

    K5UJ Ham Member QRZ Page

    I have a 122 with an HT-20 and as far as I know it is fine, but I've never run mine above 40 m.
     
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    http://amfone.net/Amforum/index.php?topic=24574.0

    This discussion at the AM Forum, doesn't address your specific matter, but discusses a number of general issues that may relate. b.

    Your post is quite terse. More info would be helpful.
    -My assumptions: You are referring to a Viking II and VF-122 VFO

    -How are you hearing this second signal?
    -Is it higher or lower in frequency?
    -Have you done any sniffing with an Oscope or Spectrum Analyzer?
    -Have you tried using a separate power supply for the VF-122? This is a common cure for VF-122 problems.
    -Have you replaced any components in the VF-122?
     
    Last edited: Jan 12, 2019
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Last edited: Jan 12, 2019
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    QAA:

    The truth be known, the VFO is not a VF-122! The official E. F. Johnson Company nomenclature is Viking VFO model 240-122.

    The Heath VF-1 is, basically, a "knock off" of the 240-122. That VFO is definitely MUCH happier with a separate, regulated, power supply. Also, both VFOs work much better if the 6AU6 is replaced with a 6AH6 and the 0A2 screen voltage regulator replaced with an 0B2. This reduces the screen voltage from 150 VDC to 108 VDC. A regulated 150 VDC needs to be applied to the VFOs instead of the original 250 VDC to 300 VDC. You can use the 0A2 removed from the VFO to regulate an external power supply.

    Exchanging the tubes has no real effect on either model VFO. However, the frequency stability is considerably better with the new tube types.

    Glen, K9STH
     
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  6. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    EF Johnson Viking II photo (try again).

    Kit in 1952: What cost $279.50
    would cost $2,624.30 in 2017.

    [​IMG]
     
    Last edited: Jan 12, 2019
    N2EY likes this.
  7. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    upload_2019-1-12_15-38-16.png
     

    Attached Files:

  8. K4KYV

    K4KYV Subscriber QRZ Page

    Wonder how that would work in the 75A-4, to change the 6BA6 to a 6AH6.

    Years ago I improved the stability of my VF-1 by re-locating the oscillator coils to the same side of the sheet metal enclosure as the tunable slugs, as in the DX-100 VFO. With coil mounted on one wall of the box and slug on the other, temperature variations cause expansion and contraction of the whole box, moving the slugs slightly relative to the coils.

    I did it by drilling two holes in the side of the box on either side of each slug, and turning the coils around so the ceramic coil forms are attached to the same piece of sheet metal right at the some point as the slugs. Best to temporarily remove the slugs before attempting to drill holes.
     
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  9. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    KYV:

    Which circuit?

    The 6AH6 has about 3-times the transconductance of the 6BA6 and the input / output capacitances are quite a bit different as well.

    Glen, K9STH
     
  10. K4KYV

    K4KYV Subscriber QRZ Page

    The oscillator stage in the PTO, which is a 6BA6 in the A-4 instead of the 6AU6 in the VF-1. The transconductances and capacitances of the 6BA6 and 6AU6 aren't that much different. The main difference per the tube charts is that the BA6 is remote cutoff and the AU6 is sharp cutoff; not sure how much that difference affects performance as an oscillator, although oscillator tubes are usually remote cutoff. The AH6 is remote cutoff, has higher transconductance, higher filament current and the internal capacitances are a little higher. If the AH6 yields better stability in the VF-1, shouldn't it do likewise in the 75A-4 PTO?

    http://electronbin.com/sheets/127/6/6BA6.pdf
    http://electronbin.com/sheets/127/6/6AU6.pdf
    http://electronbin.com/sheets/127/6/6AH6.pdf
     

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