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Swan 500 - S Meter moves with Audio Gain Control

Discussion in '"Boat Anchor" & Classic Equipment' started by VK6UG, Feb 23, 2017.

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  1. VK6UG

    VK6UG Ham Member QRZ Page

    I have a Swan 500 and spent quite a bit of time restoring it. It is now working well on receive and transmit.
    One thing that has me puzzled though:
    when you back off the audio control with the RF gain sitting at around say 12 or 3 o'clock the S Meter moves to the right and if you reduce the audio down far enough the S Meter is at the end of the scale. I have replaced the electrolytics and the diodes in the RF gain circuit and all the valves have been replaced. I can see that the audio pre-amp, the 12AX7 V10 is related to the other 1/2 of the 12AX7 in the product detector, which is related to the second IF v9 where the S-meter circuit is found. As to how the Audio Control is controlling the S-Meter I do not understand.

    Any help or advice would be appreciated.

    Thanks,
    Milton VK6UG.
     
  2. G3YRO

    G3YRO Ham Member QRZ Page

    That is what usually happens on most Valve rigs when you back off the RF Gain . . .(but obviously NOT the AF Gain)

    What happens to the S Meter when you back off the RF Gain?

    I see they are concentric controls . . . are you sure the two knobs aren't sticking together, so that when you are turning the AF Gain down, you are also moving the RF Gain?

    Roger G3YRO
     
    KE4OH likes this.
  3. KE6RWB

    KE6RWB Ham Member QRZ Page

    Milton,
    The Swan 500 has the RF Gain and the AF gain knobs all on the same location. Its a duel function knob meaning the outer ring moves one function and the inner ring moves the other function. Ok so here is the deal on a 500. They connected the functions up backwards to all other swan radios on this model. The Black outer know changes the RF gain and the inner silver ring controls the AF gain. I dont know why but my son has one and every time I operate his rig it drives me nuts. I told him to unsolder the wires and move them.LOL

    Terry KE6RWB
     
  4. KL7AJ

    KL7AJ Ham Member QRZ Page

    Are you sure you haven't swapped the wiper and one of the outside terminals of the pot? Sounds like the pot is shorting out the previous stage in the full "down" position.
     
  5. KE6RWB

    KE6RWB Ham Member QRZ Page

    I had a typo in my last message.The Black outer knob changes the RF Gain. Milton look at the stencil writing on the face of the radio. It is reversed from other Swan radios or for that matter any Boat acnhor I have operated. I asked my son did you change that and he said no John Bruchey told him thats the way they come from the factory. Go Figure.
    Terry KE6RWB
     
  6. VK6UG

    VK6UG Ham Member QRZ Page

    Hi, thanks for all the replies. It turns out that the control functions in my Swan 500 are 'reversed' i.e., the knob (front) is the RF gain and the slider (rear) is the Audio. I have another Swan 500 and these controls are the other way around. It has been pointed out to me that some Swan 500s were built deliberately like this. I can see some logic in the choice of slider rear as audio, but would think the reverse is better. I will leave it as built!
    Confusion solved.

    Regards, Milton.
     

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