[AMRadio] Viking II no output


John Lawson jpl15 at panix.com
Fri Feb 9 20:06:05 EST 2007



   Hmmm - so many helpful/hopeful answers.

   Geoff - all of us being Hams, and hopefully Licensed Hams - and in our 
'end' of the Hobby - hopefully we're somewhat removed from the realm of 
the 3-day blitz-license appliance-operator type ...   I'm wondering if the 
usual flow of logical, point-to-point troubleshooting steps have been 
undertaken here? There's a lot of "shotgunning in the dark" going on...


   Given your very clear description of the symptoms - obviously the finals 
are not drawing anywhere enough plate current. How can this be? I'd get 
'er on the bench, tied to a dummy load, and operating in her 'failure 
mode'.

   Okay - B+ comes from the Power Supply, goes through a few components, 
through the final tubes, into the cathode circuit, thence to ground.  IIRC 
(not being a Viking II owner) that the plate current meter is also in the 
cathodes of the finals, measured across suitable dropping resistors.

   Going in this direction with a voltmeter - what is the B+:

  1. At the B+ side of the Plate Choke?

  2. At the Plate side of the B+ Choke?

  3. Before the Plate cap coil/resistor combo?

  4. Directly on the caps of the Finals?

    If this gives the expected voltages, what is the voltage from the 
cathode pins of the finals to ground? Ie. are the cathode resistors open?

    You say 10 mA at resonance, 20 mA off-resonance - so the plate circuit 
dips properly - RF is getting into that network, just no actual power, as 
in B+ divided by the DC Plate Load of the finals to ground type power.


   I'll betcha a buck that following the B+ Plate DC circuit from start to 
finish, will quickly and easily reveal the Problem - and I'd probably be 
willing to up my ante a quarter to surmise that the Plate Choke itself is 
open...


   Hopefully this may be of assistance - and also gets you back on the air 
- so we can work an all-Johnson AM Night sometime...  that'd be Fun...


  Cheers

John
KB6SCO
DM09fg





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