[AMRadio] Viking II no output


Geoff/W5OMR ars.w5omr at gmail.com
Fri Feb 9 22:02:41 EST 2007


>   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'.
>
>   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...

If the plate choke itself was open, then there wouldn't be 600'ish volts 
on the plate caps of the 6146's.

ante up.

Let me make this perfectly clear...

There -is- full plate voltage on the plates of the 6146's.  I've been 
saying 'around' 600 and 600'ish... I've not been specific because my 
RAdio Shace DMM doesn't measure more than 600vDC.  It tries to read, 
goes up - I see a two sets, quite possibly a few sets of numbers, as the 
voltage is rising, before the reading on the LCD screen read "OF" (out 
of range).  B+, as measure on the plate caps of the 6146's is 600VDC+

At No time does the plate current rise about 20mA.  Moving the Roller 
inductor around -does- dip the plate.  it dips to around 10mA and power 
output is around'ish 10w, thereabouts. (between 7 and 12)

Measuring at the tube base, there are:
280v of Screen
-57V of bias

I can draw as high as 15mA of grid current.  There just isn't any plate 
current showing on the meter, and there's not enough output to show on 
the grid input meter of my 250TH final.  I use the Viking II as the RF 
exciter (RF only) to drive the 250TH homebrewed final.  On a cue from 
John/WA5BXO, for the push-pull 250TH rig, I run around 125mA of grid 
current.  Each tube, in class C, only requires around 45mA.  A pair of 
'em need 90mA.  The Viking II will produce -much- more power than 
needed, but -this- particular rig has such a small output, that it's 
nearly not registering on the grid meter of the final.  -maybe- 10mA.  
Virtually no output.

>   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...

I only use a Viking II as an exciter for the homebrew rig.

Someone else said that typically, those capacitors would short out, 
instead of opening up.  Makes sense.  But I think it's somewhere else.

the rig is on the bench, up on it's side, with and xtals stuck in it.  
It's common everywere.

FM

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