[AMRadio] Viking II no output


John Lawson jpl15 at panix.com
Fri Feb 9 22:51:31 EST 2007



On Fri, 9 Feb 2007, Geoff/W5OMR wrote:

>
> ante up.


  Not till you finish trouble-shooting!



>
> 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'm not sure trhere should be that much - if the tubes are conducting.



> 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).


   Ummm - eBay - better meter? To maintain your BA stuff? Decent test gear 
is a must - and cheap if you scrounge the swapmeets, eBay, etc.  Even a 
1KVDC panel meter with well-insulated test leads...  c'mon.



   B+, as measure on 
> the plate caps of the 6146's is 600VDC+
>

   Sounds like too much at the caps. Perhaps I'm wrong - the Valiant is 
roughly the same circuit, but with three of 'em. Under load it's different 
- but you must use a meter that decouples the RF, if the stage os working, 
or it 'swamps' the typical el-cheapo DMM...



> 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)
>

   I got this already.


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

   Dude: What Is The Voltage On The CATHODES????



> I can draw as high as 15mA of grid current.  There just isn't any plate 
>

   I got this the first couple of times you wrote it.


   But you still haven't checked the voltage at each step in the Final Amp 
B+ chain - from the place in the circuit that B+ comes in (The 'bottom' of 
the Plate Choke) to the place where it meets ground - somewhere right 
after the cathodes of the 6146s.


   If you find that there is a complete path to ground for the usual DC 
PLate current - THEN you can be reasonably assured that the tubes are 
operating properly - and that the trouble is elsewhere.  And yes, those 
old Johnson doorknobs do fail - I replaced all of them in my Valiant and 
both Rangers - one had split in half, yet the rig still loaded up and 
'talked'...  the fact that the tubes will only pass 10-20 mA, yet they are 
under proper bias - is very suspicious and 'telling'..


   That's why I tried to offer a logical 'checklist' - to trace out the DC 
Plate Current path *completely*.  I still would like to know what the 
voltage is on the 6146s from pins 1, 4, and/or 6 w/respect to ground. If 
they all go to the same wire, and that wire has come off it's lug - the 
symptoms you describe will most likely be evident.

  But at least you will have logically eliminated a bunch of Things that 
could be causing your trouble - and it will only take a few minutes to 
check the various places with your DMM...

   Also - please be careful - especially with cheap meter leads and HV...



Cheers

John
KB6SCO




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