[Amps] AL-1200 Grid Current - negative?

[Dana Roode]

Continuing this thread...

In addition to the bad resister inside the meter, the two 1.5 ohm grid 
resistors were open (thanks to W1QJ for encouraging me to check those too).

Several weeks back I posted my AL-1200 story - I was using it on 40meters 
during a contest when it arced.  The IC756ProII connected to it went south - 
  the transmitter no longer put out any RF.  ICOM has it, they say some 
protective diodes were taken out.

Earlier, I discovered that the resistor in the parasitic suppresser came 
unsoldered.  Is it a reasonable theory that the parasitic suppresser failed 
causing some self-oscillation and excessive grid current that took out the 
grid resistors (and my 756proII)?  Or should I be looking for a different 
underlaying cause?

I'll be picking up some new grid resistors and taking it from there.

   Dana



Dana Roode wrote:
> Amps folks -
> 
> Ok, I removed the tube and the meter still went negative.  I checked the 
> filament connections with the tube out, nothing is shorted to ground.
> 
> I was suspect of the metering circuit itself.  The left multi-function 
> meter measured 300 ohms across the terminals, the right grid meter 
> measured 15k. The parts list indicates both meters are 300 ohm 1ma.
> 
> I took the grid meter apart, it has a component (a precision resister, I 
> assume) in series with each internal meter movement lead.  One measured 
> 100 ohms, the other about 15k.
> 
> I am pretty clueless about this, and Im at a loss as to why a 100ohm 
> resister would become 15k, but perhaps this is my problem.
> 
>   Dana
> 
> 
> Dana Roode wrote:
> 
>> What does it mean when you power up an AL-1200 and the grid current 
>> meter pins negative (no drive power supplied)?
>>
>>   Dana
>>
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