[Boatanchors] National NCX-3 Final Bias Adjustment

[Mark V Johnson]

Team,

 

I have a National NCX-3 transceiver on the bench and I have a question about
the final tube bias adjustment.

 

The transceiver has good output and I've made contacts with it, but the
control grid bias voltage spec is -45 to -55 VDC. If I set the bias adjust
pot on the rear of the chassis for max, I can get the bias down to -51VDC.
On spec. However, when setting the bias pot as per manual: key mic with no
output and adjust pot for 50 to 60 ma on meter, the actual bias voltage goes
to  61VDC and my  actual RF output drops. 

 

I have several National Service Bulletins and they cover a wide range of
changes/improvements but nothing related to my problem. 

 

The rig has 6GJ5's installed.

 

Is there another service bulletin related to this? Should I adjust bias by
setting the DC voltage or by using the IC meter?

 

Many thanks. 

 

Mark V Johnson

VE3LU/VE3DJU