Ranger 2 - Loss of grid drive

[WA3MJY]

I am having problems with intermittent loss of grid drive in my Ranger 2 transmitter. I noticed the smell of a burnt resistor but could not find anything when looking at the underside of the chassis. Does anyone have any suggestions?

[wa3dsp]

It could be the front panel drive pot. It is fully across the LV B+.  It is a 4W pot and with a 300V low B+ it is already at 3.6 watts. With higher line voltage and higher B+ its rating is often exceeded.  I dealt with this in my Ranger upgrade - http://www.crompton.com/hamradio/JohnsonRanger/RangerRestoration.html  - my pot was opened and I replaced it with a smaller pot and a mosfet.

Do you have good osc. and buffer meter readings or just bad PA grid readings?

[wa3dsp]

Another question I would have is this just happening in the CW or AM positions or do you see the PA grid current jumping around in the tune position also?

If you are not seeing it in the tune position then it could be the clamp tube. The grid of the final and the grid of the clamp tube are DC connected. You can check the clamp tube operation by turning the drive all the way down. In the CW position key down you should see no more than about 40ma of plate current. If it is appreciably more the clamp tube is not working. The current you do see when the clamp tube is working is not PA plate current but rather the current through the PA screen resistor to ground through the clamp tube.. The clamp tube fully cuts off the 6146 by grounding its screen.

Also if you are smelling a good aroma of resistor and you can not see anything it could be in the VFO. Especially if the osc and buffer readings are jumping around. There was an article about that in ER - "The dreaded Johnson Ranger VFO disaster"  Feb - 2001. Lets hope that's not the case.