[Amps] Reverse grid current on standby

[mschwab at aon.at (Michael Schwab)]

I would ask for possible input on a (to me) puzzling issue:
I am using a gg 3cx1500 amplifier. On stand-by I see a very low amount of 
reverse grid current (5-10mA) indicated. When I key up the amp and transmit it 
swings into the positive.

Metering circuit consists of a 10 Ohm resistor between B- and ground and a 5k 
variable resistor to the + side of the meter, the other leg of the meter 
grounded.

What am I missing?

Mike, OE6MBG