got a 939 for repair. it is modified for "TX audio direct injection"
on the back of the radio, and had a "golden screwdriver" turning
this and that. 
It worked but ran so hot I was told they had to
put a fan in place of the speaker to keep it cool. 
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so yes, the "520's" bias was very high. (as usually is the case!)
I started over with my screwdrivers.
first, set it up, AM mode. turn mic gain all the way off (ccw).
use a screwdriver to short out TP3 to the nearby ground.
.
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.
this kills the RF going to the mixer.
key up with a current meter inline and turn the bias pots (VR10/12) for
minimum current. measure the voltage at TP7/8/9 and turn the RF POWER
control all the way high cw and adjust VR14 for 6.2 V. then turn all the way low
ccw and adjust VR18 for 3 V. (this worked for me)
then put back to high power full cw 6.2 V at TP7/8/9.
and while keyed up watch the input current, and adjust
VR10 and VR12 for an increase of 50 mA for each "520"
I had about .75 A total into radio.
then take screwdriver short off of TP3, key up, and adjust cans
L44 L43 L42 L40 for maximum RF output.
I got about 6.5 watts output and "520" gate voltages of 3.1 and 3.6
turned RF POWER control for about 5 watts, turned mic gain up,
and radio works great.
no need for that ass-hat fan on a 5 watt radio!
