[Milsurplus] Need help with ART-13

[mac]

Tricky little point on ART-13 metering not clearly covered in the TM:

The meter on the front of the transmitter has both a 0 - 200 scale and  
also blocked off ranges for CW (white), Phone (red) and MCW (white).   
As originally designed the numerical range DOES NOT CORRESPOND TO THE  
ACTUAL CURRENT IN MILLAMPERES.  In operation, the set was tuned and  
loaded to put the meter needle anywhere in the CW block.  The middle  
of this block is also mid-scale on the meter or 100 on the numerical  
scale but actually corresponds to approximately 150 ma. plate  
current!  In Phone and MCW both the plate and modulator currents are  
being measured together, here, and so the meter will kick up into the  
red “Phone” area under modulation. Above something around 20K ft.  
altitude the PA plate voltage was reduced (as described by Robert) and  
so the plate current would reduce also, and to keep the meter reading  
in the right block on the scale the value of the series metering  
resistor was increased to give a mid-scale reading of about 100 ma.   
All this was done to make life easier for the operators, i.e., don’t  
worry about the numbers, just keep the needle on the right color.  To  
do all this, the dynamotor had a 20.1 ohm metering resistor tapped at  
13.4 ohms.  For ham use, however, just use a 25 ohm pot in the  
negative lead of the HV supply and adjust to make the meter read  
whatever you want.


Dennis D. W7QHO
Glendale, CA