[ARC5] GF-12/RU-17 two-pin connectors and Test Meter

[Mike Morrow]

Andy wrote:

> Speaking of the Test Meter, how was it used in practice?

It's a 35 mA dc meter.  CW-22266.

It can be plugged into jack 135 on the Receiver Switch (control)
Box to measure cathode current of the three RF amplifier tubes.

According to RU/GF set manuals:  

"The meter may be used to check the cathode current of the tubes
at full sensitivity.  Or, in the "AUTO" position of the Switch
Box switch the meter reading gives a rough measure of radio field
intensity, since this current (which increases with increased
sensitivity) will increase as the incoming radio signal becomes
weaker and decrease as the radio signal becomes stronger.  Thus
when receiving on a loop the test meater will give a visual
indication of bearings by indicating a current maximum when the
loop is set in its position of minimum received signal."

Later in the manual, this is found:

"NOTE:  For satisfactory direction finding or homing operations on
any loop the signal should be received in the CW position of the
switch regardless of whether the transmission is modulated or not.
If the Test Meter is used as a visual indicator of direction finding
or homing the Switch Box switch 134 must be on "AUTO," since the
current indicated by this meter is varied by the amplitude of the
incoming carrier only in virtue of the action of the A.G.C. tube."

The above suggest that in the pre-ZB homing system era, when a RU
set might find itself connected to a DU or DW loop instead of the
ZB homing adapter, the test meter may have found utility as a
permanently installed device at the Receiver Switch Box.

The test meter can also be plugged in to the GF-* transmitter at
jack 128 for a direct indication of modulator current, or plugged
in to jack 129 for indication of MOPA total HV current (after 
multiplying the indication by 5).  The transmitter tuning
instructions do not utilize the test meter.

BTW, the grid modulator tube (type 89) in the GF-* is always
energized and operating, even when the transmitter is not on the
air.  It functions as a two-station interphone amplifier between
the Transmitter Control Box and Receiver Switch Box at one station
and the Extension Control Box at the other.

There is actually a lot to admire technically about the RU/GF
systems of 1935 and later vintage.  They are rather clever and,
yes, advanced for the era.

Someday as one of my last projects, I'd like to put together a
complete RU-17/GF-12 with ZB-3 command set/homing system.

Mike / KK5F