[ARC5] Differences between RU-16 Through RU-19

[Mike Morrow]

To support what Robert wrote about the differences between 12 vdc and
24 vdc RU sets, and the other differences between the RU and the RU/GF,
I'll bore the list with a another write-up from my notes called:

            Differences Between RU-16 Through RU-19

                 12-vdc Versus 24-vdc Models

RU-16/GF-11 (12-vdc) components are identical to RU-17/GF-12 (24-vdc)
components except for the junction box, antenna relay, and dynamotor
units.  The RU-17 junction box CW-62018 contains A+ voltage dropping
resistors for filament power going to the 12-vdc receiver CW-46051A
and transmitter CW-52063A, the antenna relay CW-29076 contains a
24-vdc relay, and the dynamotor CW-21454A is designed for 24-vdc input.

The 24-vdc “blue-tag” RU-17 and GF-12 are actually wired for 12-vdc
filament power. 

Similarly, the 24-vdc “blue-tag” RU-19 is actually wired for 12-vdc
filament power, identical to the "black-tag" RU-18.  In these liaison
receiver systems, only the dynamotor and the junction box are
electrically different.


         RU-* (Liaison) Versus RU-*/GF-* (Command) Models

The RU-18 (12-vdc) or RU-19 (24-vdc) is designed to operate with
transmitters of the GO- or GP-series.  The junction box CW-62007A
(12-vdc) or CW-62017 (24-vdc) connects one or two receivers CW-46048D
and their control boxes CW-23087 to a common dynamotor unit CW-21215A
(12-vdc) or CW-21441 (24-vdc).  In contrast, there is never more than
one RU receiver in a RU/GF system.

RU-19 components are identical to RU-18 components except for the
dynamotor unit, and the junction box which contains filament voltage
dropping resistors.  The RU-18 or RU-19 junction box does NOT support
interface with a GF-series transmitter, nor contain circuitry specific
to use with ANY other transmitter.  The transmit/receive switching
takes place ONLY in the antenna circuit through the antenna relay in
the GO or GP transmitter.

The RU-19 manual states that the only earlier RU-series receiver with
which it is directly interchangeable is the RU-12.  Of course, the
CW-46048D receivers of the RU-18 or RU-19 are identical and
interchangeable.

The only circuit difference between the command set RU-16 or -17 (used
with GF-11 or -12) and the liaison set RU-18 or -19 is the source of
negative bias for the AGC stage.  The RU-16 or -17 derives this in the
dynamotor unit using a tapped resistor to ground in the negative HV lead
from the dynamotor.  The resulting bias voltage is routed from the
dynamotor base through the junction box, then to the receiver.

In contrast, the RU-18 or -19 runs the negative HV lead from the dynamotor
through the junction box and then to the receiver where it returns to ground
through a tapped resistor from which the AGC bias for that receiver is
developed.  

The AGC bias resistor is located in the receiver, instead of the dynamotor
unit, for the liaison receiver version of the RU is because in liaison
receiver service up to two receivers may be operated simultaneously from the
common dynamotor unit and junction box.  If a common bias resistor had been
used in the dynamotor negative HV lead in the dynamotor unit, as it is in
the one-receiver-only RU/GF command set models, the current draw of two
receivers through it compared to just one would greatly affect the bias voltage
generated.  Putting the bias resistor in each receiver assures that each has
only its HV current flow through it.  This maintains the AGC bias voltage
being generated the same regardless of one or two receivers being powered
from their common dynamotor unit.

Mike / KK5F