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CONTROL GRID GROUNDING CAPS
USED ON LATER PRODUCTION WESTINGHOUSE MODEL 823
Due to certain changes in the design of W6A8 Radiotrons having been made, there is a possibility of a
parasitic oscillation at high frequency being set up continuously in the W6A8 Radiotron in Model 823. This
parasitic oscillation will result in a continuous hissing noise being heard in the receiver. Receivers now in the
field with the former style W6A8 Radiotron will be satisfactory, but if the W6A8 Radiotron has to be changed
for any reason, and is replaced with one of the latest design, it is possible that this undesired oscillation may
result.
If this occurs, order from the nearest Canadian Westinghouse Company, Limited, District Service
Department, a control grid grounding cap S. No. H-38327, list price $ .25.
Some of the later production Model 823 receivers will be shipped already equipped with this control
grid grounding cap. To install this part, simply cut off the present control grid lead to the W6A8 Radiotron,
close to the chassis, and clip the grounding cap in place on top of the tube.
REPRODUCER USED ON LATER PRODUCTION, MODEL 823-Z
The reproducer used on the first production, Model 823-Z, was marked "S. No. H-38175."
Later
production used a speaker marked "S. No. H-38291." The parts of these speakers are not interchangeable
IMPORTANT INFORMATION ON REPLACEMENT PARTS
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The first production run of these models
(as
will be noted from the chassis serial plates) are all
designed to operate on either 25 or 60 cycles.
110 volts.
It will be noted from the schematic circuit
diagram and the chassis wiring diagram that there is no centre tap brought out on the heater winding
of the power transformer. The replacement transformer (S. No. H36335) will however, have a centre tap,
which should be taped up and not used when the transformer is installed on a chassis from the first production
run.
The second production run included some chassis which had a 60 cycle only power transformer. These
are so marked on the chassis serial plate. This power transformer is S. No. H-38239, list price $6.90.
The power transformers on all of the second productiun run have a centre tap on the heater winding,
which is connected to the chassis frame, and none of the heater contacts of the tube sockets are connected
to the chassis frame as shown in the schematic circuit diagram.and the chassis wiring diagram, but connected
directly to the heater winding -
The 60 cycle transformer is smaller than the 25-60 cycle transformer and should it be necessary to install a
25 cycle transformer on a 60 cycle xnodel, the service man will need to cut openings in the top surface of the
chassis in the proper location to fit the larger transformer.
MODEL 823-Z
LATE PRODUCTION
On some of the 823 -Z's, the "IF"
amplifier secures its plate supply from the
positive end of the resistor R-6 instead of
from the negative end of this resistor. This
change reduces the total current flowing thr-
ough the resistor R-6, decreases the voltage
drop and increases the target voltage on the
tuning indicator to give a more uniform color
to the fluorescent screen.
A.V.C.
VOLTAGE
AND
6G5
CONTROL
VOLTAGE
2.2 MEG.
56000A
220000 .
TO
VOLUME CONT'L
CIRCUIT
ONE
DIODE
OF
6H6
2.0V.
.
R-23
R-22
15n
20"
Detail of AVC Circuit
Note; (1; The A.V.C. and tuning indicator control voltage (with respect to chassis frame) is the sum of the voltage, A, and B,rectified
by the two diodes of the W -6H6 plus the 2.0 volt residual bias from the voltage divider R-22, R-23.
Note: (2, This use of the A.V.C. voltage doubling circuit is a new application for the W-6H6Radiotron, and occasional Radiotrons may
be found that are 4uite satisfactory for ordinary service but develop a hum when used in the Model 823. The remedy, of course, is to
interchange W -6H6 Radiotrons and use the one removed from the Model 823 in some other model which does not use the voltage
doubling A.V.C. circuit.
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