Sensitivity Alignment - The R-390A Frequently Asked Questions Page

sensitivity and alignment notes page 16
slug heights. To have the receiver work properly, this whole assembly must be
"timed."
Here is how to check:
First and formost, the PTO must be 1 mHz long. To check this, zero beat the
calibrator and use the ZERO ADJ to set the odometer readout to the bottom of the
PTO's range or, XX (-) 000. Run the KILOCYCLE CHANGE control to the top of the
PTO's range or XX (+) 000 and note the frequency the odometer reads when zero
beat. The difference between the indicated frequency and XX (+) 000 is the error. For
the receiver to work properly, the error must be less than about 1KC.
If the error is more than 1KC, you must perform the end point or "Variable-
Frequency Oscillator End Point Adjustment." In the Army manual I have, it is
outlined in paragraph 81 on page 119.
There are pictorials involved and I cannot post this procedure here. The Hollow
State News may have some reprints available for those who do not have a manual
but feel they can perform this procedure.
Do not proceed further until the PTO end points are correct.
Zero Beat the CALIBRATOR to WWV. This is easily done by first using the BFO to
zero beat the receiver with WWV. Then, turn the FUNCTION control to CAL then
adjust the calibrator capacitor through the rear panel and adjust for zero beat.
Next, set the ZERO ADJ clutch to the center of its range. Disengage the clutch by
turning the ZERO ADJ knob CW. Rotate the KILOCYCLE CHANGE control to the
CW stop. Make a note of its position. Then, rotate it to the CCW stop and again,
note its position. Finally, set the knob 1/2 way between these two points.
Set the KILOCYCLE CHANGE and MEGACYCLE CHANGE controls so that the
odometer readout indicates >exactly< 07 + 000. (The receiver would actually receive
an 8 mHz signal at this point). Engage the DIAL LOCK.
Turn the receiver upside down so that the PTO and oldham coupler can be accessed.
Turn on the BFO and CALIBRATOR. Using the appropriate bristol spline wrench,
loosen the >forward< clamp on the oldham coupler. Rotating the coupler will cause
the PTO shaft to rotate and change frequency but the readout will stay the same.
Zero beat the calibrator and retighten the screw. (NOTE: You should not have to
move the oldham coupler more than 1/2 turn in either direction to achieve zero
beat).
Check the dial over run by turning the KILOCYCLE CHANGE control up in
frequency past 000. It should stop at 035. DO NOT USE THE ZERO ADJUST KNOB
TO ALTER THE READOUT. It it does not indicate 035, you will need to adjust it
when once the front panel is down. This is a little complicated. First, breaking the
bristol-spline cap screw loose on the gear clamp which drives the odometer readout.