Metering Jack Diagram|
You don't need to use the GE test set to tune up a MASTR II. In fact, we have
never used one at all. You can get by with a sensitive voltmeter.
An analog meter will work fine, provided it is of fairly high input impedance.
We always use DMMs. If you have a DMM with a bar-graph display, in addition to
the digits, so much the better. The key to using a DMM is to make all adjustments
slowly, so you are not subject to the relatively long hysteresis of the
meter. You will typically use the 200 mV, 2 V, and 20V scales on your DMM to
align the radio.
Most of the measurements on the metering jack are measured against A-, which
is accessible at pins 8 and 9 of the metering jack. Metering position G appears
to be the exception, and is measured with metering jack pin 5 as the low (-) side
and metering jack pin 6 as the high (+) side. This difference rears its ugly head
in the VHF-hi exciter, where the GE test set is referenced to A+ rather than A-.
We recommend that when aligning VHF exciters, unless you know exactly what
you are doing, you place both multimeter leads as indicated in the diagram for
reading metering position G. This does not apply to the GE test set.
Connecting to the metering jack itself may involve some creativity. The
socket holes are a somewhat inconvenient size. We
have used large canvas needles, heavy resistor leads, even brass tacks! Make
sure that whatever you stick in there cannot fall out and short something out
in the radio.
The diagram above shows the pinout of the metering jack. The letters next
to the jack indicate the GE test set measurement position that appears on the
adjacent pin. These letters are referenced in the service manuals, not the
pin number. A, B, C, D, F, and G appear to be the most commonly used
measurements on the MASTR II (based on a quick survey of three service manuals.)
In the unlikely event that your manual references E, I, or J, you will need
to consult the schematics to see which pin number is used. (Please let me
Most (or all) of the adjustments in a MASTR II are relative, as opposed to
absolute. The adjustments involve either peaking or dipping a
specific metering jack reading by adjusting one or more controls, usually
variable inductors (coils) or variable capacitors.
Peaking an adjustment is relatively straight forward: tune the specified
controls to get the largest reading on the meter. You may need to change the
voltage range selected on the meter during this process. If you cannot find a
peak, it is likely that an earlier stage in the radio is not properly aligned.
Back up one or two steps and make sure that the previous stages are correctly
Beware of "false" dips and peaks. Sometimes you will find a control that exhibits
the desired dip or peak more than once in it's adjustment range. Usually the most
pronounced (bigger) dip or peak is the correct one.
Dipping can be a bit trickier. The idea here is to find the low reading
for the specified controls. Sometimes, the dip will be somewhat shallow. This
is usually OK. If you can't find a dip, then backtrack like above.
When aligning transmitters, do not leave the transmitter keyed
(transmitting) for an extended period. Connect the meter, key up, make your
adjustment, and unkey. It is possible to damage the exciter during tune-up while
it is not properly aligned. Be sure a dummy load is connected to the transmitter
output during alignment and testing.