MASTR Pro Receiver Conversion for 220 Mhz

220 MHz conversion of GE MASTR Pro receiver by Peter Gailunas KA1OKQ

MODELS: 4ER41Cxx , 150.8-174 MHz
(xxODD) EG: xx= 11,13,15,17,19,21
Important must be ER41C

I highly recommend that you obtain a service manual for the ER41C series receiver. You can find them at flea markets or your local GE dealer for around $ 10.00.

Note: all capacitors are NP0 type ceramic disc.


Remove 1-3/4 turns from solder end of all six helical resonators (L301-L312).
Replace all removed taps at the same positions.
Note: A propane blow torch is useful for removing helical resonators from the copper plated casting. Cut resonators and reform the pigtail with wire forming pliers, clean capacitance hat of any oxide. Install newly formed helical and resolder with torch.

First mixer:
Remove C 1/2
Remove 1 turn from the top of L1

First osc:
Remove 1 turn from the top of L1.
Change C29/30 to 24pf (27pf N/G, 22pf ok).

Second Mult:
Remove 1 turn from the top of L1
Change C2/3 to 27pf
Change C10/11 to 3pf
Change C12/13 to 4pf (5pf N/G, 3 pf OK).
NOTE: (be very careful not to break c1 when removing cover on old rev's).

ICM Cat. # 021240Y

GE P/N 19A143191G1

Hook Up:
Wire system neg (pin 13) to gnd(pin1). Wire rx mute (pin2) to reg 10v(pin12). If multi-channel, connect +10v to desired frequency (pin 6,7,8 or9). COS is available at pin 19 it transitions high on signal. I use this line to drive an open collector 2n2222 for buffered cos. Use 10k in series with the base of 2n2222.

Volume pot is 250 ohm. Squelch pot is 2.5k or 3.5k (Use of other value pots results in unpredictable squelch operation).

Load AF output with 4 ohm 5 watt (AF amp may oscillate without it).

as per GE pub. LBI-3867P

12DB SINAD @ approx -113dBM/.5uV

Power supply:
It's ok to use 13.8 in place of 10V. I have found this to work fine save yourself a regulator.

Audio out:

Take repeater audio from the high side of the vol pot. The audio will be pre-emphasized at this point. De-emphasize as required or inject directly into modulator of your exciter(that's MODULATOR not normal audio input of the exciter). This yields retransmitted audio as good as the signal transmitted to the repeater.

If local speaker is not required remove audio output stage as follows.
Remove r40 220 ohm 1/2 w
Unplug wires from J13,14,15,16 ON audio/squelch board.

Ground J15
Take audio from J14

A word about receiver sensitivity:
These receivers when properly modified should meet the sensitivity spec. I have run the Advanced receiver research GaAS FET preamps with excellent results. I cannot recommend the use of other makes of preamps.

This conversion info was developed for the early days of the NEW ENGLAND NETWORK (1980). The net covered most of New England on 220 mhz. The system was way ahead of its time. Little, if anything,remains today of the system.

Thanks to:
Sergio Marino KG1C and Dave Tessatore K1DT for their help in the development of this conversion info (mid 1980's)

Peter Gailunas/KA1OKQ

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