Instructions for Converting a High Band GE MASTR II to 222 Mhz
by Mark Gilmore, WB6RHQ

High-band MASTR II Exciter on 220Mhz (19D416859C4)


Remove the cans from the T108, T109, T110, T111 and T112 coils. Remove the T111 and T112 coils and save them.

Remove and discard the T110 coil.

Remove the T108 and T109 coils and install them in the T111 and T112 positions. 1/4 turn needs to be removed from the coil that goes into the T112 position to maintain continuity with the PC board traces.

Remove all but 3 1/2 turns from the original T111 coil and install it in the T109 position. Remove all but 2 1/2 turns from the original T111 coil and install it in the T108 position.

Replace the following with the new values shown:
C144 - 6.2pf
C145/167 - 5.1pf
C148 - 3.9pf
C154 - 13pf
C155 - 6.8pf
C157 - 22 pf
R143 - 470 ohm 1/4 watt

Remove the following parts:
R152 (May already be missing)
R1 (Part of T110 assembly)

Replace R147 and C149 with a jumper wire.

Install a 1.8k 1/4 watt resistor, from the base of Q109 to the intersection of L106 and C152, on the bottom of the board.

Replace L108 with a 100 ohm 1/4 watt resistor.

Reinstall the cans on the T108, T109, T111 and T112 coils. Discard the can from the T110 coil.


1) Q108 is now a tripler instead of a doubler.

2) The new crystal formula is xtal = f/18. The original formula was xtal = f/12. Calculate the fundamental, put it back into the original formula, and order the equivalent high-band frequency. The International Crystal catalog number is 021410.

High-band MASTR II Power Amplifier on 220Mhz 19D416936G1 (35 watt version)

Amplifier Modifications

Remove C263.

Install a 47pf uncased mica from the intersection of R203, L201 and T201 to ground.

Install a 1K, 1/4 watt resistor and an ARCO 404 from the intersection of CR201 and T201 to ground.

Remove R207.

Replace C212 and C213 with 120pf uncased micas.

Replace C218 with a 10pf uncased mica.

Replace C220 and C221 with 150pf uncased micas.

Replace Q203 with an MRF1946A or an SD1022.

Replace R208 with .68 uh

Install a 10 ohm, 1 watt resistor from the base of Q203 to ground.

Install an ARCO 404 from the collector of Q203 to ground.

Replace C228 with a 43pf uncased mica.

Replace C230 with and ARCO 402.

For repeater service, remove K201 and install a jumper to bypass the T/R relay between the traces going to L213 and J203.

Low Pass Filter Modifications>

Remove the trace between L208 and L209.

Remove the trace between L210 and L211.

Replace L209 with a #18 jumper.

Install a 6.8pf uncased mica from the L209 jumper to ground.

Replace L212 with a #18 jumper.

Install a 6.8pf uncased mica from the L212 jumper to ground.

Remove L208, L210, L213, C243, C244, C245 and C246.

Install a coil, 4 turns - #18 - 1/4" diameter and 1/8" turn spacing, on the PCB foils going to L209 and L212 between both shields inside the low pass filter assembly.

Install a 15pf uncased mica from the center tap of the coil, described in the previous step, to ground. It is easier to install the capacitor and then the coil.

High-Band MASTR II Receiver on 220 Mhz

Oscillator Multiplier Board (19D423241)

Replace C412 with 12pf.

Remove C421 and C417. C421 and C417 may already be missing.

Install a jumper from the center of L403 to the next turn of L403 closest to R404.

Install a jumper between the bottom two turns of L403 closest to the position reserved for C418.

Q401 and Q402 are now frequency doublers. Q401 was a tripler and Q402 was a buffer stage.

The new crystal formula is: xtal = (f - 11.2) / 12 example: 17.675 = (223.30 - 11.2) / 12

Calculate the fundamental frequency, put it back into the original formula and order the equivalent high-band frequency. The International Crystal catalog number is 021420.

Mixer Board (19C320153)

Install a jumper from the bottom center turn of L502 (closest to C504) to the next turn towards the center of L502.

Rf Assembly 19D416693

Remove the helical resonators:
L301/311, L302/L312, L303/313, L304/314, L305/L315, L306/L316 and L307/L317.

Remove 1 3/4 turns from the cold end of each resonator and reinstall. A soldering iron in the few hundred watt range is required to complete the procedure.

220 Mhz MASTRII Modification Parts List

1 - 3.9pf
1 - 5.1pf
1 - 6.2pf
1 - 6.8pf
1 - 13pf
1 - 22pf
1 - 100 ohm 1/4 watt
1 - 470 ohm 1/4 watt
1 - 1.8K 1/4 watt

1 - 12pf

Power Amplifier
2 - 6.8pf uncased mica
1 - 10pf uncased mica
1 - 15pf uncased mica
1 - 43pf uncased mica
1 - 47pf uncased mica
2 - 120pf uncased mica
2 - 150pf uncased mica
2 - ARCO 404 trimmer
1 - ARCO 402 trimmer
1 - .68uh
1 - 10 ohm 1 watt
1 - MRF1946 or SD1022
1 - 1 foot of #18 wire

220 Mhz Conversion Performance Notes

The following nominal voltages should be measured across these components:
R209 - 56 mv
R210 - 14 mv
L203 - 89 mv

Measurements were made assuming .2 watts input and R219 adjusted for 30 watts output.

The exciter should deliver 200 mw output plus or minus 1db.

The receiver should meet or exceed original factory high-band performance of .35 uv SINAD

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