GE Mastr II Modifications for 220MHz
Model MX56KAS66A

This was originally written a long time ago and I recently found it in a file. So here it is for the world to have just in case someone actually needs to mod a MASTR II. I take no responsibility for the following. This is presented as a public service.

de WB6RHQ - 20 January 1989 - Rev A


A. Oscillator Multiplier Board 19D423241G1

1. Replace C412 with 12pF.
2. Remove C421 and C417.

Q401 is now x2, Q402 is now x2. Q401 was x3 and Q402 was a buffer stage. Frequency multiplication range is 17MHz, 106MHz, 212MHz plus the IF frequency of 11.2MHz for 220MHz.

New Crystal Formula is:

xtal = (f - 11.2) / 12
example: 17.675MHz = (223.30 - 11.2) / 12

B. Mixer Board 19C320153

1. Short out one turn from the top and one turn from the bottom of L502.

C. RF Assembly 19D416693

1. Remove 1-3/4 turns from each helical resonator.


A. Exciter Board 19D416859G1-G4

Crystal formula is the same as the original high-band version.

xtal freq = f / 12
example: 18.741667 = 224.90 / 12

1. Replace C144 with 4pF.
2. Replace C167 with 15pF.
3. Replace C149 with 5pF.
4. Replace C154 with 6pF.
5. Replace C155 with 3.3pF.
6. Replace C157 with 3.3pF.
7. T108 3-3/4 turns; 1/8" turn spacing
8. T109 2-3/4 turns; 1/8" turn spacing
9. T110 2-3/4 turns; 1/8" turn spacing
10. T111 3-1/4 turns
11. T112 3-1/2 turns

B. Power Amplifier 19D416936G1 (35 Watt version)

1. Remove C228, C230, C243, C244, C246, C263, R207 and L209, L210, L211, L213 and K201. (Remove K201 for repeater service only)
2. Replace Q203 with a PT8874A.
3. Replace C212 and C213 with 70pF uncased mica.
4. Replace C218 with 10pF uncased mica.
5. Replace C220 and C221 with 150pF uncased mica.
6. Replace R208 with a 0.68uH inductor.
7. Install a 10 ohm, 1 watt resistor from the base of Q203 to ground.
8. Install a 47pF uncased mica from the intersection of R203, L201 and T201 to ground.
9. Install a 1K 1/4 watt resistor and an ARCO 404 from the intersection of CR201 and T201 to ground.
10. Install two 50pF chip caps from the base of Q202 to ground. Caps should be installed next to C212 and C213.
11. Install an ARCO 404 from the collector of Q203 to ground.
12. Install an ARCO 404 from the intersection of C231 and T204 to ground.
13. Install a 43pF chip cap from the collector of Q203 to ground.
14. Remove trace between L209 and L208.
15. Remove trace between L211 and L210.
16. Install jumper to bypass the T/R relay from the trace going from L213 and the "ANT" connector. (Repeater service only.)
17. Replace L209 with a #18 jumper.
18. Install a 7pF uncased mica from the L209 jumper to ground.
19. Replace L212 with a #18 jumper.
20. Install a 7pF uncased mica from the L212 jumper to ground.
21. Cut the trace between C245 and L211.
22. Install a coil, 4 turn #18, 1/4" diameter, between L211 and L212 and between both shields inside the low pass filter assembly.
23. Install a 15pF uncased mica from the center tap of the coil, described in step 21, to ground.