How to convert GE MASTR series radios from 450 to 425 MHz

Three items need to be addressed:

1. Helical front end [L301, L302, L303, L304, L305] needs more inductance. Open the bottom of the front - end and take out the American Beauty [150W] and unsolder the 5 coils. Using #10 solid copper, make a one third turn coil to match the coils that were taken out. Take off the enamel on the end of the original coil and solder the 2 coils together. After soldering the coils into the chassis, be sure to align the coils (by bending).

2. Next is the oscillator / multiplier which needs a lot of work! Pull the oscillator board out since it will be easier to work on. Solder a wire from H7 / F1 / brown wire to ground. Pull the brown wire off the board. This is the F1 crystal ground. Unsolder the white wire at H3 and fold it back with a tie. Make a jumper and short the 10v trace (red) to where the white wire (receiver oscillator control) was attached. Add a 2-4 pico farad capacitor across C407. Run a 7” wire from H6 / blue wire / compensation line to P903, pin 5. A FB slipped over pin 5 is great. On this wire install a ferrite bead - (low frequency type). Install two chip capacitors (.001 - .01 uF) near channel element on the 10 volt line and the compensation line to ground. Disc caps – OK. Install another chip (.001) at R419 to ground. Install a .01 chip capacitor on the channel element – pin 4 to ground. The compensation line really radiates RF.

3. Next is the preamp. Install a 10uF Tant. Cap across C2308. Install a .001uF chip capacitor across C2307. Unsolder the metal shield on L2301. Solder a small solid wire (resistor wire) at the top where it is folded over and will form an X - capacity hat.

For Reliability:

Resolder : crystal –ch. ele., 6 pins on ch. Ele., 6 pins ch. Ele. on osc board

7 pins, J602 and 7 pins P903 / IF DET. Board

Stabilant : 6 pins / ch. ele. , 7pins / J602, 7 pins / P903, 5 screws on preselector ( L301 – L305 ) , 3 screws ( L306 – L308 ) osc / mult.

Info:

Osc / mult board @ 425 mhz, Hi side inj. Xtal = op. freq.+ 11.2 / 27

L401 - 3X 48.46 mhz

L402 - 3X 145.4 mhz

L407 - 3X 436.2 mhz

Compensation range: -10 to 50 degrees C, 3.7v to 4.3v

****** For best (lowest) distortion*******

Always pick the IF det. Board that has the adjustable IF cans and not the fixed inductor boards. These boards let almost 4 ¼ Khz dev. pass verses about 3 Khz for the fixed inductor.