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changing crystal for another freq.

G

gr229

I have this transmitter that is the freq is set by an non oven crystal. set at 99.9 I want change to 101.7-102.1 any freq in that range. I tried adjusting the freq. with the installed resistor pod but that only change the freq a few khz. I was told I could not "bend" it that far.

Once I acquire the correct crystal for the desired freq.,

1) will it install without retuning? stretching coils?
2) will I have to replace any caps, transistors, IC's?
3) is there more than 1 crystal to replace for the desired freq.?
4) most likely I will send it out to have it done, just curious

Thanks you for any knowledge with this.
 
Ok, dont take this for gopel.
I retuned a crystal controled tube exciter and later a solid state one years ago. Before you change the crystal take some readings on the oscillator so you know when the oscillator is oscillating with the new crystal. Once the new crystal is installed use a FM receiver to determine if it is oscillating. You'll probably have to place the receiver very close to the unit. Assuming you find the carrier then swing the frequency to that you want to operate at by adjusting the variable resister for that purpose. Always record where you started i.e. how many turns counter clockwise or clockwise etc on any component you are adjusting. so you can go back later if you fubard. If you can't get there you may find a capacitor afixed across the crystal. If so you may have to juggle it's values to get the crystal to move up or down the band. Or install a variable capacitor and rock it to the desired frequency. You'll need a frequency counter to know when your on the channel you wish. Once you are on frequency and only if you arn't makiing the power you had with the previous crystal, try rocking the tuning stages after the oscillator while watching the power level on a watt meter on the output hooked into a dummy load. You should be peaking for highest power on the meter. Caution, don't rock the stages very far. With tube exciters it's relatively easy to retune. With a solid state unit be more carefull. You may find that you just can't get to the frequency you want bacause some modules are only for a portion of the band. OR,,,,,,,just send it in.
 
Are you using this for a full power station or just to mess around with?

If it's for a full power station I'll tell you to dump it and get anything more modern. Even a Bext will run rings around it in audio quality and stereo separation.

If it's just for fun, since it isn't very far away that you want to go, you should (I repeat, should) be able to replace the crystal and with minimal retuning get it to work on the desired freq.

Check any filtering on it to see how sharp the cutoff freq is and where it is.
 
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