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Thread: Crystals...

  1. #1

    Default Crystals...

    Long story short, I have a big box full of old and dusty 49MHz Motorola mobile radios and some have HUGE crystals. I don't mean a can of little cans made into a filter, i mean those big inch or so tall crystals. Seeing those and doing a little research, I found that it may be fairly easy to sand or etch them down and change the frequency significantly.

    I am very grateful there are old-timers with real tricks to share online! Never would I have imagined literally grinding a crystal down was something a hobbyist could do. I wish someone would write a radio book called "How we used to do things". Anyhow, this led me to a thought and I need some advice.

    Seeing how easy it was to change a large crystal, I started looking into changing the smaller, more common sized, crystals. There are videos online about it, but those techniques either involve adding pencil graphite or sanding it down (which eventually removes the deposited electrode).

    My question is this... Is there a way to recreate the electrode patch on a crystal in a home hobbyist setting without a vacuum chamber technique like a sputter gun or an evaporation boat? I am interested in changing some small crystals I have by 100kHz or so and know the electrode will be gone by then. Any thoughts? I'm not sure just "pulling" them will move the circuit 100kHz..

  2. #2
    Super Moderator 5B4AJB's Avatar
    Join Date
    Mar 2008
    Meneou, Cyprus


    I seem to remember reading somewhere you can "pull" crystals a few Hz by paralleling similar ones.

    Every time I manage to "de-lid" a crystal without breaking it, I break it good luck ;P

  3. #3


    I know adding a capacitor in series can pull it about 35kHz, but I need to go at least 100kHz. I think crystals stop operating long before that due to degraded Q. A dremel tool cuts the cans open nicely but I break almost every one as well, usually trying to put it back in the spring contacts.

    I've been debating chemically depositing silver as an electrode patch, but if I remember my chemistry, the plating solution produces azide after a certain amount of time. Silver nitrate isn't fun to play with either, I've stained a few fingers before. But, it seems like my only option at this point...

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