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137.9KHz to 137.8KHz crystal pulling

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neazoi

neazoi

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Hi, I have found a vintage (7-pin glass tube like) 137.9KHz crystal and I need to pull it down to at least 137.8KHz (and even lower).

Would I be able to pull this, 100Hz lower at this low frequency, or they are dead stable?
 

Without knowing the specific crystal you are using, the general answer is that you can pull a crystal, within limits, both high and low.
After all the equivalent circuit for a crystal is a resistor, inductor and capacitor all in series, and in parallel with a capacitor. Therefore you can put additional capacitance next to the crystal (exactly where depends on the circuit) to pull it slightly.
You are looking for a very small variation so this should be possible although you probably need a very small variable capacitor and some minor adjustments to get it to the frequency you are after.
Susan
 

According to literature, pull ranges of up to 1000 ppm, are possible with LC circuits.
 

neazoi said:
Hi, I have found a vintage (7-pin glass tube like) 137.9KHz crystal and I need to pull it down to at least 137.8KHz (and even lower)...
Click to expand...

Some of them, you can see the small crystal mounted (actually hanging) between two electrodes (in the middle of the tube). What are the 7 pins doing in a crystal?

Some of these are very high Q crystal and may refuse to work at other frequency (but you can always try).
 

The 7 pin base, was a very common base in the vacuum-tube days.

And it was used as a general purpose connector for many other things.

Think of the DB-9 plug; its intended use is for RS232 but has been used for other applications.
 

Yes you will.
As FvM got it righ you should be able to pull it 137Hz. This will probably require a series L or series LC
 

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