7.7975 MHz crystal - Where to find one?

[Lkaskel]

Hi Everyone,
I have a Robyn SB520 that I am repairing and the 7.7975 crystal is bad. How do I know you asked? Well, I could not get it to give a stable frequency during alignment so I swapped it with one from a known working radio and it aligned perfectly. I then took the "bad" one and put it in the working radio and it would not give a stable frequency. I have searched the interweb and called a few suppliers like Ken's and none are available. Aany ideas where I could get one?

Also, I need 1 knob for the 520. The radio is missing one......

Thanks as always!!!

 

[nomadradio]

That's a bug hunt. Turning over rocks is pretty much your only hope. That crystal is effectively a custom-made part. And having a replacement made might produce the result you need, or might "almost" adjust properly to the desired frequency.

73

 

[brandon7861]

I have one.

 

[brandon7861]

I originally wrote about kens having the 7.7985 crystals and that they would work by adding a series inductor pulling them down, but I deleted it when I realized I had my captain morgan calculator out (regarding the amount of pulling needed, decimal places move on me when I drink and do math) and that it may be possible to move it down 1kHz without the added inductor.

But no need to mess around, I can part with mine from the stalker if you still need one. Its got the fatter socket-style legs and tested good a test oscillator.

 

[nomadradio]

Pretty sure it's in a socket on that circuit board.

73

 

[TM86]

Worst case scenario, and this pretty much a desperation move, set up a Si5351 for that frequency and use that as a crystal replacement.

It would require modifying the oscillator to be more of a buffer amp and some support circuitry around the Si5351 to get a more sine wave looking signal, but when you've got nothing left to lose it's an option.

 

[nomadradio]

Hmm. Retrofit of the future. A Si5351 on a tiny pc board with a 8-pin controller chip. It gets uploaded with the frequency or frequencies desired. Individual input wires select one frequency of two, or three, or whatever.

You'd think somebody out there is working this up, or has already.

73

 

[brandon7861]

You'd think somebody out there is working this up, or has already.

73

Somebody has, and this is why I have removed them from my amazon cart three times now. I need constant reminding. Link cuts to the part showing the signal it produces. There is jitter in both phase and amplitude, high in harmonics, it requires lots of signal conditioning to even be useful in a CB radio (unless you want all that going into your mixer).

 

[brandon7861]

M0XFX used one in this video (with a bandpass filter) on an old radio and it worked good, but thats a lot of stuff needed to replace 1 little crystal.

 

[TM86]

M0XFX used one in this video (with a bandpass filter) on an old radio and it worked good, but thats a lot of stuff needed to replace 1 little crystal.

Which is why I called it a worst case scenario. It would be better to buy a junker 858 chassis and steal the crystal out of it. But eventually even those won't be available. No junkers and no source for new, you do what you can.

 

[Lkaskel]

I originally wrote about kens having the 7.7985 crystals and that they would work by adding a series inductor pulling them down, but I deleted it when I realized I had my captain morgan calculator out (regarding the amount of pulling needed, decimal places move on me when I drink and do math) and that it may be possible to move it down 1kHz without the added inductor.

But no need to mess around, I can part with mine from the stalker if you still need one. Its got the fatter socket-style legs and tested good a test oscillator.

You are very kind for the offer!!! I sent you a PM.

Thx so much!!