[ARC5] Crystal work-around question. OT

[Kenneth G. Gordon]

On 23 Sep 2020 at 18:26, J Mcvey via ARC5 wrote:

> 
> The crystal in question is a sealed HC25U type.
> The frequency is low by about 400 Hz, so it can't be padded. Could it be "brought 
> up" with an adjustable series cap?
> I have a new one on order, but was wondering if anyone had a "fix" without 
> replacing the crystal?
> 
> I suspect too much 'pulling" would cause instability if there was a way.
> What say you guys?

A series cap will sometimes work. It usually has to be of much greater capacitance than a 
parallel cap which is used to LOWER the frequency. As I remember it, the series cap must 
be on the order of 10 times the value of a parallel cap for the same "movement'.

Also, as you say, instability will result if you try to move it very far. However, 400 Hz is 
reasonable.

Try it and let us know the result.

Ken W7EKB