[Boatanchors] Disc caps vs paper caps

[james.liles at comcast.net]

Hi John, Ian:

I believe there is a possibility that chirp may have been caused by using a 
high K Ceramic cap either in the key click circuit or in the tuned loop. 
Using a high K Ceramic cap in a resonant circuit is a bad idea because the 
capacity varies with voltage --- deadly if you key the oscillator.

I believe the National NCX-5 had key clicks because they used a class 3 
ceramic cap in the key click circuit --- may be wrong --- never owned 
one --- someone know?

Kindest regards Jim K9AXN


------------------------------------- ORIGINAL 
MESSAGE --------------------------------------
Message: 5
Date: Thu, 27 Sep 2012 11:02:28 -0700 (PDT)
From: "J. Forster" <jfor at quikus.com>
Subject: Re: [Boatanchors] Disc caps vs paper caps
To: "Ian Wilson" <ianmwilson73 at gmail.com>
Cc: "Boatanchors at mailman.qth.net" <boatanchors at mailman.qth.net>, Mark
Foltarz <foltarz at rocketmail.com>, Glen Zook <gzook at yahoo.com>
Message-ID: <1448.12.6.201.39.1348768948.squirrel at popaccts.quikus.com>
Content-Type: text/plain;charset=iso-8859-1

Prove it.

-John

================



> I have noticed enormous amounts of drift in Colpitts-type crystal
> oscillators using some
> types of ceramic capacitors in the loop. This resulted in significant
> chirp
> on each key down.
>
> I don't know whether this is due to some form of self-heating, but the
> capacitance changes
> were so large that I can readily imagine that if you scaled the values up,
> and used these
> capacitors in an audio coupling network, that you should be able to detect
> the nonlinear
> change of time constant with input readily enough using both normal ears
> or
> some sort
> of audio spectrum analyzer.
>
> 73, ian K3IMW