[time-nuts] Ancient OCXO in scope calibrator.

[David C. Partridge]

A completely unused (had to open the perforations on the plastic bag inside
the box) NOS nuvistor substitution made no difference to the effect of
probing.

D. 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Neon John
Sent: 10 September 2008 01:20
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Ancient OCXO in scope calibrator.

On Tue, 9 Sep 2008 19:19:39 +0100, "David C. Partridge"
<david.partridge at dsl.pipex.com> wrote:

>Following the good advice I received about increasing the value of the 
>trimmer capacitor, I replaced the trimmer which was originally 3-12pF, 
>with another one which was 2-22pF.

I would leave the same trimmer in there and shunt it with a fixed 10pF cap.
That way the adjustment won't be so touchy.

>Still don't understand why probing with a 10Meg, 1pF load kills the 
>oscillation stone dead until the next power cycle.

That says that the circuit had just enough gain and positive feed back to
oscillate but just barely.  I'd have to see the circuit to recommend
changes.
The root cause is probably lost gain in the tube but that can be compensated
for.

I was just sitting here thinking about the oven problem.  If you replace the
thermostat with the proper power PTC thermister, you could make the oven
linearly regulate at a single temperature.

John
--
John De Armond
See my website for my current email address http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Multitasking: Reading in the bathroom!


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