[time-nuts] Ancient OCXO in scope calibrator.

[David C. Partridge]

Nuvistor is NOS, and I've tried swapping them.

Circuit has anode (plate) connected to a 50MHz tuned tank.

G1 is connected to ground via a 100K resistor, and to the cathode via the
crystal and trimmer cap.

Cathode connected to ground via a ferrite tunable slug inductor (6-10uH)
close to a similar one also 6-10uH.  The second one has 100K in parallel
with 1nF to ground, and 15pF across the inductor.   The second one has a
pick off coil of a couple of turns which sends the signal to the countdown
board.

The full schematic is in the Tektronix 184 manual on BAMA which is in djvu
format.

Cheers
Dave

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bruce Griffiths
Sent: 07 September 2008 23:38
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Ancient OCXO in scope calibrator.


> Dave
>
> Need a few more circuit details.
> The crystal current wont be very high unless their are other 
> components connected to G1.
>
> Bruce
>
>   
The anode G1 capacitance is about 10fF so with 25V rms at the anode, the
crystal current would be around 16uA if the circuit relies on feedback via
the anode to grid 1 capacitance.
This seems to be a little low to be useful.
You could try substituting a newer 7587 there are several currently
available on ebay and elsewhere.

Bruce


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