[time-nuts] Ancient OCXO in scope calibrator.

[Brooke Clarke]

Hi Dave:

Do you have a photo?

It's been my experience that older electronic equipment fails because of poor 
connections rather than bad components.  For many examples see:
http://www.prc68.com/I/HaT.shtml

Have Fun,

Brooke Clarke
http://www.prc68.com/P/Prod.html  Products I make and sell
http://www.prc68.com/Alpha.shtml  All my web pages listed based on html name
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam

David C. Partridge wrote:
> 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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