[time-nuts] Need info on HP 1 MHz ovenized XO

[GandalfG8 at aol.com]

Hi Ed
 
Can't help with the oscillator but the 74xx140 is a dual 4 IP Nand 50 ohm  
line driver, you'll probably find more data available if you search on 
74S140  rather than 74LS140.
 
Regards
 
Nigel
GM8PZR
 
 
In a message dated 13/01/2013 21:50:38 GMT Standard Time, eb at telight.com  
writes:

I want  to modify an old HP XTL oven for remote voltage tuning. The HP 
part number  is 0960-0079-1, made by Ovenaire (model OSC 49-14). These 
were used in  HP8443A tracking generators and probably other models too. 
It puts out 1  MHz, and is powered from +24VDC wrt the case ground. On 
opening it up I  found that the circuitry includes a 74LS73 dual JK FF, 
and a 74LS140 -  very obscure - apparently a dual 4-input gate of some 
sort. Since there  are two FFs available, it appears that the actual 
frequency of the crystal  could be 2,3, or 4 MHz. I'm guessing that it's 
3 MHz since there wouldn't  be a need for extra gate decoding if it was 
just a divide by 2 or 4.   I will measure and see, but I'd appreciate if 
anyone has any more info  about the guts of these oscillators, so I'll 
have more to go on for  modification and long term maintenance.

The fine frequency adjustment  is done with a ten-turn trimmer pot, so 
converting it to remote operation  should be fairly straightforward. The 
divider circuit board is outside of  the insulated XO oven, but still 
goes within the case. It also has the  external interface connections and 
the fine trimmer, so easy enough to get  at. I hope I won't need to 
modify the actual tuning range - I don't want  to crack open the oven  part.

Ed

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