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

[Ed Breya]

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