[volt-nuts] Motorola buried zener

[Mike S]

At 10:06 PM 9/12/2009, Bruce Griffiths wrote...
>The reference amplifier(U2) on A4 reference board circuit in the 732A
>appears to be compatible with one of the Motorola 6.8V reference
>amplifiers such as the MCA1914N, MCA1924N or MCA1934N.
>The only difference between these is the specified operating 
>temperature
>range.
>If the oven temperature is around 50C then a selected MCA19124N is 
>likely.
>They had a maximum voltage change (Iz = 5mA) of 5mV over the 0-75C
>operating temperature range.
>Reference voltage was 6.8V with a 10% tolerance.

That sounds right. That's about 10 ppm/C tempco. Any idea what 
Motorola's spec was for long term drift? 732As had a mean drift rate of 
~0.5 PPM/yr., according to Fluke (about 4x better than the LTZ1000 
spec!), and a tight deviation, both much better than the newer 732Bs .

BTW, these types were used by Fluke at least through the early '90's, 
in the early 732Bs, so I don't know that calling them "ancient" is 
fair.