This step of two transistors has a high input impedance due to the use of FET. We can use BF245 for this function and the bipolar can be BC548. The circuit is from an 1975 American documentation.
We found this circuit in the 1994 Linear Applications Handbook by National Semiconductor. The...
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
Texas Instruments REF33x Voltage References can be obtained from Mouser Electronics. These small...