The 3455A is a really nice unit if you are looking for a digital voltmeter/multimeter that is really accurate, and if you don’t want to spend too much. These units go for about USD 100 to 150, not bad, considering their performance – 6.5 digits.
This unit just needed some de-dusting, and was missing some screws. Build some time early 1979 (judging from the data codes, rather than the serial number), this unit doesn’t seem to have hand any issues over the last 35 years – while in service at Northrop Grumman.
For a bit more through test, the 3455A was monitored for about 1 hour, with a low noise 9 V source at the input, and the differences logged.
Apparently, the 3455A is about 6.7 ppm low, vs. the 34401A. Which one is right, I can’t tell – the 34401A stability specification is about 20 ppm, after 90 days, far worse than the difference of the two meters.
The 3455A has a 11177B reference assembly. It has option S01 – no idea what option this is. HP P/N 03455-66520 Rev B.
The active part, a HP 1902-0926 thermostated Zener – very similar to the LM399, but not in the typical isolated (white) case. One thing is for sure, this part is now well aged!
The reference assembly has some remarkable 0.01% tracking resistors, with 1 ppm tempco – it doesn’t get much better even nowadays, and the resistors are in hermetically sealed cans, with glass seal, except one 1.0020 k +-0.01% resistor in the red resin package.
AC measurements were also carried out in the 10 Hz to 500 kHz range – it seems the 3455A even outperforms the 344401A for flatness, especially at the low end of frequencies.