Time Electronics 404S & 404N DC Millivolt Source Teardown & Review

Here we review two Time Electronics Ltd. DC Millivolt Source calibration units. They use a precision reference zener diode, low temperature coefficient resistors and thumb switches to select a precise voltage accurate to 1 Micro Volt. They have 3 ranges and an accuracy of ± 0.05%.

4 thoughts to “Time Electronics 404S & 404N DC Millivolt Source Teardown & Review”

  1. No pre-aged zenner diodes or chopper op amps in the sealed module. One MAX63** voltage reference and
    one OP07 op-amp. A few driver transistors in dc configuration and that was about it. I know because I have the circuit diagram.

    Ex Merchant Navy Calibration Engineer.

  2. Mr Scully – I’m trying to refurbish a 404N that has had a number of issues, mainly with the batteries going pop inside the holders (fortunately new holders are available) and the range selection switch detent spring has gone too weak to latch. Any suggestion as the manufacturer of said switches please? I seem to recall using these switches back in the 70’s but can I remember the maker’s name?


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