My latest toy arrived on Monday, a TDMS5BV telegraph distortion measuring set (TDMS). This guy (hopefully!) can generate a test pattern and all sorts of other magic to help test circuits (not particularly relevant) and also teleprinters (definitely relevant).

It tests polar relays too, thus the socket on the front. I have a PDF of the manual and schematic for it. I now also have a variac so I carefully brought the TDMS up to voltage while watching the current and all seemed well – no exploding electrolytic. But it did nothing. After bothering to read the manual it gave instructions on how to prepare the instrument. After a fiddle with a control at the back it produced the required circular(-ish!) trace and the polar relay started to cycle. So far, so good…