[John L Stewart]

The Schema for this on was much faded, so it is redone here.

A 2.5 KV, 0.5 Amp Constant Current Power Supply

This power supply was used to drive a He-Ne Laser built by Eric Rawson from scratch at the U of T physics lab in 1965. I recall Eric cutting the optical flats on a drill press in the lab. He did all the glassware & got his laser going. The research got him a PhD in Physics. Not sure where Eric went, but seems to me most of us ended up getting very good jobs.

I got to do this brute force supply for the project. The passer is a parallel set of three 813’s. For this application it seems a simple cct was OK for the requirement. So no separate error amp beyond the pentode connected 813s & an 0D3/VR150 stabilized grid supply.

All the iron was supplied by Hammond, they were very good at specials. I had noticed in earlier work that the primary turn-on surge was sufficient to weld the turn on relay contacts closed, a dangerous situation. On one project I measured 450 Amps while connecting to a 240 volt supply. So the primary on this PS has a stepped turn on, first thru a total of 4R for about 5 cycles of the supply waveform & then direct. That is done by a pair of DPST relays having large contacts.

Filaments of the three 813s are supplied by three separate 10 volt, 5 amps windings on another transformer.

The AC to DC is done by a full bridge of 12 Philips PH103 silicon diodes, rated at 2KV each. All these are in parallel with a set of twelve 470K, 2W equalization resistors. The filter cap is 4 microF, 4KV oil filled.

Small resistors at the sockets are in each screen & grid lead to swamp any tendency to parasitic oscillation.