Geo wrote:
On Sun, 13 Aug 2017 19:15:52 +0000 (UTC), bob prohaska
wrote:


Sorry, it's a reliance electric 701819-X . Web searches find it for sale,

It is a full bridge rectifier but two arms of the bridge use SCRs
instead of diodes. Their gates are controlled (via the G1 and G2
terminals) to switch on for a variable portion of a cycle thus varying
the power transferred.

Ok, now the fog is lifting, slightly 8-)

Many thanks for reading and replying!

bob prohaska


A Solartron variable bench power supply of that vintage used the
technique to reduce the input to the linear regulator when then output
voltage was dialled low and the 5 Amps would have resulted in too high
a dissipation in the regulator transistors.