"Jim Lesurf" wrote in

During the first years of manufacture the ampliers/recievers in the
Armstrong 600 range used a thermal delay relay to avoid a surge when the
unit was switched on.


I remember it well as I had a 600 with one in. To me it appeared to be a
cheap & nasty little thing that failed very early on. I simply shorted it
out and the receiver continued to work for many years without it.

These were expensive.

Maybe, but it was still cheap & nasty.

And they were one of the main failure modes which
brought sets back for repair. One of the reasons I avoid physical relays.

But a thermal relay is a totally different animal from a conventional
electromagnetic relay. They have very slow make & break of the contacts, and
the characteristics of the bi-metal strip changes with age. Having said that
I've known *much* better and more reliable thermal relays than the one you
used.

I replaced them in later sets with a better PSU that simply didn't need a
mechanical relay.

Your original PSU didn't need it either IME. :-)

David.