Previous message: KIM Uno /PiDP-11 plans...

Noel Chiappa jnc at
Fri Oct 23 09:57:23 CDT 2015

    > From: Dave Wade

    > What I found hard was obtaining centre off switches as it appear from
    > this picture ... that PDP-11 Switches may be flipped up or down, or is
    > that not true?

No, they are all 'standard' (except for the mounting) SPST switches; most
(e.g. the address/data bits) are normal two-position, although some (LOAD
ADDR, DEPOSIT, EXAM, START and CONTINUE, IIRC) are momentary-contact. The
'toggle' (the plastic part that fits over the switch) has an off-center shaft
that goes around the switch's metal actuating shaft, so that the toggle can be
level when the switch is in the 'un-set' position.

Some of the switches are installed 'the other way around', and they depress
instead of lift (typically the address-data switches lift, and the function
ones depress, although there are exceptions - e.g. DEPOSIT is a lift).

    > I believe they were made by C&K who are still in business. I wonder if
    > it is worth approaching them.

If they're not actually still availble - see below.

    > The double pole version appears to be still "stocked", I see Farnell
    > has some in the UK

That is _almost_ the exact switch (I just about had a heart attack when I saw
them, and started to order some until I realized they weren't quite it); it
has the right mounting mechanicals (note the two triangular side plates with
the holes through the tips - the toggle have pins which go into the holes,
and the toggle pivots on them).

Alas, it's DPDT, not SPST. And it's momentary contact (although each PDP-11
panel does contain some momentary-contact switches).

But if C+K is still making _these_, they should have no problems making the
SPST version - if, in fact, they are not still in production.

I tried looking through the catalog at that site, to see if I could find the
SPST version, but no luck. (Although maybe I'm just a klutz about that site -
it wasn't easy for me to use.) Maybe your parts-search-fu is better than mine?


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