[GreenKeys] Trepac 538-A Telegraph Relay For Sale

[Joe Clanin]

If anyone does happen to be interested, it'll come with the socket /
bracket to mount it to a 15/19/etc. Picture attached.

-Joe




On Sun, Jul 19, 2020 at 9:33 AM Jim Haynes <jhhaynes at earthlink.net> wrote:

> Oh, that takes me back.  (Not that I want it, but it takes me back)
> to 1958 when I first had a summer job at Teletype.  My boss had a
> number of little projects that a summer student could work on, and one
> he handed me was to do a solid state line relay.  He had one, I think
> it was Trepac but maybe a different model, that had been taken apart
> to see how it worked.  At the time there were not many high voltage
> transistors, so the relay used two of them in series with suitable
> monkey business to get them to turn on and off together.
>
> I couldn't think of much of anything to do along that line, but had
> a different idea.  At the time there were power transistors for auto
> radios, so I said why don't we wind the selector coils for 12 volts,
> 600 ma and use a power transistor to drive them.  So I got some coils
> made and tested it - also turns out my boss had already thought of that.
> So it didn't solve the line relay problem, but the idea did take hold
> by the time of the Model 32/33/35 and later equipment.  Whomever
> designed the selector magnet driver didn't like my simple saturated
> transistor model and changed to a constant-current driver, which probably
> did give faster operation as needed for 110 baud.  Also unknown to me
> there was a transistor driver developed for 60ma selectors, as well as
> a vacuum tube driver somewhere back in the woods.
>
> The sad part of this is that I failed to sell what I still consider a
> better concept.  That was to have every selector magnet equipped with
> a transistor driver, and every transmitting contact equipped with a low
> voltage circuit, and run the whole set internally on low voltage along
> the lines of RS-232 polar signals.  (RS-232 didn't come along until
> several years later, and for a different purpose)  This would get rid
> of all the current loops inside the set and greatly simplify the
> internal switching.  No more having to open a loop to insert something
> and keep the loop closed when something was not in use.  And would easily
> accomodate other transistorized accessories such as a regenerative
> repeater.  The interface between the set internals and the outside world
> could be a line relay, or an electronic line relay, or the output of a
> modem, or anything else you might happen to want.  But for some reason,
> I'm guessing the old geezers at Bell Labs, the Teletype selector magnet
> drivers were designed to be in current loops, even though it was at low
> voltage.
>
> Jim W6JVE
>
>         ---
>
>         "Ya can argue all ya wanna, but it's dif'rent than it was."
>         "No it ain't! No it ain't!  But ya gotta know the territory."
>                 Meredith Willson, The Music Man
>
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