[GreenKeys] Jack Selection for TTY equipment

[Christian Gauger-Cosgrove]

On 17 November 2013 18:38, Steve Ripper <steve.ripper at gmail.com> wrote:
> Switchcraft MT334BX at onlinecomponents.com only $6.87 each and 497 in
> stock.
>
Actually, if you go by the diagrams for the SB-1203/UG patch panel on
Nick England's (K4NYW) webpage the best jacks to use -- from
Switchcraft -- to replicate a patch panel like the SB-6/GG,
SB-1203/UG, SB-1210/UGQ, et cetera; but not the big fixed installation
patch panels (which are different, naturally) would be the special
order 2-conductor MT332C (WECo 303A-alike) and CMT336E (WECo
438C-alike) jacks.

The MT334BX (WECo 239AM-alike) is a three-conductor jack, with
normally closed tip and ring circuits. If one wanted to make the SET
jacks out of three-conductor jacks, I'd suggest the -- again, special
order -- CMT358 (WECo 290C-alike jack; if only because along with the
NC tip-and-ring conductors, it has two NO switch pairs. Which would be
good to have, since the SET jacks on the TTY patch panels are designed
that when you insert a plug into it, the equipment attached to the SET
jack is taken out of the loop, but the loop is still left continuous,
so if you have something patched into one of the LPG (looping) jacks
and decide to pull the normal equipment out of the circuit, the other
piece of equipment remains functional (and the loop doesn't start to
run open). For three-conductor looping jacks... you could also
probably use the CMT358, though wired differently. (Rewiring it so
that when the jack has nothing plugged in, the loop is bridged around
it, and when something is plugged in, the loop is run through it. As
opposed to the set jack which is loop bridged and set only to jack
when something is plugged in, loop run through the set when
unplugged.)

For the MISC jacks if you wanted three conductor, you could get away
with an MT334BX. With the NC contacts connected together.

In any case, the proper way to use the switchboard would be plug the
first end of the patch cord into the SET or MISC jack, and then plug
it into a LPG jack, lest you open a loop and put loop-current on the
free end of a patch cord.


Hope that was informative, even if it comes from a definitive
NON-EXPERT in the subject.

Cheers,
Christian


-- 
Christian M. Gauger-Cosgrove
STCKON08DS0
Contact information available upon request.