[GreenKeys] Of current loops and voltages.. (M15 20mA / 60mA)

Wed Sep 16 00:15:44 EDT 2015

Our friend Lee wrote:

"For some time now I have been wondering why so many postings have included
"features" that I had never encountered back in the 70's when I was very
active on RTTY.   I finally realized that machines, while not as "scarce"
as they had once been, were still not "plentiful" and therefore most
machines had been "stripped" of a lot of the original wiring and were
almost always used for two way radio communication.   Indeed, in most cases
you could safely assume that the magnets, keyboard and terminal unit were
always operated as a "closed loop."

Yes, it was absolutely SOP to have the "typing unit" echo the keyboard.
But what you might encounter today?   Who knows.

73

Lee  K9WRU"

Yeah, it's almost seeming like I got "lucky" with my machine, in that it
appears to be almost totally original, in terms of the wiring layout. And
it's all in very nice shape, to boot - I wouldn't dream of ripping it out
with the aim of 'simplifying" matters.

My guess is that a well-placed jumper will put the KB / TU in series, and
give a local echo of the transmission. But that dang terminal block - why
so many terminals when we 'only' need two each for KB and TU? And while
some of the terms are un-wired, many are - so Teletype Co obviously had
something in mind for all that crap! ;-)

So my machine has KB on #32 & #34 - and TU on #45 & #46. Of the top of
anyone's head, where should the 'local echo' jumper go?

On Tue, Sep 15, 2015 at 11:49 PM, Lee Mushel <herbert3 at centurytel.net>
wrote:

> For some time now I have been wondering why so many postings have included
> "features" that I had never encountered back in the 70's when I was very
> active on RTTY.   I finally realized that machines, while not as "scarce"
> as they had once been, were still not "plentiful" and therefore most
> machines had been "stripped" of a lot of the original wiring and were
> almost always used for two way radio communication.   Indeed, in most cases
> you could safely assume that the magnets, keyboard and terminal unit were
> always operated as a "closed loop."
>
> Yes, it was absolutely SOP to have the "typing unit" echo the keyboard.
> But what you might encounter today?   Who knows.
>
> 73
>
> Lee  K9WRU
>
> ----- Original Message -----
> *From:* drlegendre . <drlegendre at gmail.com>
> *To:* Chris Elmquist <chrise at pobox.com>
> *Cc:* Green Keys <GreenKeys at mailman.qth.net>
> *Sent:* Tuesday, September 15, 2015 9:32 PM
> *Subject:* Re: [GreenKeys] Of current loops and voltages.. (M15 20mA /
> 60mA)
>
> Gents,
>
> As ever, thanks so much for all of your input.. With all the willing
> helpers, the info flows quickly.. ;-)
>
> For now, suffice to say I've got the whole 20mA / 60mA and 120V / 24V
> thing nailed - as pertains to both early (M14, M15, etc) and later (M33,
> etc). We're all good, far as I can tell.
>
> But there are still a couple of questions: Were machines like the M15
> normally wired in a "local echo" config? I mean to say, was it SOP to copy
> the output of the keyboard to the typing unit as its sent down the line -
> or was the sending operator normally typing 'blind'?
>
> This would obviously involve placing the KB and TU in series with the
> circuit, and no such connection is shown in the doc(s) I'm using. I did see
> a doc that showed what looks like a jumper between one KB and one TU pin
> each.. is this is the local echo connection? It seems difficult to type
> when there's no feedback on the "screen".
>
> Other question - how is the Send / Rec / Break device used? Break seems
> obvious - you press down on the 'small' switch paddle, which open-circuits
> the KB line. If the KB were in series with a selector coil, it would cause
> the coil to let go and the machine to start printing continuous NULLs. It's
> the same situation as with old-school telegraph - you open aka space
> ("BREAK") the line to interrupt the other party to get their attention.
> This is clear..
>
> But how is the 'large' switch paddle used? How does it control Send &
> Rec?  I can't seem to make it do anything..
>
>
>
> On Tue, Sep 15, 2015 at 1:38 PM, Chris Elmquist <chrise at pobox.com> wrote:
>
>> On Tuesday (09/15/2015 at 04:16PM +0000), paul0926 at comcast.net wrote:
>> >    For me this list is fine. It works like every email list in every
>> >    company I work for and with. It is expected that a person does a
>> reply
>> >    to all unless they specifically intent to cut people out of the
>> >    conversation.
>>
>> Boy, yes.  Agreed.  Reply only to the original poster.  Reply-All to
>> the group.
>>
>> Chris NØJCF
>>
>> >      ------ Original Message ------
>> >      From: Jim Walls
>> >      To: Greenkeys
>> >      Sent: September 15, 2015 at 10:05 AM
>> >      Subject: Re: [GreenKeys] Of current loops and voltages.. (M15 20mA
>> /
>> >      60mA)
>> >
>> >    Bill drlegendre at ... wrote (in part):
>> >
>> >    > A couple other members wrote me (off list, not sure why)
>> >
>> >
>> >
>> >    The why is because this list is setup so that replies go to the
>> >    original poster and not back to the list.  In my opinion, this is a
>> >    really poor way to set up a mailing list for exactly the reason you
>> >    saw.  Lots of people reply giving the same information (hopefully)
>> >    rather than the first person who responds is seen by all and everyone
>> >    realizes that there is no need to reply - again.
>> >
>> >
>> >
>> >    Jim - K6CCC
>>
>> --
>> Chris Elmquist
>>
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>
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