[GreenKeys] M15 with Polar Relay -- Configuration

Thu Jan 28 08:49:53 EST 2021

A side observation, if this machine came through MARS channels, you may find Army or Navy manuals useful.  I think TM11-2xxx numbers would be where you'd find Army versions.  TG7 was one of the designation for the M15.  Some of the Teletype bulletins do address military variants.

John, W9DDD

> On Jan 28, 2021, at 6:39 AM, Paul Birkel <pbirkel at gmail.com> wrote:
> 
> I see that http://www.k7tty.com/development/teletype/model-15/index.html has useful material, including the following claim:
>  
> “If a polar relay has been installed, it is necessary to connect one of the coil lead from the selector magnet which was connected to terminal 65 and move it to terminal 66. This lead goes to terminal 42. Next remove the lead which goes to the polar relay socket from terminal 61, and tape up. Then move the other selector magnet lead which was on terminal 62 and connect it to terminal 61 which goes to terminal 41.”
>  
> However that page also includes a labelled photo indicating a big-button switch front-n-center identified as “POLAR NEUTRAL KEY”, which I do have.  Perhaps The Teletype Corporation has “already thought of everything” :->.  Note that it’s located on the Keyboard subunit, not the Base – which seems like an odd placement to me in terms of functional allocation.  It’s more clearly visible in Figures 19 and 22 of tm11-2215-teletypewriter-tt5-model-15-20pct-of600dpi-main.pdf.
>  
> I think that I have either a Base A or Base B, but haven’t yet confirmed which.  Those directions appear to apply in either case, but presumably only when one is operating a printer-only unit.
>  
> Nick England and Jim Haynes both point out that I could simply bias the existing polar relay properly.  Figure 45 (page 41) of tm11-2215-teletypewriter-tt5-model-15-20pct-of600dpi-main.pdf documents exactly this implementation in the lower-left along with Note 1 “Polar Neutral Key in Neutral Position”.  The bias winding is fed in series with a pair of 2K ohm resistors from the nominal 110 VDC line.  If I understand the wiring of the table correctly then the same supply can be used to bias the polar relay *and* supply the loop.  While I do have the table and a REC-11 I’m missing this intermediate wiring (“Electrical Service Assembly”).  Having the pair of “Test Jacks” to establish a local loop would be quite handy.
>  
> Figure 56 (page 51) illustrates a pair of interconnected teletypewriters, making clear the role of this key/switch in the end-to-end circuit.
>  
> The Polar-Neutral Key is described in Section 111 (pp 141-143).
>  
> Like all Teletype equipment there are a bevy of possible configurations and employments of the M15; all left to the interpretation and eventual understanding of the “discerning installer” :->.  Endlessly fascinating.
>  
> Hopefully this note will help the next guy get started :->.
>  
> From: hwhall at compuserve.com [mailto:hwhall at compuserve.com] 
> Sent: Wednesday, January 27, 2021 6:16 AM
> To: pbirkel at gmail.com; greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] M15 with Polar Relay -- Configuration
>  
> Sounds as though you think you must drive your machine with a polar circuit because your machine is equipped with a polar relay. Is that right?
>  
> My previous Model 15 which I ran for years had a polar relay installed but I simply never used it & drove the machine via a 60ma local loop to the selector magnets.  If I recall correctly, the terminal block has enough connections there to allow one to reconfigure the machine to use or not use the polar relay (and other features).
> 
> Wayne
> WB4OGM
> 
> -----Original Message-----
> From: Paul Birkel <pbirkel at gmail.com>
> To: greenkeys at mailman.qth.net
> Sent: Wed, Jan 27, 2021 3:54 am
> Subject: [GreenKeys] M15 with Polar Relay -- Configuration
> 
> Good morning all;
>  
> I seek some guidance/experience with setting up an M15 that came equipped with a polar relay and otherwise essentially  “factory fresh” wiring harness.  My basic question is whether I can swap the relay for a non-polar one and then use the M15 “conventionally” … and if so, what would be the substitute relay?  And then … does anyone have such a substitute available for employment in this endeavor :->?
>  
> Alternatively, I do have another polar relay and definitely have more than a “passing interest” in leaving the M15 as received and instead setting up a local polar circuit to drive it that would in turn be patched into a normal local loop.  There’s not been much discussion of practical setup/employment of polar circuits here AFAIK; I enjoyed reading the AT&T Long Lines book on “Principles of Electricity” back in 2019 and intend to refer to it again before I proceed.
>  
> I originally received the M15 from an ex-MARS guy who eventually used it as an office printer with an early microcomputer system before putting it into storage a few decades ago.  He kept it well lubricated, thank goodness.  It appears to be configured using a standard 60 mA pulling magnet (no S/P switch nor a 3-position terminal block; the rangefinder does NOT have an HM marking; and the magnet definitely has round windings).  I haven’t yet checked the resistance on the loop to be triply sure.
>  
> My main terminal block appears to be physically different from that shown at http://www.baudot.net/gil/tty-machines/pics/M15-KSR-Gil-Iface-Terminals.jpg  I don’t know whether that’s significant.  It appears to be configured to separate the KBD from the PTR circuits.  The M15 wiring appears to be entirely original excepting one modification at the polar relay – which is a coaxial-cable stub (clipped off after ~2” and left hanging) attached to the rearmost pair of polar relay terminals that appear to have been otherwise unused (but can’t quite be sure of that, although there are no telltale snips that I can spot).  Possibly that’s a remnant of the earlier MARS use, and the separated KBD/PTR circuits reflect the later office-printer use.
>  
> Possibly the use a M15-polar configuration is documented in some RTTY publication?  At the moment I’m using the “New RTTY Handbook” as my starting point, but I imagine that there are other specific how-to articles …
>  
> Your various and sundry thoughts and observations will be much appreciated, thank you.
>  
> Good Health to You and Yours,
> paul
>  
>  
>  
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