[GreenKeys] Model 19 parts and questions

[wa2hwj at att.net]

The rectifiers supplied with the Model 19 can be used for a "local loop".
They also supply power to the keyboard punch and bias
voltage current to the line relay. The line relay is wired to use the power
supply to then key an internal loop for the printer.
The actual signal "loop" is provided externally in a
standard configuration. If the wiring is "stock" then there should
be a connection at the polar relay's contacts that can be shorted, thus 
creating the "local loop". If the polar relay is removed, the socket
contacts for the relay's common and MARK/SPACE contacts can be
jumpered out. (This holds true for any "stock" TTY, by the way.)
In fact, if a milliameter is placed in the correct contact positions, the machine
should lock up and the loop current can be read. 
I would caution that the supply be tested for
good DC since the rectifier and caps are pretty old. Ripple on the DC would definitely
impact the performance of the mahcine if the supply is used to provide
the loop voltage. 
Wiring diagrams for the Model 19 are in the "New RTTY Handbook" by
Byron Kretzman and the TAB "RTTY Handbook" by Wayne Green.

73,
Jack K0TTY

NNNN

-------------- Original message from WA5CAB at cs.com: -------------- 


> Kevin, 
> 
> It's been far too many years since I last played with an M15 or M19 to answer 
> most of your questions so you'll have to wait for someone with more recent 
> experience to speak up. But I can answer your questions about the RA-87. Yes, 
> it is the DC loop supply. And although odds are that you need to add at least 
> one jumper to close the loop for the printer and probably some others to put 
> the keyboard in series with the line printer (as the machine would normally 
> have been connected into external circuits), odds are also that the RA-87 isn't 
> working. 
> 
> First, it has filter capacitors that may need to be replaced (not really a 
> big deal other than finding something that fits mechanically). Second, it uses 
> a selenium rectifier and odds are almost 100% that it is bad. Selenium rectifiers turned out to have a 30-50 year shelf and service life (fact not 
> known 
> when they were new). So it needs to be replaced with a silicon rectifier. 
> Until that is done, I would unplug the AC cord for the RA-87. 
> 
> Also, if the 19 set has a rectifier with an RA-87 or RA-87-A nameplate, it's 
> may be a military set. Look around for a nameplate or nameplates for the set 
> or the other components. Something beginning with TT, TG or AN/FGC for 
> example. If you can locate anything like that, it's possible one of us may have 
> the 
> TM 11 on that particular set. 
> 
> In a message dated 8/22/2008 11:12:19 AM Central Daylight Time, 
> kh-phillips at 9-5usa.org writes: 
> > First for the parts, I need the cord that pulls the carriage back on the 
> > return. The second part I need is, I think, one of the Y-levers. It is 
> > the longest one. I hate to admit it but in my ham-fisted attempts to 
> > get the thing running I got the carriage off track and ended up with the 
> > couple of broken parts (that I know of). 
> > 
> > The set has been sitting unused for 35-40 years in a house which had 
> > been closed up but still had utilities connected and running. The man 
> > who sold it really thought it would still be in operating condition. 
> > The AC has been kept on in the house but this was in south Louisiana so 
> > the humidity level, even with AC, is much higher than anyplace else! 
> > The set has a Signal Corps RA-87 Rectifier. I had to replace the DC 
> > cord. The machine runs but is running open. The bars under the 
> > carriage just vibrate back and forth. (I'm new to teletype so I'm not 
> > familiar, yet, with a lot of the terms.) The tape punch works fine but 
> > the keys on the carriage do not operate whenever a key is pressed on the 
> > keyboard. 
> > 
> > One question I have is whether or not the 60ma loop is being supplied by 
> > the RA-87? Second question is, assuming the loop is supplied by the 
> > RA-87, what/where should I check to get the thing to run closed? 
> > 
> > One DC socket on the power supply has apparently gone dead. The other 
> > is still active but the plug doesn't fit well at all. I'm tracking down 
> > some schematics and may try to have the PS rebuilt. 
> > 
> 
> Robert & Susan Downs - Houston 
> wa5cab dot com (Web Store) 
> MVPA 9480 
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