[GreenKeys] Kleinschmidt TT-4

[Duncan Brown]

On 3/30/2026 9:57 PM, David S via GreenKeys wrote:
>
> Any tips on getting this TT-4 connected and running?
>
>
> I am not there yet, but I have the deramp interface board adapted to 
> the Model 28, would this be appropriate to drive this TTY, or is it 
> expecting more of the current loop signal a model 15 would be 
> getting?  I have an iRL FSK-1000, but it wont drive the Model 28s, 
> either it isnt working or I am doing something wrong.  Ran though the 
> manual on the iRL a couple of times and haven't cracked that code yet.
>
> The only references I see is a handful of youtube vids from gregga1973 
> and Marks tech channel, not nearly as extensive a reference set as the 
> Model 28.
>
> Looking forward to not only getting this TT-4 running, but on the air
>

David,

The TT-4 is a good solid machine to start out with. Nothing fancy, just 
a basic machine and one where you can see most of what is happening. It 
is a good choice for use in a military vehicle. It was used in early 
versions of the AN/GRC-26 and in some versions of  the AN/GRC-142.  It's 
big brother, the TT-98, was used in later versions of the AN/GRC-26, the 
AN/GRC-46 and AN/GRC-142.  (I don't know how a M28 would hold up in a 
mobile environment.)

If you are not familiar with the US Army military RATT (RTTY) rigs of 
the 1950-80s, see RATTRIG.COM  (they also have pdfs of most of the manuals.)

I'm not familiar with "deramp",  but the TT-4, M15 and M28 all require a 
20 or 60 ma. current loop at about 120VDC, and should interface the 
same.  ( If the M28 has a polar relay on the line, it is polarity 
sensitive and may be why the FSK-1000 doesn't work.) The TT-4 has a 
switch on the side near the selector magnet to select either 20 or 60 
ma. loop.  The FSK-1000 can supply the loop and should work fine with 
the TT-4.  If the dramp works with the M28, it should work with the TT-4.

The TT-4 has the advantage of a built-in adjustable loop resistance and 
current meter (it may be the only one).  If the meter reads backwards, 
just reverse the loop connections to the TT-4.  The TT-4 selector magnet 
is not polarity sensitive.

The first thing to do on any new TTY is to try to turn the motor by hand 
(CW for the TT-4).  It should turn without too much resistance.  Second, 
connect the loop and adjust for 20 or 60 ma. (with the loop current 
switch in the corresponding position).  Then, hit the "Y" key and turn 
the motor by hand.  You will see the ma. meter drop and then see the 
current come and go as the signal is encoded. Continue turning the motor 
by hand and the "Y" type arm should come up and then the type basket 
will move to the next position.  The type arm may not come up all the 
way due to lack of inertia when turning the motor by hand.

The third step is to plug in the motor. But before you do, a WARNING: 
ground the chassis with either a ground strap or a grounding power 
cord.  The series-governed motor can generate a lot of RFI, so they put 
a big RFI filter in the base.  This filter includes capacitors from both 
sides of the AC line to chassis.  So, without a ground, the chassis will 
be 60 Volts above ground.
Plug it in and turn on the motor and start typing!  (See the manual for 
adjusting the Bias & Range controls.)


Hope this helps!

Good luck & have fun,

Duncan Brown, K2OEQ
USASA    31J30

Antique Wireless Association
  Communication Technologies Museum
    Asst. Curator, Commercial Equipment
(also chief TTY op & repairman)

i-Telex: 212503

www.antiquewireless.org

AWA Youtube channel: 
https://www.youtube.com/channel/UCX55peBhzeX1qps_VYXdLBA

Virtual AWA Museum TTY Tour: https://www.youtube.com/watch?v=TpB6jM90VV8