[GreenKeys] Teletype Corp. machine with a tube (was acrylic case)

[Bruce Gentry]

I think you will find the 35L6 controls current in a shunt field. The 
motor may be compound wound so it will start promptly and avoid 
overspeeding. The effects of fields are cumulative, not just the 
strongest one taking control. Without seeing the motor circuit diagram I 
can't make any further speculation. The 25/35/50L6 tubes have rather 
large cathodes and will work surprisingly well at lower filament 
voltages. They also perform unexpectedly well on lower plate voltages, 
like 28 volts. The most extreme example of low voltage operation I have 
encountered was on a friend's older Beechcraft Bonanza airplane. A 28D7 
was used in the propeller governor circuit with 12 volts on the filament 
and plate.

       Bruce Gentry, KA2IVY


On 2/2/19 10:49 AM, Duncan Brown wrote:
> Nick,
>
> Teletype Corp did make a machine with an electron tube in it: the 
> Model 31 (AKA TT-30/AGA-1) that ran on 28VDC. A 35L6GT was used to 
> switch a resistor into the motor circuit of the series governed DC 
> motor for speed control. It was a KTP machine that was designed for 
> use with RTTY/RATT. They were apparently afraid the normal open 
> contacts in the speed control would produce too much RFI. Although 
> running on 28VDC, the 35L6GT apparently had enough gain with 28 VDC on 
> the filaments and would probably last a bit longer.
>
> The first time I powered up the Museum's unit, it seemed to run OK for 
> a few seconds, but then it slowed down. I quickly killed the power and 
> checked  the unit for something binding or a bad bearing. Everything 
> seemed OK, so I powered it up and it did the same thing: slowed down 
> after a few seconds. Then it ran fine and I suddenly realized that you 
> had to wait for the tube to warm-up before the speed control took effect!
>
> There is also a 250VDC generator connected to the TTY's motor to 
> provide voltage for the loop and the FSK converter. So the TT-30, 
> besides being the only TTY with a tube, is also the only  TTY with a 
> dynamotor!
>
> Have fun,
>
> Duncan
> K2OEQ
>
> On 2/1/2019 20:29, Nick wrote:
>>
>> And the vacuum tube you can see on the lower right side above the 
>> switch inside the case is just a little steampunk add-on. The tub 
>> actually works, it is a Dekatron counting tub, spinning around to an 
>> adjustable speed. At our event last weekend, I pulled somebody's leg 
>> and said: "this is a super rare tube driven teletype machine, 
>> probably the only one on the planet" - but the guy figured it out 
>> pretty quickly and we both laughed.
>>
>> Enjoy the pics - any improvement ideas are always welcome.
>>
>> 73
>>
>> Nick  -  N0NCQ
>>
>
>
>
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