[GreenKeys] A little help

[Duncan Brown]

Mine did not have a bias control or a shift (gain?) control. Only had a 
Normal/Reverse switch and NE-2 bulbs for Mark & Space.  It did include 
the loop supply, but the limiting resistor was external and a short in 
the line burnt out the transformer!

Duncan

On 9/16/2019 11:02, Duncan Brown wrote:
> Tom,
>
> I built a "filterless" TU once. It had 4 tubes (no OA2) and might have 
> been similar. I think there were three dual triodes and a power tube 
> to drive the loop.  The principle was to send the audio tones through 
> a limiter and then through a small value (high reactance at audio) 
> capacitor - maybe about 150 pf (?).  The two tones will come out at 
> different levels due to the reactance of the capacitor. The two audio 
> levels are detected and then amplified to drive the loop.
>
> Worked well with strong signals without QRM. Seems like it didn't have 
> enough gain for 170 hz shift, but this was back around 1968. I'll look 
> around to see if I have any documentation on it.
>
> Have fun,
>
> Duncan
> K2OEQ
>
> On 9/16/2019 10:22, til128 at juno.com wrote:
>> Hi all:
>> I am looking for some help in identifying a TU that I recently acquired
>> with no paperwork. :-(
>> It was built by Jack K2TTY Hart. (SK)
>> It is labeled "Filterless TU"
>> It has a Bias adjustment and a knob on the front labeled "shift".
>> There is a loop circuit at 135v at 60 mA.
>> There are 5 tubes. See layout attached.
>> I have tried with multiple tones to no avail.
>> I have searched RTTY magazine.
>> My worst fear is that it wasn't completed as the 12AT7 (center)
>> and the 12BH7 (Bottom ctr) tubes are not getting warm.
>> It is a very well built item and I would love to use it.
>> Thanks for your kind attention and help identifying this.
>> BTW - bottom left tube is "OA2"
>> Tom WB2TTY Tillson
>> ITTY Listening:
>> ITTY:   HTTP://INTERNET-TTY.NET:8000/ITTY
>> AUTO:   HTTP://INTERNET-TTY.NET:8030/AUTOSTART
>> GREENWICH: HTTP://INTERNET-TTY.NET:8040/EUROPE 
>> <http://internet-tty.net:8040/EUROPE>
>>
>>
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