[GreenKeys] Flesher TU-170 Loop Key Transistor

[John, W9DDD]

Now that I'm a little more awake, I now remember that the internal loop 
supply is about 80 VDC.  It requires "stereo" plug where the selector 
magnets are on Tip and Ring.  The sleeve is ground and in my case I use 
that as the shield that happened to be in the cable.

There is no internal snubber circuit, but with the lower voltage perhaps 
not a problem. I vaguely recall that the "kick" would be 2x the supply 
voltage.  (Hey it's been 50 years since I graduated, and that's theory 
I've not used in a while)

When I first got mine, I wondered where the 2k resistor is. There isn't 
one.  You'll notice there's 2 resistors in the emitter circuit.  This is 
a current regulator circuit. For mark condition, the base is switched to 
the +12 volt supply rail.  As the loop current rises to 60mA, the 
voltage drop across the emitter resistors increases toward 12 volts.  
Somewhere around 11.4 volts across the emitter resistors the MJE340 
starts to regulate the current to 60mA.  So the MJE340 is dissipating 
about 4.5 watts in the mark condition.


John, W9DDD

On 10/31/2020 12:22 AM, Harold Hallikainen wrote:
> Did not realize there was an internal loop supply! Missed that as I was
> reviewing the manual. I am temped to put a clamping zener across the
> printer connection to the TU-170.
>
> Thanks!
>
> Harold
>
>> I see you mention the 152590 loop supply, you realize that the TU-170 has
>> an internal loop supply?
>>
>> I'd better shut up, half asleep and making mistakes.
>>
>> John, W9DDD
>>
>>
>>> On Oct 30, 2020, at 11:02 PM, hwhall at compuserve.com wrote:
>>>
>>> I've built keyers using that transistor and always had an RC snubber
>>> across them.
>>>
>>> Wayne
>>> WB4OGM
>>>
>>> -----Original Message-----
>>> From: Harold Hallikainen <harold at mai.hallikainen.org>
>>> To: Green Keys <greenkeys at mailman.qth.net>
>>> Sent: Fri, Oct 30, 2020 8:20 pm
>>> Subject: [GreenKeys] Flesher TU-170 Loop Key Transistor
>>>
>>>
>>> I'm looking at the manual for the TU-170 and see that it keys the loop
>>> with an MJE340 which has a maximum Vce of 300 V. 152950 loop supply has
>>> a
>>> loaded output voltage of 125 V. Can the MJE340 take the inductive spike
>>> when it opens the loop, or should a clamp be added?
>>>
>>> Thanks!
>>>
>>> Harold
>>>
>>>
>>>
>>> --
>>> FCC Rules Updated Daily at http://www.hallikainen.com
>>> Not sent from an iPhone.
>>>
>>>
>>>
>>> --
>>> http://w6iwi.org
>>> ______________________________________________________________
>>> GreenKeys mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:GreenKeys at mailman.qth.net
>>>
>>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>> https://teletype.net/gksearch
>>>>>> 2002-to-present greenkeys archive:
>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>>> 1998-to-2001 greenkeys archive:
>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>> http://comcents.com/tty/greenkeyssearch.html
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to hwhall at compuserve.com
>>> ______________________________________________________________
>>> GreenKeys mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:GreenKeys at mailman.qth.net
>>>
>>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>>> https://teletype.net/gksearch
>>>>>> 2002-to-present greenkeys archive:
>>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>>> 1998-to-2001 greenkeys archive:
>>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>>> http://comcents.com/tty/greenkeyssearch.html
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to w9ddd at tapr.org
>> ______________________________________________________________
>> GreenKeys mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:GreenKeys at mailman.qth.net
>>
>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>> https://teletype.net/gksearch
>>>>> 2002-to-present greenkeys archive:
>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>> 1998-to-2001 greenkeys archive:
>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>> http://comcents.com/tty/greenkeyssearch.html
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to harold at w6iwi.org
>