[GreenKeys] Model 14 keyboard adjustment

Harold Hallikainen harold at w6iwi.org
Sun Aug 6 23:38:50 EDT 2023 

Dry contacts are rough! I worked on a project for movie theaters where the
private key was held in RAM backed up by a lithium cell. The cell was
nickel plated as were the contacts on the battery holder. The RAM and
clock and security circuits drew 13 uA from the cell when main power was
off. We had problems with contact fritting resulting in a high resistance
contact between the cell and the holder causing the private key to be
lost. We finally had to solder in the cell. A lot of switches have minimum
current contact ratings for this reason.

Harold
https://w6iwi.org


On Sun, August 6, 2023 7:21 pm, John, W9DDD wrote:
> And when Bell started putting TWX modems on the side of 28KSRs, they had
> to put gold plate on the keyboard contacts due to the lower voltages
> used in the 101 series modems..
>
> ---
> ----
> You said "tomorrow" yesterday.
>
> The above comments or recommendations are SWAG. Use at your own risk.
> John, W9DDD
>
> On 8/6/2023 5:29 PM, Gerry Block wrote:
>> ...and btw switches and relays for use in low level-low current use
>> are even today referred to as "dry circuit switches".  never thought
>> much about that term of art but it makes sense ...
>>
>> Sent from my iPhone
>>
>>> On Aug 6, 2023, at 3:18 PM, David V. Corbin
>>> <david.corbin at dynconcepts.com> wrote:
>>>
>>> 
>>> Gerry 😁😁😁
>>>
>>> I started in 72 formally but was exposed circa 68. Sent last summer
>>> restoring 2 of the 3 that I own (all model 33s)…getting rid of nests
>>> and webs is “fun”… eventually I would like to get back for the
>>> third
>>> as it is potentially the rarest- tractor feed for Western Union…
>>>
>>> Get Outlook for iOS <https://aka.ms/o0ukef>
>>> ------------------------------------------------------------------------
>>> *From:* Gerry Block <gblock at sbcglobal.net>
>>> *Sent:* Sunday, August 6, 2023 4:50:01 PM
>>> *To:* David V. Corbin <david.corbin at dynconcepts.com>
>>> *Cc:* Paul Heller <paul0926 at comcast.net>; Jeffrey Golas
>>> <jeffg at junknet.net>; Greenkeys <greenkeys at mailman.qth.net>
>>> *Subject:* Re: [GreenKeys] Model 14 keyboard adjustment
>>> it's fun beating a dead horse.
>>> i think everything everyone is saying is true.  earlier in this
>>> thread somebody used the magic term " compliance voltage" which is
>>> the key to driving the coil inductance. a constant current supply
>>> with a zero load (open) output voltage of 15v doesn't solve much.
>>> when i was running machines i used a 150v hp lab supply set to
>>> "constant current".  so the "compliance voltage" was 150v - until the
>>> load dynamically needed less to stay at 60ma.
>>> this is not much better than a REC loop supply with a wire wound
>>> resistor but is smaller and weighs less and generates little heat and
>>> impresses your neighbors.
>>>
>>> i apologize in advance. i was working these machines this when the
>>> machines were pretty new and had never seen a machine in storage for
>>> 50 years.
>>> i have kept only a model 12 and i swear i will lubricate it and get
>>> it working.  Btw i had a model 28asr that was NEW!
>>> enough. ...
>>>
>>>
>>>
>>> Sent from my iPhone
>>>
>>>> On Aug 6, 2023, at 1:23 PM, Gerry Block <gblock at sbcglobal.net> wrote:
>>>>
>>>> paul is absolutely correct.  the contacts are not designed for low
>>>> level switching.
>>>> if you use a normal loop your problems related to dirt and oil will
>>>> go away.
>>>> i didn't catch it - what device is this thing driving?
>>>>
>>>> Sent from my iPhone
>>>>
>>>>> On Aug 6, 2023, at 6:37 AM, David V. Corbin
>>>>> <david.corbin at dynconcepts.com> wrote:
>>>>>
>>>>> 
>>>>> Paul, trying to wrap my head around this. Ohms law. If the state is
>>>>> static, then to keep a 60mA flow, the voltage will be a constant
>>>>> based on the resistance of the loop. Now when the state transitions
>>>>> to “open” it does not matter how high the voltage goes, there
>>>>> will
>>>>> not be current. Now when the circuit initially closes, inductance
>>>>> May raise the voltage needed for achieving the target current, but
>>>>> then it will lower to the steady state value.
>>>>>
>>>>> This is why I use programmable current supplies rather than
>>>>> supplies where one sets the voltage.
>>>>>
>>>>> Get Outlook for iOS <https://aka.ms/o0ukef>
>>>>> ------------------------------------------------------------------------
>>>>> *From:* greenkeys-bounces at mailman.qth.net
>>>>> <greenkeys-bounces at mailman.qth.net> on behalf of Paul Heller
>>>>> <paul0926 at comcast.net>
>>>>> *Sent:* Sunday, August 6, 2023 9:30:50 AM
>>>>> *To:* Jeffrey Golas <jeffg at junknet.net>
>>>>> *Cc:* Gerry Block <gblock at sbcglobal.net>; Greenkeys
>>>>> <greenkeys at mailman.qth.net>
>>>>> *Subject:* Re: [GreenKeys] Model 14 keyboard adjustment
>>>>> I remember a discussion years ago where a number of folks said high
>>>>> voltage was important for the contacts. The design voltage was much
>>>>> higher than 15v. You might try a loop source that delivers higher
>>>>> voltage and 60ma. That might work better with your contacts.
>>>>>
>>>>> Paul
>>>>> W2TTY
>>>>>
>>>>> ITTY: HTTP://INTERNET-TTY.NET:8000/ITTY
>>>>> <HTTP://internet-tty.net:8000/ITTY>
>>>>> ITTY 100: HTTP://INTERNET-TTY.NET:8010/ITTY100
>>>>> AUTOSTART: HTTP://INTERNET-TTY.NET:8030/AUTOSTART
>>>>> <HTTP://internet-tty.net:8030/AUTOSTART>
>>>>> EUROPE: HTTP://INTERNET-TTY.NET:8040/EUROPE
>>>>> <HTTP://internet-tty.net:8040/EUROPE>
>>>>>
>>>>>> On Aug 6, 2023, at 7:27 AM, Jeffrey Golas <jeffg at junknet.net> wrote:
>>>>>>
>>>>>> 
>>>>>> Dont use sandpaper! The MA is important as it does affect the
>>>>>> waveforms. The machine wants to see 60ma whether it's 120vdc or
>>>>>> 15vdc. Set the scope to be wide enough to get an entire character
>>>>>> if you havent already, it almost looks like the pic may just be
>>>>>> showing the stop bit (33ms?).
>>>>>>
>>>>>> Dial in the loop first, verify its 60ma at idle.
>>>>>>
>>>>>> Jeff
>>>>>>
>>>>>>> On Aug 6, 2023, at 9:05 AM, Eric Moore <mooreericnyc at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> 
>>>>>>> https://deramp.com/downloads/teletype/Model%2015/loop%20interface%20board/Schematic%20Rev%20A.pdf
>>>>>>>
>>>>>>>
>>>>>>> Verified the printer loop at 60ma. The keyboard loop runs at 15V,
>>>>>>> not sure on the ma, but not sure it matters much as it just opens
>>>>>>> and closes without driving any coils or similar.
>>>>>>>
>>>>>>> I am fairly certain my issue is the contacts somehow. I see
>>>>>>> voltage (and continuity) up to those contacts, but despite
>>>>>>> cleaning fairly extensively with contact cleaner, they are still
>>>>>>> too high resistance. I am going to try some sandpaper today and
>>>>>>> see what is what...
>>>>>>>
>>>>>>> -Eric
>>>>>>>
>>>>>>> On Sun, Aug 6, 2023, 12:10 AM Gerry Block <gblock at sbcglobal.net
>>>>>>> <mailto:gblock at sbcglobal.net>> wrote:
>>>>>>>
>>>>>>>     typo:  "60 ma"
>>>>>>>
>>>>>>>     Sent from my iPhone
>>>>>>>
>>>>>>>>     On Aug 5, 2023, at 10:07 PM, Gerry Block
>>>>>>>>     <gblock at sbcglobal.net <mailto:gblock at sbcglobal.net>> wrote:
>>>>>>>>
>>>>>>>>     eric
>>>>>>>>
>>>>>>>>     what does your loop schematic look like?  sketch it out and
>>>>>>>>     enclose photo.
>>>>>>>>     what is the loop power supply voltage.
>>>>>>>>     what is the series resistance to make the 60ms.
>>>>>>>>     are you sure it is running at 60 ms?
>>>>>>>>     where is the scope probe grounded and where is the loop
>>>>>>>>     supply grounded?
>>>>>>>>     i doubt it is the contacts.
>>>>>>>>
>>>>>>>>     gerry
>>>>>>>>
>>>>>>>>     Sent from my iPhone
>>>>>>>>
>>>>>>>>>     On Aug 5, 2023, at 5:49 PM, Eric Moore
>>>>>>>>>     <mooreericnyc at gmail.com <mailto:mooreericnyc at gmail.com>>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>     
>>>>>>>>>     I have cleaned with contact cleaner and paper tape pretty
>>>>>>>>>     extensively, but can always go another round.
>>>>>>>>>
>>>>>>>>>     I do not think that is a good waveform, but similarly, no
>>>>>>>>> idea.
>>>>>>>>>
>>>>>>>>>     -Eric
>>>>>>>>>
>>>>>>>>>     On Sat, Aug 5, 2023, 7:23 PM Jeffrey Golas
>>>>>>>>>     <jeffg at junknet.net <mailto:jeffg at junknet.net>> wrote:
>>>>>>>>>
>>>>>>>>>         Correct me if Im wrong but could just be "dirty"; as
>>>>>>>>>         the cam rubs against the switch youre seeing noise like
>>>>>>>>>         a dirty volume pot.
>>>>>>>>>
>>>>>>>>>         Id use some alcohol and a business card and scrub the
>>>>>>>>>         contacts (plus Im not sure thats even a terrible signal
>>>>>>>>>         for a 1940s device. Going machine to machine I dont
>>>>>>>>>         think that tiny bit of leakage woulda mattered.
>>>>>>>>>
>>>>>>>>>         Again, correct if wrong, Im here learning too.
>>>>>>>>>
>>>>>>>>>         Jeff KC3GJX
>>>>>>>>>
>>>>>>>>>     ______________________________________________________________
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>>>>>>>>>
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>>>>>>>>>
>>>>>>>>>     This list hosted by: http://www.qsl.net
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>>>>>>>
>>>>>> ______________________________________________________________
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>>>>>>
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>>>>>
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>>>>>>>> 1998-to-2001 greenkeys archive:
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>>>>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>>
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>>>>>> 2002-to-present greenkeys archive:
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>>>>>> 1998-to-2001 greenkeys archive:
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>>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>
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>>
>>
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>>>>> 2002-to-present greenkeys
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>
> ______________________________________________________________
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>
>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>> https://teletype.net/gksearch
>>>> 2002-to-present greenkeys archive:
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>>>> 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
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> Message delivered to harold at w6iwi.org


-- 
Not sent from an iPhone.

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