[GreenKeys] [External] Tip on loops

[Frank Carraro]

 Well I guess those days are gone forever.  Where can anyone buy incandescent lamps anymore?   Hey, I used them in animalcages to keep newborns warm.   Yeah, I know they can be found in some stores and especially certain special applications, but...
    On Friday, October 4, 2019, 4:35:51 PM EDT, Bruce Gentry via GreenKeys <greenkeys at mailman.qth.net> wrote:  
 
  
The varying resistance of incandescent bulbs has beeen used in many? ways over the years. One of the more interesting was a volume expander for console radios using a bridge of fixed resistors and low voltage bulbs between the audio amplifier and loudspeaker. For many years I used large light bulbs for troubleshooting relay logic elevator controllers. If a 1 or 2 amp fuse kept blowing, I would put a 200 watt light bulb in place of the fuse and begin checking things out. It would usually just barely glow until an operating sequence powered up a circuit with a short. It was far better than blowing a dozen fuses and welding relay contacts.? The inrush current of bulbs can be useful as well.? On one moderization job, there were several service calls a day, all related to bad door interlock contacts. The original interlocks were re-used, but they were now carrying 120 volts AC at about 10 MA., instead of? 240 Volts DC at about 2 amps. I added a 100  watt light bulb to load the contacts and burn them clean, the service calls dropped to one a month. Some sniveling 23 year old in mangement discovered what I had done, and ordered the bulb removed. Within a few days, there were several service calls a day. I refused to answer them, causing serious conflict. The calls suddenly went away. Later, I did go on a call there, and the bulb was back in the circuit.? Electromechanical stuff and relay logic control circuitry are very interesting, and are becoming a lost (supressed) art.? 
 
 

 
 
????? Bruce Gentry, KA2IVY
 
 
?????? 
 
 On 10/4/19 4:06 PM, Jones, Douglas W wrote:
  
 On Oct 4, 2019, at 2:28 PM, Jim Haynes wrote:

 
 ... The reason for this is the temperature
coefficient of resistance in the metal filament.  As current increases
the filament gets hotter, increasing its resistance and tending to
reduce the current.
 
 I vaguely recall some interesting circuits that I recall seeing in the 1960s that used incandescent bulbs as active elements, exploiting both the non-constant resistance of the bulb and the thermal time-constant of the filament. Doug Jones jones at cs.uiowa.edu______________________________________________________________GreenKeys mailing listHome: http://mailman.qth.net/mailman/listinfo/greenkeysHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:GreenKeys at mailman.qth.net2002-to-present greenkeys archive: http://mailman.qth.net/pipermail/greenkeys/1998-to-2001 greenkeys archive: http://mailman.qth.net/archive/greenkeys/greenkeys.htmlRandy Guttery's 2001-to-2009 GreenKeys Search Tool: http://comcents.com/tty/greenkeyssearch.htmlThis list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.htmlMessage delivered to ka2ivy at verizon.net 
 
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