Vactrols

[para]

this is an attempt to gather all of the available info about Optocouplers / vactrols in one place. if you come across anything at all worth adding please do.



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here is a fantastic vactrol write-up by Scott Stites taken from his WSG mod page found here  -  http://mypeoplepc.com/members/scottnoan ... /id16.html



'"Vactrol' is the trademarked name of an optoisolator, also referred to as optocouplers, formerly manufactured by Vactec, now manufactured by Perkin-Elmer. An optoisolator is a single, light-proof package containing an LED and one or more Light Dependent Resistors (LDR). An LDR, or photocell, has a resistance that varies with the amount of light striking its surface. In the case of the optoisolator the amount of current passing through an LED determines how brightly the internal LED shines, which affects the resistance of the LDR built into the same case. Note that these devices are not the same type of device that contains an LED and a light sensitive transistor or diode, it must be an LDR. Different optoisolators have different characteristics - the value of 'on' resistance, the value of 'off resistance', and, just as important, the amount of time it takes for the LDR to reach its 'on resistance' from a state of 'off resistance', and the amount of time it takes the LDR to reach its 'off resistance' from its 'on resistance'. Some LDR's take longer to reach these two states than others. Some manufacturers make LDR's that are very, very fast. Others are very, very slow. All LDR's will normally take less time to go from light (on) resistance than time it takes to go to dark (off) resistance. These time factors can be thought of as the 'attack' and 'decay' of the optoisolator.  by Scott Stites"

scott also wrote an impressive article describing how to "roll your own" vactrol found here - http://experimentalistsanonymous.com/bo ... .php?p=874


i also wanted to note that an Optocoupler is a form of Optoisolator - but generally "isolators" are used as switches so if you're searching around use Optocoupler or you may no find what you are looking for



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allied electronics and small bear are two of the only places that still carries new vactrols in varius flavors –

http://www.alliedelec.com/  

http://www.smallbearelec.com/Categories ... tocouplers



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silonex vactrols are the cheapest and they come in many different resistance ratings. check each datasheet for the max "off resistance"

http://www.alliedelec.com/Search/Search ... tk=Primary



PerkinElmer Optoelectronics make the nicer vactrols but they are also more expensive. they also make a dual vactrol. these are some of the most commonly used models

VTL5C3  - 10M
http://www.alliedelec.com/Search/Produc ... 80537EE17F

VTL5C3/2 - 10M dual
http://www.alliedelec.com/Search/Produc ... 980%2D0730

and many more
http://www.alliedelec.com/Search/Search ... 802574E17F



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general vactrol link -


Cynthia Breaksdown Vactrols
http://www.youtube.com/watch?v=xoTcHI2O ... ben%2Ehtml

opto-phaser
http://www.aleph.co.jp/~takeda/radio/phaser/indexE.html

vac-talk
http://www.midibox.org/dokuwiki/doku.ph ... nalog_gear

diy vactrol
http://www.notbreathing.com/img/homevactro.jpg

diy vactrol synth
http://web.mac.com/ainglizian/iWeb/a%20 ... 0004-4.JPG

diy vactrol distortion
http://www.getlofi.com/uploaded_images/ ... 753400.JPG




local vactrol threads -

http://experimentalistsanonymous.com/bo ... .php?t=139

http://experimentalistsanonymous.com/bo ... php?p=2273




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[Roycie]

Here's a pretty cool article on how to build your own, by Grant Richter of the Wiard Synthesizer Company.
http://www.musicsynthesizer.com/Hairball/hairball.html

[Haman03]

Vactrols have been used as remote-controlled resistors for precise ground termination of Beverage and Ewe type antennae. In a typical ham radio setup, the vactrol is placed in the termination box at the farthest point of the antenna. The LDR modifies total resistance between antenna and ground (termination resistance); the operator fine-tunes this resistor from his radio shack by varying the vactrol's LED or bulb current with a potentiometer. Tuning with vactrols improves directional cardioid pattern of the antenna. According to Connelly, vactrols are superior to traditional resistors in this function. In this simple layout, the LED or bulb of the vactrol is prone to damage by voltage surges induced by lightning, and must be protected by a pair of neon lamps acting as gas dischargers.