<html><head><meta http-equiv="content-type" content="text/html; charset=us-ascii"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Also cover them / shine a light on them. I once had a vactrol (NVOS) that behaved funny sometimes, so I replaced it with another one. Afterwards I found something that looked like a small crack near one of the leads, so I assume that some light leakage came in. (Or perhaps it was just moisture.)<div><br></div><div>Ben<br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On 20 Oct 2025, at 01:07, crystal via Synth-diy <synth-diy@synth-diy.org> wrote:</div><br class="Apple-interchange-newline"><div>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<div text="#000000" bgcolor="#FFFFFF"><p><font size="4">Yes, that circuit sounds good. I think i can just
go the breadboard, scope, meter route again. </font></p><p><font size="4">Indeed, some of the optos took forever to get
back to off voltage and the on and off timings were very
inconsistent. It's not mission critical and i still have some
separated (somewhere). </font><font size="4">I use them to
modifry synth pcbs to add CV to circuits that didn't have those
functions (i use OTAs also but optos are easy). </font><font size="4">I'm just digging my workshop out of a storage unit
after a 9 year hibernation, planning to get back to synth
building with state of the art, cutting edge (1987) tech.</font></p><p><font size="4">thanks</font></p>
<div class="moz-cite-prefix">On 10/19/2025 11:43 AM, Oren Leavitt
via Synth-diy wrote:<br>
</div>
<blockquote type="cite" cite="mid:79abd6f7-d79a-42f5-9541-27b217920c20@proton.me">
<pre wrap="" class="moz-quote-pre">Some years back, I made a Vactrol test circuit for quickly analyzing and
matching Vactrols.
Basically a standard "cheap LFO" integrator/comparator w hysteresis
oscillator, but using the Vactrol under test in place of the integrator.
The photocell side would go to the comparator input and the comparator
output would drive the LED thru a current limit resistor. A series
resistor from V+ with a pot is used to set a nominal current thru the
photocell.
I can look at the frequency, shape and amplitude of the repeating
"attack/decay" waveform on an oscilloscope as a quick analysis of the
Vactrol.
-Oren
If I find or recreate the circuit, I'll post it here.
On 10/19/25 3:58 AM, crystal via Synth-diy wrote:
</pre>
<blockquote type="cite">
<pre wrap="" class="moz-quote-pre">Can someone point to a testing circuit for "Vactrols?"
I bought a bag full of Siliconex optos years ago, they are all over the
map in response time.
I had tested quite a few in a very crude breadboard setup, mostly just
looking at on/off resistance timing and off resistance and then putting
them in envelopes with details written on them. I'm sure i could do that
again, i'm just wondering if it's been done better.
thanks,
Crystal
</pre>
</blockquote>
<pre wrap="" class="moz-quote-pre">
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