I've been trying to get my hands on some Vactrols (opto-variable resistor) for a long time, unsuccessful. Not even digikey has them.
some examples: VTL5C2, VTL5C3, NSL32
Can't see them as "too expensive to manufacture" considering you can improvise one using an LED+LDR+Tape, but it's in no way as "linear" or robust as the actual components.
Anyone knows the story behind it?
Edit: So there are places where you can get them, but at least where I live it's something almost unheard of.. They look usefull in many ways (at least to me), yet I've seen them nowhere except some old audio equipment..
Edit2: Ok, so what could be the alternative to a vactrol if I require exactly that, a significant resistance change controled by voltage, (MOSFET as resistor is not an option for me because of the very low resistance range). Is there such a device/equivalent circuit that allows all this with the simplicity of the vactrol? This is a hypothetical question, based on many compressor units I have seen and seems Hard to achieve such functionality in such a simple way, the closest I've seen are OTA based for closed loop circuit, but they arent nearly as simple as vactrols.