[sdiy] Mystery Vactrols/Photocouplers

[Peter Grenader]

Not seen these b4, but one thing you may wish to try if the knowledge base
here comes up shrugging it's collective shoulders:

Pull them out, slap together a simple :LED driver (like a pot with a current
limiter or something along those lines) and measure the resistance of these
guys. You may be able to find a suitable 21st century replacement.  Of
course decay time will factor into this, but you can also approximate that
measurement with the jig I've suggested.  Don't give up with the idea of
approx. replacements until you give them a listen - you may find that your
sub works just fine within the entire bowl of soup.

If it turns out that these have some odd-ball max resistance, you can
circuit bend vac's of higher values much like you can pots by limiting their
on resistance with a resistor in parallel.  And although he is credited for
many shall we say  'creative' (cough cough) solutions , Buchla did just this
in the AGC of the original 291 input stage.

hope this helps,

- P



BrightBoy wrote:

> All:
> 
> I'm in the process of reverse engineering the tri-stereo chorus
> rack unit and I'm wondering if anyone recognizes the two
> photocouplers that are used in this device:
> 
> http://www.mindspring.com/~jdec/gtr/mystery.jpg
> 
> The device with the "4G" marking has two leads on one end
> and 4 leads (2 pairs) on the other.
> 
> The device with the "4H" marking has two leads on each end.
> 
> Any help would be greatly appreciated!!!!
> 
> Cheers,
> 
> Jeff
> 
> 
> 
> 
>