Vactrols have gone through a number of manufacturer changes. Vactec is the first manufacturer of vactrols and who originated the name. In 1983 they were acquired by Perkin Elmer. In 2010 this group in Perkin Elmer was spun out and became Excelitas Technologies who manufactured them until 2010. CoolAudio is manufacturing the VTL5C3 and Xvive is manufacturing a complete line. I find a number of vactrols in my repair work where the range is just too high for the circuit to operate properly. In some of my builds I match vactrols and notice that they vary wildly. I decided to document random samples of different brands I have available.
I only had two samples of the original Vactec and they differed at low currents but matched up nicely at higher currents and the resistance side to side was also well matched. Both the Excelitas and Xvive varied widely in performance.
For the Xvive, #1 and #3 are the closest matched. For the Excilitas, #2 and #3 are closest matched.
The Perkin-Elmer specification for the VTL5C3/2 is a bit confusing. The characteristics table shows a 2R on resistance at 40 mA which is extremely low for a CdS photocell. However, the graph shows a more reasonable ~1.5K. I don't understand why such a large difference unless they dropped a "K".
Both the Excilitas and Xvive varied widely in performance. For the Xvive, #2 and #4 are the closest matched although they all tended to converge at the higher currents. For the Excilitas, #3 and #4 are closest matched and likewise they tended to converge at at the higher currents. In general the Excelitas were lower resistance than the Xvive at currents above 5 mA.
The Perkin-Elmer specification for the VTL5C3 is likewise confusing. The characteristics table shows a 1.5R on resistance at 40 mA which is extremely low for a CdS photocell. However, the graph shows a more reasonable ~1K. Again, I don't understand why such a large difference unless they dropped a "K".
I didn't have a CoolAudio part to test. The characteristics table shows a 500R on resistance at 40 mA and the graph shows a more reasonable ~1K. At 1 mA the characteristics table shows a 10K on resistance and the graph shows ~50K. They still don't match but are more similar.