
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.
VTL5C3/2
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.
VTL5C3/2 

Brand 
Current 
#1 
#2  #3  #4  
Left  Right  Left  Right  Left  Right  Left  Right  
Xvive  1 mA  59K  52K  39K  38K  60K  54K  123K  90K 
Excelitas  22K  21K  86K  78K  68K  63K  52K  48K  
Vactec  16K  16K  26K  27K  
PE Spec  55K  55K  55K  55K  55K  55K  55K  55K  
Xvive  2 mA  23K  21K  14K  14K  21K  19K  29K  24K 
Excelitas  9.3K  8.7K  31K  29K  25K  23K  19K  17K  
Vactec  8.4K  8.3K  11.8K  12.5K  
Xvive  5 mA  9.0K  8.5K  5.6K  5.3K  8.4K  7.7K  8.9K  7.6K 
Excelitas  3.3K  3.0K  10.6K  9.7K  9.0K  7.5K  6.3K  5.8K  
Vactec  3.7K  3.7K  4.7K  5.0K  
Xvive  10 mA  5.2K  5.0K  3.3K  3.1K  5.0K  4.6K  4.5K  4.0K 
Excelitas  1.5K  1.5K  4.8K  4.5K  3.7K  3.5K  2.9K  2.7K  
Vactec  2.2K  2.2K  2.5K  2.7K  
Xvive  20 mA  3.3K  3.2K  2.1K  2.0K  3.3K  3.0K  2.6K  2.4K 
Excelitas  880R  830R  2.6K  2.5K  2.0K  1.9K  1.6K  1.5K  
Vactec  1.3K  1.3K  1.4K  1.5K  
Xvive  40 mA  2.2K  2.2K  1.6K  1.6K  2.2K  2.3K  1.5K  1.6K 
Excelitas  600R  560R  1.8K  1.6K  1.3K  1.2K  1.1K  1.0K  
Vactec  910R  890R  920R  950R  
PE Graph  1.5K  1.5K  1.5K  1.5K  1.5K  1.5K  1.5K  1.5K 
The PerkinElmer 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".
VTL5C3
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.
VTL5C3 

Brand 
Current 
#1 
#2  #3  #4 
Xvive  1 mA  32K  26K  21K  29K 
Excelitas  35K  24K  14K  18K  
PE Spec  30K  30K  30K  30K  
CA Spec  10K  10K  10K  10K  
Xvive  2 mA  14K  13K  8.8K  12K 
Excelitas  14K  9.5K  6.3K  7.5K  
Xvive  5 mA  6.1K  5.5K  3.5K  5.2K 
Excelitas  4.5K  3.0K  2.3K  2.5K  
Xvive  10 mA  3.5K  3.3K  2.0K  3.0K 
Excelitas  2.0K  1.3K  1.1K  1.3K  
PE Graph  4K  4K  4K  4K  
CA Spec  1K  1K  1K  1K  
Xvive  20 mA  2.2K  2.0K  1.2K  2.0K 
Excelitas  1.1K  730R  647R  730R  
Xvive  40 mA  1.5K  1.4K  800R  1.3K 
Excelitas  700R  467R  647R  730R  
PE Graph  1K  1K  1K  1K  
CA Spec  500R  500R  500R  500R 
The PerkinElmer 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.