Pro Audio Design Forum

Audio Scape has UREI T4B modules and replacement EL panels.

An accurate clone of the vintage T4A and T4B optical cells used in the original LA2A and later LA3A's. Each unit is painstakingly handcrafted using the finest components and years of research and design to create an accurate and affordable clone of the original T4's. The goal of these is to model the original T4's that are found in the vintage units from the 60's, not the newer reissue units which are slightly different in approach.

http://www.audio-scape.com/category-s/103.htm

Kenetek seem to be the resident experts in this. I'm sure Bill could give us a blow by blow.

Thanks Doug. I read Bill's articles. http://www.kenetek.com/OtherStuff/About ... fault.aspx

The one thing I've never seen discussed is the change in chromaticity of the EL panel versus applied frequency.
The EL panels shift from yellowish green to blue versus frequency due to the change in current with constant-voltage drive.
With the CL-505 photocells having a peak at daylight yellow and the spectrum of the source being offset from that (and shifting with frequency) it's got to be a very complex thing to get right.

With regard to one of Bill's comments.
My bet is that the mesh in the T4B is an electrostatic shield.
There's too much drive voltage on the EL side and a high enough impedance on the photocell side that the capacitive coupling would be very large without it.