PWM style compressor

[Eric]

>This would probably be a Cat-eye tube and not a e.l. pannel

No. The Teletronix LA-2A used a small electroluminescent panel
shining onto an LDR.
(The EL effect was discovered a LONG time ago.)
Such panels have been marketed since the early 1950s as nightlights.
They are made to plug right into the AC mains socket. Sylvania was
the first to make them, today there are several companies making
EL nightlights. Modern panels are not much different from the
old ones, except possibly better/purer materials for longer life.

Eric Barbour
METASONIX