Bill,
Thanks for taking the time to produce this thread. As a past owner of this camera model it was great to see the pictures and description of the internal parts. As you know, that pan/chop switch had me scratching my head until you explained it to me.
I may not have the P4428 any more but I do have it's descendant, the ARGUS1. I have three that will need my attention so any information pertaining to these Pyroelectric Vidicon cameras is always of interest to me.
These tube based cameras may seem very 'old school' when compared to modern microbolometers but, as you well know, uncooled thermal sensor technology was very much in its infancy when this camera was designed and advances came in small steps. Many clever people understood the principles of the venerable Vidicon monochrome television camera tube, but some clever clogs thought to use a thermally reactive target material to form a thermal scene sensitive television tube. Genius
Building on what you know and understand is often a good start and this technology proved itself in several cameras of the period.
On the Fire TICS forum you kindly documented returning one of these tube based thermal cameras to service through correct setting of the various tube bias voltages etc. Thanks to your efforts, some people who either have a somewhat tired tube based camera, or those who cannot afford the later BST/microbolometer based cameras, have a chance of owning a useful thermal camera based on this technology.
Thanks again
Fraser