Golborne Vintage Radio

I have been sorting and testing my way through a ton of vintage valves this week, sad really but whatever turns you on.
Found some lovely bottles, MU14, HR210, ARDD5, VT127, VT50A, CV1722, CV1120 etc. and then I found a very odd looking GT sized Int Octal glass bottle, a 923.
Numbered very clearly but cannot find any reference. Closest is 922 which is a photocell so I am assuming that this 923 is as well. Looks like a curved reflector with an electrode at the focus.
Can anyone elaborate on this?

is this the one?
http://www.tubecollector.org/923.htm
Rob T

More
http://www.mif.pg.gda.pl/homepages/frank.../9/923.pdf
Rob T

Yes, so fast too.
This is not a site that I have seen before, nice one.
Funny it never turned up on a Google search.
Is this any use to anyone? Or can I test it?

Here's some guff on RCA photo tubes including the 923, typical applications etc from the RCA 1941 photo tube book of words:

https://ia601902.us.archive.org/13/items...1_text.pdf

Lawrence.

I have got a couple of them too. They would have been used is sensors for the optical sound track on cinema projectors.