Vintage rear projection sets

[DODGERN]

Can anybody remember the post war rear projection sets. These sets were the forerunner of the larger screen sets that were to follow.
They used a small CRT of the size used in wartime radar. The image was projected via a series of mirrors onto a screen. I seem to think that they had mains generated EHT.
The works of one of these sets was displayed, the CRT anyway, in a model village on Yarmouth seafront. Looking into the model house all you could see was a small television picture. Holidaymakers would marvel at the tiny set. The rest of the set was hidden behind and underneath the house out of sight!
The attachment is an early RCA American model. Sorry about the picture quality, blame Mr. Google.

Roger.

[Mark R]

There is this one

http://www.thevalvepage.com/tv/feranti/20t6/20t6.htm

which I now have for doing.

cheers Mark

[DODGERN]

Will be great to see it when you get it going Mark.

Roger.

[Mark R]

Roger
That will be a big dollop of courage for that one. I have no doubt Steve P and Dave Williams will give a prod though!

cheers Mark

[Steve_P]

It depends what the EHT is. If it's mains derived, it will kill. If not, be very careful anyway as the EHT is 25kV. If the tube is ran without the field or line stages working, it will be ruined instantly. They burn a line across the tube in seconds.

There aren't many times when I say 'be careful' but these projection sets are a different matter. Be Careful. No drawing sparks with screwdrivers for fun - tell Dave that from me, Mark.

Apart from that, it's simple enough.

Cheers,

Steve P.

[AlanBeckett]

I don't understand the Notes on Jon's website. If Va screen voltage is the inverse of Va Anode voltage, and Vb inverts it - it's a Common Cathode stage - how does that make the Anodes of Va and Vb opposite?
Alan

[Duke Nukem]

I agree Alan - 7 years later it doesn't make sense the way its written to me either. It only works if the screen current increases with increasing anode current. If the anode volts much greater than screen (low anode current), then the electrons would favour the anode. If the anode volts much lower than screen (high anode current) then the electrons would begin to see the screen as a more favourable target, so more screen current. So I can argue the currents being in phase, so where did I get it in my head they were anti-phase ? [Answers on the back of a crisp ten pound note please].

TTFN,
Jon

[Mark R]

Saved by Jon...............kind of!

no tenners here!

cheers Mark

ps still have to fix the thing, currently looking for a lead vest!

[AlanBeckett]

Jon,
Normally the Screen is decoupled and hence stays at substantially the same voltage, or at least I always assumed so. What happens with an undecoupled Screen, particularly if it's fed from a relatively high restance, I haven't a clue.
Some research is called for.
Alan

[Brianc]

I would say the projection sets are as safe as any other non-mains derived TV. Just don't run the EHT generator without the tube EHT lead being plugged into the CRT. Even then, the impedance of the source is higher than the old over-wind/EY51 supplies as it uses a tripler. No-one takes any notice of the EHT in a colour set - that's normally 25kV as well, also from a tripler so really, just be careful!
Nice looking set, by the way. I have some spares for projection sets (optics) if you need any but be warned, the Schmidt corrector lens is normally ground for specific optical paths so they're not always compatible.