A Good Projection System?

[peter scott]

I was picking through the list of BBC Engineering Reports looking for something else and came across a test of a Philco Projection set that received a very favourable report. Instead of the usual Philips MW6-2 etc the Philco used a 4" tube and projected it onto the front of a slightly concave screen.



I suspect that if you lived in anything by way of a dusty environment then it would be a right pain for the cleaning but I would certainly be interested to see one in operation.

Peter

[Jac Janssen]

Hi Peter,

Interesting set.
I can imagine that the brightness is better with the larger tube. But the light losses might be a bit higher than with the Schmidt optics for the MW6-2 that Philips used in the experimental set and in the later projection sets.
The experimental set uses a special ground viewing screen ( a bit like finely sandblasted glass), but the later sets use a pressed plastic one with  pressed-in Fresnel-like lenses.
None of these Philips sets required welding goggles or sun glasses

   

Jac

[peter scott]

Hello Jac,

I thought you might be interested. I'm not sure to what extent the image on the CRT is keystoned. I did wonder if it wasn't a very efficient use of the 4" screen. The angle of the optics to the flat mirror would suggest quite extreme keystoning. It was the BBC reaction to its performance that I thought was really interesting. The 60 degree horizontal viewing angle sounds a bit restrictive but they don't raise a major objection to that.

I have no doubt that you are aware of the BBC report on their visit to Philips in 1946 with very interesting comparisons of the Philips (RCA) Iconoscope to the Emitron and thoughts of replacing Emitrons in BBC cameras.

Peter

p.s. That's a super picture of your 567 line test card image.

[Murphyv310]

Hi Peter,

Interesting set.
I can imagine that the brightness is better with the larger tube. But the light losses might be a bit higher than with the Schmidt optics for the MW6-2 that Philips used in the experimental set and in the later projection sets.
The experimental set uses a special ground viewing screen ( a bit like finely sandblasted glass), but the later sets use a pressed plastic one with  pressed-in Fresnel-like lenses.
None of these Philips sets required welding goggles or sun glasses



Jac

What a cracking picture. Perfect linearity and geometry, Looks like a stuck on photo

[Kalee20]

Interesting that the line output stage had enough design margin to enable operation at 10.125kHz, that's down by 35% from American!

[Jac Janssen]

Thank you Peter and Trevor,

The restoration of this set took a lot of work over a long time span.
I had very little, if any, documentation of it and not much was known of it.

It is for the experimental 567 line transmissions of Philips, who tried to push the 567 line standard in Europe, but did not succeed in that.
A 405 line version of this set was also made (1 year before my 567 set), but I have never seen or heard of one still in existence.
As far as I know, my 567 line projection set is the only working one that exists.

Th 567 line standard is close to the 625 line standard, but with a reduced number of lines and a reduced video bandwidth. The picture and sound carriers are only 4.5 MHz apart, as opposed to the continental standard of 5.5 MHz for 625. Vestigal sideband, neg video-modulation and FM sound.

Originally I had restored the to 625 lines, but when it was possible to generate 567, I aligned it to 567.
For this I changed a Hedghog standards converter to converter to 567 i.s.o. 405. With lots of help from Frank and Jeffrey!

Jac

[ppppenguin]

Interesting that the line output stage had enough design margin to enable operation at 10.125kHz, that's down by 35% from American!

It's only scanning a tiny, narrow angle, CRT. Albeit with a high EHT. I would expect such a LOP to be easily operable over a wide range of frequencies.

I assume EHT is separately made, as with sets using the MW6/2.

[Jac Janssen]

Hi Jeffrey,

Yes, the EHT is made with a separate generator, like in later projection sets.

Jac

[Murphyv310]

Hi.
The Decca 1000 will run 5Khz to 16Khz so covers 240 and 625 lines with only slight cramping on the left hand side.

[Jac Janssen]

Hi Trevor,

I saw a picture once of your Decca 1000: excellent picture!

Jac