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A review of EMI pre-war TVs (by a famous person)

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
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A review of EMI pre-war TVs (by a famous person)

Post by Brianc » Sat Aug 06, 2016 6:46 pm

How about this for a letter? From the chief instigator of the 405line TV system to his very forward looking boss. It is also interesting that it ties up a bit with the removal of the gamma correctors at AP after the war when the CRTs were more likely to be triodes than pentodes or hexodes - or does it?
Blumlien-Shoenburg Letter_Page_1.jpg
Blumlien-Shoenburg Letter_Page_2.jpg

Jon - you may want to put this on your website!

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by CTV » Sat Aug 06, 2016 7:06 pm

Hi Brian,

What a gem and fascinating to read too. To think written just one week before the start of WW2 and the infant TV service being put into hibernation for the duration.

How did you come by the letter?

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Brianc » Sat Aug 06, 2016 8:18 pm

A very good friend of mine, Norman Green, has been researching the history of EMI television for many years now and he discovered this letter last week in an archive he was examining - I'm not sure which but I'll find out.

I've just found out that Norman found it in the Walter Leonard Watton papers in the IEE archives. Watton joined EMI in 1933 to work on TV IF amplifiers.

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Kalee20 » Mon Aug 08, 2016 12:50 pm

Wow. ADB himself. Pity it's only a copy, not signed.

What's all that about the 'weak hold' control? Sounds interesting!

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Jac Janssen » Mon Aug 08, 2016 3:18 pm

Hello Brian,

That's very interesting.
What puzzles me is the named bandwidth of 1.2 Mc/s, "which is basically similar to the type 901".
The 901/702 though appears to have no problem with 2.5 MHz, and shows (although weakly) the 3 MHz bars.

Are there any 1801 or 1802 receivers still in existance?

Jac

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Brianc » Mon Aug 08, 2016 7:41 pm

Jac Janssen wrote:Are there any 1801 or 1802 receivers still in existence?Jac
Hi Jac
According to the ETF, there are no known survivors - did they go into production? - I doubt it if their performance was being reviewed a week before the TV service closed down.

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by peter scott » Tue Aug 09, 2016 7:32 pm

Thanks very much for posting Brian. It is fascinating. It would be wonderful if Norman Green wrote a book on that period of EMI. I've just been reading Robert Alexander's book on Blumlein but find it rather disappointing.

Jac Janssen wrote:Hello Brian,

That's very interesting.
What puzzles me is the named bandwidth of 1.2 Mc/s, "which is basically similar to the type 901".
The 901/702 though appears to have no problem with 2.5 MHz, and shows (although weakly) the 3 MHz bars.

Are there any 1801 or 1802 receivers still in existance?

Jac


They are quoting the bandwidth at 150uV. I've not tried aligning my 901 for "NORMAL" sensitivity which is quoted as 50 to 60uV but I find it very easy to lose bandwidth with minor adjustment changes. The "WIDE" alignment that I have used (and I think you too Jac) is quoted with a rather less impressive 200 to 300uV sensitivity.

Peter
Image

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Jac Janssen » Tue Aug 09, 2016 7:58 pm

Hello Peter,

I tried to align according to the "normal" instructions, but that didn't go too well.
So I aligned for a reasonable bandpass curve as best as I could.
I thought I made a note about the sensitivity, but I can't find it now. The sensitivity certainly is good.
2015-10-26 702 650 TCC a.jpg

2015-10-26 702 651 TCC.jpg

Sorry for the bad photos. (note also some bad spots on the mirror.)
The overal vision bandwidth touches 3 MHz, but unfortunately the CRT is so weak that it is very difficult to get an acceptable focus.
Otherwise the 702 functions quite well. It has the push-about coil, and indeed needs it to get the picture centered.

Jac

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Brianc » Wed Aug 10, 2016 8:02 am

That's a super testcard, Peter. You certainly have a good CRT there. The vendor of my 702 said that he had tried my CRT in his other 702 and that it is very good so here's hoping!
Jac, Norman has given quite a few lectures on the history of EMI TV and if you search for Norman Green, you will find a recording (Royal Television Society, I think. There is also a presentation I gave called "An Evening with Brian Cuff" which might amuse you!!

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Till Eulenspiegel » Wed Aug 10, 2016 11:01 am

Hi Brian,
just like the problems being experienced in the GEC BT8161 it is certain because of the low IFs in the 1801 and 1803 receivers that vision bandwidth problem manifested itself again.
The 901 is a different matter, being a TRF receiver operating at 45mcs it is much easier to achieve a wide bandwidth and in fact this receiver operates with a near symmetrical vision passband characteristic.
Interesting to learn that A. D. Blumlein was critical of one of his companies' products, the HMV 1801.

Till Eulenspiegel.

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by peter scott » Wed Aug 10, 2016 11:09 am

Thanks Brian. I had enjoyed watching your video some time ago but I hadn't seen Norman's IEE presentation before and did find it very interesting. Jac is being very modest with his screen photos. I've never been able to tune my vision RF strip to get more than a suggestion of the 3MHz bars. You can see them on Jac's first picture if rather softened by his old CRT but displayed on a modern tube his RF strip shows a really crisp set.

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Jac Janssen » Wed Aug 10, 2016 11:51 am

Thanks Brian for the pointer to your video! I'm certain going to look at it with pleasure.
Couldn't locate the Norman Green video('s) though.
Perhaps it is permitted here to place a direct URL?

The testcard of Peter is very impressive. I'm especially envious of his good focus all over the picture area.

The TRF-section in my 702 indeed is capable of 3 MHz.
Here it is connected to an adapted (very old computer-)monitor:
2015-09-25  TRF TCC Aurora op Taxan na tweaken.jpg

Due to the very sturdy mask, I had to employ the push-about coil to center the picture. All in all it does not degrade the focus much. Well... it was already bad enough as it is...

Jac

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by CTV » Wed Aug 10, 2016 12:00 pm

Just watched Brian's excellent video, to save you all searching here it is


 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by peter scott » Wed Aug 10, 2016 1:21 pm

Jac Janssen wrote:Thanks Brian for the pointer to your video! I'm certain going to look at it with pleasure.
Couldn't locate the Norman Green video('s) though.
Perhaps it is permitted here to place a direct URL?
Jac


Jac, Unfortunately the lecture I watched requires IET membership or payment to view: https://tv.theiet.org/?landscapesearchresult
I entered "Norman Green EMI" into the search box.

Peter

 
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Re: A review of EMI pre-war TVs (by a famous person)

Post by Jac Janssen » Wed Aug 10, 2016 3:43 pm

Peter,

I'm not an IET member, but thanks anyway.

Jac


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