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Old 24th Jul 2020, 9:27 pm   #21
Duke_Nukem
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Default Re: A TV set with mains EHT - in 1953!

I guess big 15" screens sold in very low volumes, making a redesign expensive if you think in terms of redesign cost per unit. Or maybe they just had a few left over chasiis of the old design, enough to cover low runs of expensive models ?

Mind you if the 2805 is anything to go by, its very good anyway so would be fine for the most up market of models.

TTFN,
jon
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Old 24th Jul 2020, 11:04 pm   #22
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Default Re: A TV set with mains EHT - in 1953!

maybe their in-house winding section could make a mains tx cheaper than developing flyback
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Old 25th Jul 2020, 12:15 am   #23
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Default Re: A TV set with mains EHT - in 1953!

I don't know what the EHT arrangements were, but the Decca large screen projection TVs of the early 1950's (4' x 3' picture) were AC mains only. As well as individual models for all 5 BBC regions, a high fidelity double-sideband model was available to special order, for the London area only.
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Old 25th Jul 2020, 9:03 am   #24
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Default Re: A TV set with mains EHT - in 1953!

I think the Decca projection receivers used the Philips EHT generation with the biscuit tin containing flyback transformer and EY51 triplers.

Peter
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Old 25th Jul 2020, 9:58 am   #25
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Default Re: A TV set with mains EHT - in 1953!

The only Decca TV to employ mains EHT was the original mirror lid 12" BowDecca of 1948 vintage using the first post war Plessey chassis. All British projection receivers used the Mullard system with sealed EHT tripler mentioned by Peter.

English Electric as far as I can remember just dipped their toes into TV manufacturing from around 1951-55. They used an odd arrangement in the 1550 series driving a second power tetrode [185BTA] from the secondary of the line output transformer and A SU25 EHT rect.
The 1650 series used a separate RF EHT unit again with 185BT and SU25. Subsequent models were standard flyback. Their last model was the T40 series. They certainly produced some unconventional models in their short television history. [I believe they were designed by the Marconi company.]
Regards, John.
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Old 25th Jul 2020, 3:00 pm   #26
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Default Re: A TV set with mains EHT - in 1953!

I did wonder why English Electric only made TV sets for a few years, I presume it looked like a good market to enter, but found it less profitable and / or too competitive than they expected.
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Old 25th Jul 2020, 3:24 pm   #27
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Default Re: A TV set with mains EHT - in 1953!

My Father worked for English Electric, at their foundry and plastic moulding works. I once asked him why we had an Ekco rather than an EE. They were too expensive!
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Old 25th Jul 2020, 6:27 pm   #28
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Default Re: A TV set with mains EHT - in 1953!

What was the biggest TV screen in England pre say 1950? I know that you
folks had 15 inchers well before we did, but we pre-1950 had the DuMont 30 inch monster, never equalled in B&W.
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Old 25th Jul 2020, 7:36 pm   #29
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Default Re: A TV set with mains EHT - in 1953!

Yes the Dumont beast with a 30BP4 CRT. Other than specialised non domestic models, 15" was about as large as it got and they were few and far between. The Ekco TC113, Ultra YE72 and the HMV 1803, an early post war 15"example and the slightly later 1806 come to mind. I have no doubt there were a lot more. Regards, John.
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Old 25th Jul 2020, 7:45 pm   #30
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Default Re: A TV set with mains EHT - in 1953!

Quote:
Originally Posted by FERNSEH View Post
Quote:
Originally Posted by barrymagrec View Post

My Dad may still have the mains transformer in his garage if you need one - I think I have the KT44 in my loft....
Rest of it went donkeys years ago.
Actually, I believe the mains transformer is missing in the Marconi VRC52.
Alternatively, if you fancy coming up to Geordieland you can have the set.

DFWB.
Thanks, I need more stuff like I need a hole in the head. I will keep an eye out for the transformer when the inevitable clearout occurs.....
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Old 26th Jul 2020, 5:44 pm   #31
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Default Re: A TV set with mains EHT - in 1953!

I have checked the Ultra data that Hamish mentioned in the Ediswan valve book for 1953 and can confirm the W7106 is not mains derived. A bonus for you! It has two R.F. amplifiers 6F1s, mixer 6F1, Osc vision I.F. 6F1,vision det. half a 6D2, video amp 6F14, sync sep 6L19, frame generator 6K25 [thyratron] line osc. 6F14, line output 6P28, sound I.F. 6F15, sound det/lf amp 6LD20, noise limiter D1, EHT rec. U25. No mention is made as to the type of H.T. rectifier or sound output valve so I presume they are Mullard or metal.
It is a 12" model with a Mazda CRM121A tube. It looks an interesting receiver.

The last mains derived was the 570 [1948/9 series followed by the V600 series that derived it's EHT from an RF oscillator. [P61]

The manufacturers wanted rid of all receivers that employed mains EHT. They were worried about the safety aspects particularly the service engineer. There were a number of fatal accidents.

It was a similar state of affairs with pre war electrostatic tubes. These chassis had mains EHT distributed all over the chassis! From what I have read, when the Television Service restarted after the war, most set makers recalled their receivers and were fitted with the then current magnetic chassis. Murphy and RGD come to mind. I don't think Mazda produced an electrostatic tube as a replacement after the war and Ultra got out of it by declaring that NO spares were available for the pre war models.

I wonder what they would have said if they were told that 70+ years on we would be reviving some of these 'dangerous' chassis. Regards, John.
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Old 26th Jul 2020, 6:00 pm   #32
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Default Re: A TV set with mains EHT - in 1953!

Looking at the HMV 1820 & 1902 sales flyer in post #1, you have to wonder what the prospective buyer would make of RF vs mains EHT.
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Old 27th Jul 2020, 10:54 am   #33
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Default Re: A TV set with mains EHT - in 1953!

Hi Graham,
the details of the EHT supplies were added to the sales leaflet by me.
By 1952 the year the HMV 1820 was introduced the method of generating the the EHT supply by means of an RF oscillator was considered no longer the best method of supplying the CRT final anode. Apart from those 15" models with mains EHT almost every other manufacturer chose to use line flyback EHT.
The 1820 is worthy of separate comment. The 21" Emiscope CRT was a round metal cone type which soon became obsolete and the approved replacement was the Mullard MW53-20. The receiver employed a turret tuner which was loaded with all five BBC channels. Although the tuner resembled the Cyldon type C it's likely it was a Standard Coil Corp. unit. The two valves in the tuner unit was a Z77 for the RF amplifier and a B309/12AT7 mixer-oscillator.
A secondary emission valve was employed in the vision IF amplifier.

DFWB.
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Old 27th Jul 2020, 11:14 am   #34
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Default Re: A TV set with mains EHT - in 1953!

Thank you again John,I must look again and if needed get a photo.CRM121,so it will be flat?
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Old 27th Jul 2020, 6:45 pm   #35
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Default Re: A TV set with mains EHT - in 1953!

No, it should be sort of a round shape..

You never know. There are good ones but it may have an isolation transformer fitted to deal with a heater/cathode short but that does not automatically mean that it is also low emission. They all ended up with a transformer!

At least you don't have the mains EHT hazard to deal with. The valve line up is reliable. John.
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Old 27th Jul 2020, 6:47 pm   #36
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Default Re: A TV set with mains EHT - in 1953!

Great stuff John,time to restore I think!
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Old 1st Aug 2020, 5:36 pm   #37
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Default Re: A TV set with mains EHT - in 1953!

Just out of interest it turns out that the massive HMV 1902B is in fact a London TRF receiver and it also retained it's mains EHT supply. It was released in April 1953.
This must be the very last TRF receiver built and almost certainly the last with mains EHT! If it works, don't fix it.
John.
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