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Old 31st Dec 2005, 4:39 am   #1
earlytv
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Default EHT rectifier valves for early TV kits

In 36 when your TV was up and running, over here we had some kits
and some HAM radio opps played with TV. I am trying to build one of those
KITS but find only the 878 HV tube for 7000v anode supply for CRT.
The 878 in a large chunk of glass. Did you have other tubes for a line
HV supply with about 7000v out and 15000 peak inverse?
I found tubes such as 1B3 were not meant to have 50 or 60 cycle power, they
were meant for flyback use only?

Thanks

Dennis
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Old 31st Dec 2005, 1:01 pm   #2
Duke_Nukem
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Default Re: HV tube

The SU2150 is found in a number of pre-war tellies over here, as well as in a number of ‘scopes. The Cossor 1210 uses this valve to rectify 4.5KV mains to produce 5.6KV of E.H.T.

The M*zd* U22 is used in the immediate post war Philco A1707 and that generates an EHT of around 5800V.

The SU2150 is large valve – with almost nothing in it ! Weenie lil’ EHT rectifier valves didn’t appear ‘til around 1948, they were designed specifically for use in tellies as flyback rectifiers. Although I guess arrangements could be made to run their heaters from 50Hz/60Hz I think there are several performance issues in doing so. This is supported by the fact that several technically backwards manufacturers (such as HMV) were still using mains EHT as late as 1950, several years after valves such as the EY51 had appeared yet they still resorted to a U33 valve, producing a feeble 4.9KV EHT.

I'm afraid a quick search of some example sets failed to find anything pre-war with EHT approaching 7KV.

TTFN,
Jon
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Old 31st Dec 2005, 2:21 pm   #3
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Default Re: HV tube

On the net found a sheet on the U33. Said it could handle 6.3KV RMS and that could give 7kv at low current?
Where can one buy a U33?
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Old 31st Dec 2005, 2:57 pm   #4
Duke_Nukem
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Default Re: HV tube

Hi Dennis,

I don't know about the USA, but there are a list of UK supplies (many with websites) here :-

www.vintage-radio.com/contacts/suppliers.html

The U33 sounds familiar so I don't think it'll be difficult to source.

Do you really need 7KV ? This is quite high for pre-war sets. And of course if you wan't the real pre-war TV experience then you don't want the picture to be too bright

TTFN,
Jon
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Old 31st Dec 2005, 7:52 pm   #5
earlytv
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Default Re: HV tube

Thanks for the help!
CRT I wanted to use was 9 inch round 40 degree deflection angle.
Only CRTs listed were 9AP4 and RCA 1800 series for Ham radio opps
to use. Neither one of those are around anymore. I did find a supply
of almost 9 inch (8.40) 40 degree CRTs that looked like 1800 series.
I have 1st CRT at rebuilder to change screen phosphor, gun and socket.
It will look like a 30s CRT but is way newer than that.
I had them aluminize the screen and that takes a higher anode voltage to work.
TV will use early USA standards of 120, 240, 300 non interlaced lines.
Vert rate = 24. I have a scan converter for all but 300 lines.
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Old 1st Jan 2006, 5:19 pm   #6
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Default Re: HV tube

Hello,
Very interesting comments. Around 5kv should give a very good picture on a 9" aluminized tube. The post war HMV set using the U33 is the 1805 series,an example of which I have in my collection. The U33 is the post war version of the U16 used in the first generation 1936 models and the two are interchangeable. 5kv produced a super bright picture on the Emiscope TA10 10" tube and its big brother the 15" version TA15. The brillaince has to be seen to be believed! As Jon says. I also have scanned the pre war data and cannot find anything over 5kv due I think to the difficulty in winding mains transformers to that specification. A few very rare projection models used voltage doubling technique but this must have been a fire hazard to say the least! Good luck with your project. Regards. JOHN.
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Old 1st Jan 2006, 5:40 pm   #7
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Default Re: HV tube

Quote:
Originally Posted by earlytv
Thanks for the help!
CRT I wanted to use was 9 inch round 40 degree deflection angle.
Only CRTs listed were 9AP4 and RCA 1800 series for Ham radio opps
to use. Neither one of those are around anymore. I did find a supply
of almost 9 inch (8.40) 40 degree CRTs that looked like 1800 series.
I have 1st CRT at rebuilder to change screen phosphor, gun and socket.
Hi,
I am interested in this rebuilder. Please can you give me his phone number?

Kind regards
Darius
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Last edited by Paul Stenning; 1st Jan 2006 at 5:46 pm.
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Old 1st Jan 2006, 10:05 pm   #8
Ed_Dinning
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Default Re: HV tube

Hi Gents, on the question of EHT voltages, it is unusual to see them over 6KV as this is the limit for an air insulated transformer, even at this voltage they need special precautions and are not that reliable even with modern insulating materials. Above this voltage they are usually in an oil bath.

Ed
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Old 2nd Jan 2006, 1:52 am   #9
earlytv
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Default Re: HV tube

I was all ready to go with about 5KV but rebuilder said that was a little
low. The 2 transformers I have, 1 4kv rms 1 6kv rms, are bare neon
transformers. Each coil is on its own thick plastic form and has been dipped
in a clear very solid ?? Then the metal core is put in and around. They were
made to put out 20 milliamps for neon bulb array. There is much room
from out side of coil to metal core, enough room to take 30KV anode lead
and wrap it around primary to make a filament winding for the U33.
To rebuild the CRT, new screen phosphor and gun, cost about $350.00 US.
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