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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 8th Feb 2006, 11:46 pm   #1
FERNSEH
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Default Pre-War vision modulator. The London transmitter.

I have some information on the modulator system employed in the Marconi-EMI pre-war transmitter.
The modulator consists of four stages: The line amplifier, the sub-sub modulator, the sub modulator and final stage the modulator proper.
The first three stages are essentially amplifiers. The line amplifier accepts the video from the control room and uses two parallel E708 pentodes as the amplifier and two more E708s as the cathode follower.
The next stage, the sub-sub modulator has a single DA100 triode as the amplifier and two parallel DA100s as the cathode follower. There is no mention of the HT voltage supply to this stage but I guess it must be more than 1000 volts.
In the sub modulator things get big. A DEM3 triode is the amplifier and two parallel DEM3s serve as the cathode follower. The video ouput from this stage is 600 volts peak to peak.

The modulator employes water cooled valves. The modulator valve is a CAM3 and the cathode follower is a CAT6. The modulated video video output is 2000 volts P-P. The cathode follower supplies the final amplifiers, two CAT9s
Again there is no mention of the HT supplies but there is no doubt the voltages must be into many thousands.

DFWB
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Old 9th Feb 2006, 1:44 am   #2
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Default Re: Pre-War vision modulator. The London transmitter.

As a follow up to my last essay about the pre-war London transmitter. There is plenty of information about the Marconi-EMI vision transmitter, but what about the Baird vision transmitter? I do know that in order to circumvent Marconi patents the final amplifier employed a single Metro-Vickers tetrode valve. But that's all.

DFWB
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Old 9th Feb 2006, 11:35 pm   #3
Danny
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Default Re: Pre-War vision modulator. The London transmitter.

Hi ok then all we need is the curcuit and some water cooled valves Oh no we are going to have a water shortage (ok i will go and do something usfull)
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Old 10th Feb 2006, 1:56 am   #4
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Default Re: Pre-War vision modulator. The London transmitter.

Hi Danny,
I've got the circuit of the AP modulator. but those water cooled valves could be hard to find these days.
Water supply is no problem in the North-East of England to cool the valves.

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