This is the only known surviving Pye monitor of the type that was originally installed in MCR21. This example was made in late 1963, so could have been in one of the MCRs, or installed elsewhere. There is no record of it’s use. It is serial number 130.
Controls:- H. position, H. width, H. hold, AC on, Brightness, Focus, Contrast, I/P 1 or 2, Sync int/ext, V. height, V. Centre
The monitor rear with 2 inputs & Ext. Sync. Additionally there is a third auxiliary test video input which produces a negative image and is added to the other selected input. If it was fed with “grille” it could be used for adjusting camera scan linearity.
The top left switch is B+ on/off and next to it, Hor. Osc trig/AFC
In many respects the monitor is nicely made with front and rear castings. Whilst it is the same size as it’s predecessor the build is quite different. It has excellent accessibility with fold down chassis that unplug for quick replacement. All pre-set controls are clearly marked and the individual components have their part number on them.
Chassis Left to right: PSU regulator, Field scan, Video amplifier.
This is other side with the sync separator and EHT units. The monitor has and independent EHT section and in this monitor it has given trouble and is in a poor state. The oscillator valve is a EL360 pentode, the transformer is arranged as a tripler with 3 QU37A rectifiers. The regulation is done by a shunt stabilizer valve type A2637.
The line scan is by another EL360 valve. The monitor auto-senses the input line standard and switches automatically.
This is next model that Pye made just 3 years later, apart from the two EHT rectifiers it is all solid state. It has the same screen size as the original monitors and is simliar in function. We do have the correct number of these and we plan to use them in place of the 842822 monitors.
The rear of the monitor has very clean lines with only the mains transformer protruding. The red “dot” is an overload trip, above it is the 405/525/625L standards change switch. Unlike the 842822 it is not auto sensing for line standard.
The inside is nicely laid out with a large PCB on either side. Line and PSU on the near PCB and the video amplifier and frame scan on the far one. In the centre section there is a diecast aluminium box with the free running regulated EHT generator. It has a voltage doubler with two EY87 valves.
The accessibility to the two main PCBs for maintenance is good and the EHT unit can be accessed from below by removing just eight screws.
This monitor is in working order and and ready for installation.
It was last serviced in 2014. For monitors that are now over half a century old!! the reliability is good, once a modicum of work is done on known problem areas. It is hoped that we will be able to keep these monitors working well into the future provided spare CRTs type M36-12W & M43-12W can be found.
This monitor is to be installed in Zone 1 the front engineering area, up above the maintenance bench. It is connected to the engineering output of the preview matrix via the Tek 515 oscilloscope which was used as the waveform monitor.
I was there – it was known as “Operation Vague One” and involved the RAF participation in the repatriation of the body of the Duke of Windsor to England. I think that the actual date of the live event was 31/5/1972. https://youtu.be/Eurv2p8TvdQI have no idea whether the pictures in the YouTube link are those from Lo21. The Duke of Windsor was formerly Edward VIII, King of the UK and Emperor of India from 20th Jan 1936 until his abdication on 11th Dec of the same year. He died on 28th May 1972 in Paris, so the 29th would fit in with a rapid deployment of Lo21 to RAF Benson.