With the Covid-19 restrictions curtailing our working weekends severely, it’s not been possible to make as much progress on our projects as we would normally manage.
That doesn’t mean to say that nothing is happening!
Pastiche Marconi equipment
Paul has extended his manufacturing of pastiche Marconi equipment, the latest items to roll off the production line are a valve amplifier for the production monitor speaker and an Aurora 625 to 405 line converter; both destined for Vivat. These are using metal cases which come from a Canadian company, once sprayed in Marconi colours they look quite good.
PWM picture tube
Vivat carries four MkIII picture and waveform monitors (PWMs), three for the cameras and one as an Engineering Manager’s monitor. We have a spare PWM chassis but it did not have a picture tube, this is a 10MW4 or 10FP4 type round tube and they are in short supply these days. Fortunately a contact in the USA (via an unrelated item on eBay) has supplied us with a suitable tube, it was expensive but was the only way we were going to get one.
It arrived very well packed and works well.
A cornucopia of connectors
Also via eBay we obtained what Paul calls a “cornucopia of connectors“. These will find a home in various places.
The equipment wiring in Vivat has been progressing slowly, using the video coax cable and crimp connectors kindly donated by Bryant Unlimited (who have now sadly closed due to retirement but have been reincarnated as several new companies). Some audio and communications wiring has also been completed.
Richard has supplied a set of spreadsheets detailing the various items of equipment and their interconnections; Paul and Dave have started converting these into a block diagram which helps to visualise the overall installation.
Sound mixer VU meter
The temporary sound mixer in Vivat had a problem with the large VU meter but Paul finally got to the source – faulty metal oxide rectifiers buried deep in the meter movement!
Vision mixer refurbishment
Refurbishment of the vision mixer from the Science Museum is continuing. The original switch banks had been modified by the addition of a diode switching matrix which was in poor condition both electrically and mechanically. As the modification is worthwhile, Paul has re-built it using new components on a suitable piece of stripboard.
Vivat carries a monoscope camera, this is a unit which uses a special tube to generate a test card or test pattern – a precursor to using logic or computers.
The unit we are using is working, after the usual replacement of faulty capacitors and valves, but the performance was not up to the usual standard. There were problems with the picture stability and black level which led us on a merry chase through the video amplifiers and clamp pulse generation circuits. It wasn’t helped by the fact that there are several different versions of the unit for different markets, plus there are different versions of the video amplifier system.
Eventually, after a lot of collective valve changing, component testing and head-scratching, we found that during an earlier refurbishment, by an unknown party, all the inter-stage coupling capacitors had been replaced with the same value instead of being different capacitance values depending on the circuit conditions. This was allowing through some low-frequency noise which caused the picture instability and affected the black level clamp.
Replacement of the various capacitors with the correct values according to the manual cheered things up no end!
Paul comments: “An interesting problem and an example of how modern thinking doesn’t always yield the result. All these monoscopes seem to do it and the designers ‘treated the symptom’ after removing as much of the disease as they could“.
Vehicle maintenance is also continuing, recently we checked and charged the batteries on Yorkshire Tyne-Tees, gave it some new diesel and managed to start it without too many problems. We also replaced a broken jubilee clip which was causing a water leak.
Once started, we moved it off the concrete pad so that we could clean the pad before returning YTTTV to it’s original position.
We also charged the battery in the horse box and it started first time! This is required for two reasons – for transporting Jill’s horses (of course) and also because it is blocking the entrance to the storage for Vivat and Southern! The next job is to start Vivat and back it out of the storage.