Page Six


Next I must join the extension wiring to the control panels at the other ends.

These panels will eventually be mounted at the side and back of the cabinet, so the leads have to be the right length.

The new video conversion and switching functions will be added later after I've got the basic TV set working satisfactorily in its new 'extended' form.


At this time I repair the damage to the screen bearing section, starting off with plastic wood.

The rest of the repair goes to plan and the end result proves satisfactory.


Now the control extensions are finished, I can hitch all the units up for testing on the workshop floor.

The black wire seen here, leading to a piece of foil tucked under a tube strap, is the new 'tube earth'. This part is easily overlooked but performs the vital function of earth return for the EHT smoothing. It is touching the aquadag tube coating.


Eventually I get all the units and their new control panels hitched up.

Next, to switch on.

First I run it up slowly on the workshop variac. I monitor the heater voltage across the tube for an indication of how hard the heater chain is being driven. The set is now being fed from the new mains isolating transformer, remember...


The picture appears but to start with is dim. It proves necessary to use the +15v 'boost' tap provided on the isolating transformer to restore correct mains voltage.

The picture is then back as it was. This is best described as 'early 50s mild' rather than 'late 50s brilliant'. I can think of one of my old customers who wouldn't be impressed! A better tube might improve matters, but there isn't one to hand.


Since this is to be a 'luxury' set, the sound will be as important as the vision.

It's time to try the separate valve amplifier I'm providing for the sound. This has much better bass response than the set's own audio output stage and as expected, 50Hz hum is now noticeable.

This is greatly reduced by bootstrapping the black capacitor shown onto the set's HT rail. The total capacitance now becomes 650uF !


The final wiring work is now done. This is to connect up the multiway wafer switch that will control the various input functions. Multiple screened leads converge here.

I shall have a choice between three types of input to feed this set, enabling it to work with a wide variety of sources.

I have obtained medication for my Parkinson's at last. This means I am now going like a bomb and the work is soon completed.


At this stage here's what the various gubbins looks like, taking up a big chunk of workshop floor. All this will later fit neatly inside the cabinet - I hope!


I switch on the set, along with all the new switchery. It works, but straight away I hit trouble.

The signal from the Domino converter is leaking through the switching and interfering with the view from the Aurora in both sound and vision.

Not only this, but their carrier frequencies are obviously slightly different, revealed by the presence of a new audio tone on the sound channel.


After working through various remedies, here's what I finally come up with. The section of the switch that handled the sound is now pressed into service to control the power into the Domino. This is shown in the blue block on the diagram.

'CNV' and 'MOD' relate to the conversion and modulator sections of the Domino standards converter. This old unit, which pre-dates the Aurora, will live inside the set where it will have the job of making a 405-line Channel 1 signal out of any 625-line baseband source that gets plugged in.

The sound (Aud in) is now connected directly, missing the switch. This doesn't matter since the bottom switch section already ensures no signal from the Domino, including the sound, can get through when the rig is operating in standard 'television aerial' mode.


The remedy does the trick. I can now try the rig on the output from my ancient VHS video recorder. Amazingly, after years of inactivity and a brief winding session on the tape, it works.

I can now start delving into my collection of vintage videos, recorded on both 625-lines and 405-lines in the 1980s. Now, at the flick of a switch on the back of this set, I can view all of them again.

On the screen appears the opening sequence from the film "Radio Parade of 1935", with singing telephone switchboard girls!

The picture is shown reflected in a mirror. The movement in the picture means it hasn't been very well captured here.


A top Radiocraft customer who has since become an old friend now comes to the rescue by donating a valuable and rare Mazda CRM123. This is a most generous gesture.

This tube has been rebuilt at some expense by RACS in France. It should physically fit the set because it's actually very similar to the Baird's original tube. So the Bush/Baird mix now becomes even greater.


There are some electrical differences between the (existing) Mullard and (to be fitted) Mazda tube, which will necessitate some preparation work to the chassis.

First the Mullard is a tetrode and the Mazda is a triode. There could be 'issues' with getting the Mazda to focus using the magnet intended for the Mullard. I just don't know yet how it will turn out...

Here is the base on the Mullard - a cut-down "British 12-pin" arrangement.


And here's the end of the Mazda with the base I have rustled up for it.

This is a Mazda Octal (MO). This was a British version of the International Octal (IO) type and it was not intended to be compatible. It has a larger central boss and spigot than the IO.

This base was first seen on British valves in about 1938. The earliest version of the tube I am about to fit first appeared in 1939. This is truly vintage technology.


This may be a CRM123, but being a RACS rebuilt tube, it doesn't have the original 2-volt heater. Instead, it is now 6.3 volt...

I don't know how much current it will draw and whether it will be suitable for hooking straight into the existing 0.3 amp heater chain on the set.

The only thing is to try it on a bench power supply. To my surprise, at 6.3 volts it takes as much as 0.6 amps. This is a heavier drain than I expected. Am I overloading it?


No, the colour looks about right at this current so 0.6 amps it will have to be! It's invisible at the (expected) 0.3 amps.

This will mean it won't hook into the existing heater chain and special powering arrangements will need to be made.