Page Five


At this time I decide to take a look at whether the DC component of the vision signal can be better preserved. This is to ensure the picture doesn't 'grey out' in dark picture scenes, as was often the case with the AC video coupling found in many black-and-white sets. The only advantage of AC coupling was that it showed up aircraft flutter less severely, but that won't be an issue today with the signal being obtained from an Aurora.

The blue shows the existing signal path from the video output to the tube. It turns out I have nothing to do! It is DC coupled already... C25 just adds some high frequency lift. I now try disconnecting this capacitor and the picture actually improves. This allows me to disconnect the wire 'bodge' added earlier to the vision IF output.


Earlier on I mentioned how I would like this set to accept not only Channel 1, but also baseband video (on both 625 and 405 lines) and sound. This will enable me to view my old collection of VHS 625 and 405 tapes at the flick of a switch.

Everything will be displayed at 405-lines on the screen.

I wanted there to be no inconvenient re-plugging involved so have come up with this system. I was lucky enough to find a 4-pole 3-way wafer switch in my stock. The whole thing rather depends on this.

The 'CNV' and 'MOD' refer to the functions of my old 'Domino' standards converter which, for years hadn't been doing very much. It was superseded by the 'Aurora'.


Here is the Domino on its side. It is to be permanently mounted inside the set to handle the 625-to-405 conversion (when needed). This is effected by adding a central mounting bolt which, with a nut, will secure the unit to the cabinet floor.


The new system selection controls will replace these two cardboard panels Actually this is one piece of cardboard mounted behind two orifices.


This new aluminium panel will replace the cardboard, mounted behind the two orifices. I made this up from two smaller pieces of aluminium I had to hand.

The holes, from left to right, will take the Ch1 aerial input, the video and audio inputs, the system selector switch, and - on the right panel - the timebase amplitude and hold controls.

It will of course be earthed.

The AC/DC set chassis will be powered through a new isolation transformer. There will be a true earth reference adopted throughout the system.


I now prepare the mounts of all the various units. Here the cabinet is placed on its side while a thickening MDF panel is glued in, weighed down by a couple of lead acid batteries!

This thickening panel is needed to take one of the new mounts of the Bush TV chassis...


... which sits on the floor to the right - next to the other gubbins. There is plenty of room in the Baird console cabinet - all wasted in the original set!


Unfortunately during the test fitment I lose my balance (thank you Parkinsons!) and fall against the TV screen unit standing on the floor nearby.

I badly jolt the tube, but this appears to have survived. The upshot is this scratch, which will have to be later repaired.


Previously I had constructed this bearer from timber to hold the rear of the tube.

There's no Baird chassis there now to do this job!


This pot in the RF/IF tray is used to control the vision interference limiter. Under modern closed circuit conditions it will become redundant, so it is now removed.

Doing this will also take a little of the load off the HT.


Attention now turns back to the cabinet.

I want to improve the appearance of the speaker grille, which in the Baird was expanded metal.

Here, some fine nylon netting is being soaked in hot coffee to make its colour a little warmer. What we can actually see is the round inverted plate used to hold it down in the bowl...


A layer of the netting is then applied over the original expanded metal...


... then a second layer! All this is held together with Scotch spray adhesive - the can is seen at the top.

The effect is like a vintage speaker fabric. The real thing sadly now seems to be unavailable.

The speaker board is now mounted back in the cabinet behind the wood spars.



Back now to the electronics, and the scan coil leads are extended so they will reach the chassis in its new home at the bottom of the cabinet.

The EHT lead, tube base leads and tube earth are extended too.


Time to consider the powering arrangements. The various units are all to be powered through this isolating transformer and earthed.

This feeds a distribution block, into which the units will be plugged.


The tangle of new extension wiring is getting a mite confusing on the bench!