[Catkins]

To continue the restoration...

As previously mentioned the state of the television was "upstairs - downstairs", every thing on the bottom of the cabinet was in a much worse state than (largely) anything which had been raised above the bottom.

Looking at the bottom of the cabinet there was clear evidence that rodents had been living in it, and there were pieces of newspaper dragged in for nests, and there was a large quantity of nibbled hazelnut shells and other unidentifiable organic matter deposits. The top of the power supply unit showed corrosion from acidic deposits. In general it was in a rather grimy state.

So far as I was concerned the first thing to do was take everything out, and disinfect the cabinet.

Photo 1 shows the cabinet with the contents removed and vacuumed out prior to disinfecting.

Once done I decided the first thing to tackle was the Power Supply Unit. That is first because it was in a worse condition than anything else, and I think it always best to know as soon as possible if any of the transformers (EHT especially) have failed due to damp (known as green spot due to corrosion of a winding producing a green spot at that point), which would mean they'd have to be re-wound.

Due to the condition of the Power Supply Unit I decided a complete strip down and rebuild, allowing everything to be cleaned treated and repolished, was essential. If there's any place where corrosion and deterioration isn't a good ideal it is where high power is involved.

Before I get onto the restoration proper, it is perhaps worth discussing the unique/unusual or otherwise features of this Power Supply Unit (for those that do not know already).

The Power Supply Unit supplies HT and heaters (filaments) to the TRF and Sync chassis (or the video signal amplification and timebase chassis in more general terminology), it also supplies EHT and heaters to the CRT. It does not supply power to the radio/sound chassis which has its own power supply unit (built into the chassis). This is obviously to allow the radio to run independently without powering the television chassis. Later generation EMI sets (like the HMV 904) have only two transformers, a combined radio/sound/vision transformer and a vision only transformer (which supplies the timebases and EHT). This is because the sound circuitry and video signal circuitry is largely shared. Which produces a substantial component reduction and cost reduction (at the expense of extra circuit switching).

There is nothing unusual electrically speaking about the chassis. One transformer supplies the HT and heater voltages (to TRF, Sync, and CRT, there are separate windings for the TRF and Sync chassis due to the load, there being a total of 14 valves). The HT voltage is full wave rectified and then goes through a reservoir capacitor and a smoothing choke and capacitor. The EHT is supplied via a separate transformer, and is half wave rectified, the output of the half-wave rectifier goes to the CRT chassis for smoothing and the essential bleader chain.

What is unusual (for the 1930s at least) is the attention played to preventing people coming into contact with the lethal EHT. The EHT transformer and rectifier is completely enclosed in a metal box. Additionally, the box comprises a EHT shut-off lever. This lever is normally compressed and placed in the off-position by the presence of the television back cover. If the back cover is removed, the lever will short EHT to earth. Such precautions are obviously because the designers were worried about people coming into contact with the lethal EHT.

Photo 2 is an original (i.e. when I got it) photo which shows the EHT enclosure with the EHT shut-off lever on the right.

The other slightly unusual aspect of this first generation set is it uses a large tag board for the power connections (one tag per connection). Later generation sets considerably simplified connection by using plugs and sockets.

Photo 3 is an original photo which shows the tag board, and its general condition when bought. Note on the left the heat-coil (a type of fuse) has been bypassed by some wire.

Photos 4 and 5 show the rusty state of the EHT enclosure, and of the chassis (with the EHT enclosure and EHT transformer removed and all surface dirt vacuumed and brushed off)