This evening the CRT was removed from the cabinet. A real scary job.
The tube now rests on the special receptacle that was made for this restoration project. The CRT has a thick neck, 45.5mm, much thicker than the Cossor tube installed in my Baird T23.
Now the dismantling of the cabinet can begin.
Till Eulenspiegel
Well done to you David.
Look at the woodworm...... unreal.
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
Todays pictures show the dismantled cabinet. The construction of the cabinet floor will one of the easier tasks. A piece of 15mm plywood will be cut to 24 X 16". Also required a 15mm thick solid wood batten 24" X 2". The latter part forms the lower rear edge of the cabinet.
The third picture shows all that is left of the rotten cabinet floor.
Till Eulenspiegel.
One of the easier jobs, the cabinet floor.
Till Eulenspiegel.
This job wasn't so easy. The replacement focus coil support. Two attempts to get this one right. Problems cutting out the 4" diameter hole.
Till Eulenspiegel.
What happened, did it split ? Nevertheless a perfect second attempt.
Frank
Hi Frank, for the first attempt the 4" hole saw was tried out in the pillar drill. It was found to be impossible to make a perfect cut, ragged edges, no use at all because I want this restoration to be perfect.
For the second attempt the hole saw was fitted in the hand held power drill. Lubricating the hole saw with linseed oil helped matters.
Till Eulenspiegel.
This is what I call a real restoration. In the true sense of the word, a vintage set is returning to it's former glory before our very eye's.
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Andrew and Mike,
many thanks for those kind comments. Coming up this week will be the construction of the shelf that supports the CRT. This is going to be another tricky job. At first sight the panel looks simple enough. However, there are four slots cut out in the panel which are in the form of 50mm arcs. These are for the adjustment of the pole pieces that extend out from the frame oscillator transformer.
The Baird T5 employs a single valve frame oscillator, a better description is a power oscillator. The valve is the Cossor 41MP triode. https://www.radiomuseum.org/tubes/tube_41mp.html The same type of valve is employed in the self-oscillating line output stage.
Till Eulenspiegel.
The reverse side of the CRT panel showing the frame oscillator transformer. Note the pole pieces that extend from the transformer. This method of frame deflection was used on all pre-war Baird TV sets. The post-war "Theatreland" Baird TV sets employed a similar arrangement. Also early Ambassador sets, models TV1 and TV2.
Till Eulenspiegel.
Today the construction of the new CRT support board was completed. The frame oscillator transformer test fitted. As the panel appeared to be in better condition when compared with most of the other wooden parts in this set I did consider restoring it, but abandoned that idea when it started to disintegrate. One corner of the panel is badly damaged. The third picture shows all the new parts made so far and the serviceable items including the CRT.
Coming up next: the loudspeaker baffle. The energised loudspeaker is in good condition.
Till Eulenspiegel.
Will there be anything else left of the old cabinet, the new wood work is first class?
Frank
Hi Frank, the truth is very few parts of the original cabinet will be reused. The cabinet mirror lid can be saved, the wood worms have shown no interest in that part of the set. The internal hard wood battens can be reused but will receive woodworm treatment as a precaution. The HMV 900 cabinet I worked on way back in 2011 was in a bad state but this Baird set is worst set I've ever seen. Although, the HMV 1804 I acquired in 2017 is pretty bad, but at least it's solid. The Baird was in a state of progressive disintegration. When the cabinet is reassembled with it's new parts it will be a solid structure again. The attachment shows the HMV 1804.
Till Eulenspiegel.
Today the loudspeaker baffle was removed. As the attached picture shows it's in a terrible state. A replacement baffle is being made. It should be finished tomorrow.
Till Eulenspiegel.
The new loudspeaker baffle.
Coming up: the front of the set consists of three plywood panels. Tomorrow I will make a start on the middle section. See pictures 2 and 3.
Till Eulenspiegel.
I reckon we can call you the Wizard of Wood ?
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Andrew, it's fortunate that nowadays reasonably priced tools are available. Imagine attempting something like this restoration job forty years ago! One tool I had to search for is the 15 degree router bit which will be used to cut out the chamfered edges in the CRT support panels. It will also be needed when it comes making the cabinet top panel. The CRT screen aperture also has chamfered edges.
Till Eulenspiegel.
This week the cabinet outer panels will receive attention, the side panels should be easy to replicate, 9mm plywood will used for the construction of these. The front of the cabinet consists of three parts. The upper panel has the user controls, the middle section has the loudspeaker aperture and the much larger lower section has the door which conceals the pre-set controls. The middle section has already been removed for inspection and like all the other plywood panels it is useless, completely rotten. So this is the next part to be replicated. 12mm plywood will be used to replace the original 1/2" thick plywood panel.
However, there is a possibility that the main front panel section can be saved, it is quite solid. There is evidence of woodworm activity but it is no way as bad as the internal plywood parts. The panel could be treated with woodworm fluid. The worm holes filled and the outer surface re-veneered. The internal hardwood framework certainly can be retained as it seems the woodworms have gone for the easy to penetrate plywood sections.
Testing the sound receiver. Using a borrowed power supplier set to provide 250 volts HT and 4 volts for the valve heaters. The audio amplifier consists of a Mullard 354V triode and a Mullard PENA4 output valve. That part of the circuit is working OK and there is some activity when the top caps of the FC4 detector and TSP4 IF amplifier valves are touched. All the B & I make capacitors are leaky and will have to be restuffed. The loudspeaker is of the energised type and is mounted on the new baffle board.
The audio demodulator is worthy of discussion. The FC4 octode grids 1 and 2 functions as a 500Kc/s oscillator. The sound IF signal is supplied to grid 4. Internally connected grids 3 and 5 are the screen grids. The resultant audio signal is developed across the anode load resistor and supplied after filtering to the grid of the 354V audio amplifier triode. A similar circuit is used in the TRF model T23. The FC4 is replaced by an Marconi-Osram MX40 pentagrid mixer valve.
Till Eulenspiegel.
A new loudspeaker panel has been made. After several attempts at making the new panel a perfect fit I can sign off this stage of the cabinet restoration. Now a decision on what to do with that front panel. Should I restore it or make a replacement? There's still a possibility that some nasties exist in the eighty year old plywood. You have to be ruthless when it comes to dealing with woodworm infestation. Any doubt cut it out! The first picture shows that the original loudspeaker panel has disintegrated as a result of woodworm damage.
Till Eulenspiegel.
Correction to my last post. The loudspeaker should be sited on the left side of the front panel.
Till Eulenspiegel
