1936 Baird T5 TV Receiver restoration

It appears that the electronics need to be removed very soon or the cabinet will collapse.

Interesting that you mention about the full wave vision detector, I was reading the booklet in the attached link. The TV also uses a low IF and full wave detector and I didn’t know why. Question now answered and makes full sense.

It is an RCA document from 1939, an excellent read, I wish it would have been available or something similar when I was in my teens.

https://www.americanradiohistory.com/ARCHIVE-RCA/RCA-Review/RCA-Practical-Television.pdf

Hi Frank,

Full wave vision detectors were employed in Rediffusion  cable receivers.  Because the carrier frequencies were low,  for 405 lines BBC1 4.95Mc/s  and 8.45Mc/s for ITV there was a real possibility of a carrier dot pattern if a simple half wave video detector was used. I'd imagine that the British Relay Wireless cable TV receivers employed the full wave vision detector.

Bush made a TV receiver for Rediffusion and Top Rank  cable TV systems. Model TM100?

In the GEC BT8161 pre-war TV set the vision  IF frequency was only 4Mc/s and sound IF 500Kc/s so it was desirable to employ a full vision detector.  

Till Eulenspegel.

Yet we had the dot pattern with CTV, PAL being worse in this respect than NTSC due to the different offset.

Some sets did have a 4.43MHz rejector in the video circuit but that took a lump out of the video. Not that many viewers noticed or cared, it’s surprising what vision faults viewers will ignore.

Hi.

Nice project David. Regarding the FW vision detector the TFE & STFE front ends in British Relay viewing units did employ that way of detection, earlier sets with valve front ends didn't so the sets like the M17/3 & M19/11 didn't.

Hi Trevor,

The chassis assemblies look awful but in fact it's only surface rust and all the components are in good condition.

Worthy of discussion, perhaps elsewhere in the Forum is the regenerative sound demodulator employed in the later production model T5.  The FC4 octode operates in a mixer circuit, rather like the frequency changer in a radio receiver. The sound IF signal is supplied to signal grid 4 and grids 1 and 2 function as a 500Kc/s oscillator The audio output present at the anode requires filtering to remove the IF and 500Kc/s components before it is supplied to the audio amplifier.

The Baird T23 is a TRF receiver. Like the T5 model we are discussing the sound demodulator is very similar, except the signal grid of the valve receives the 41.5Mc/s signal. The oscillator operates at 500Kc/s as in the later T5. However, the Mullard FC4 will  not work in the T23. Instead, a Marconi-Osram MX40 pentagrid valve is used.   Unlike the FC4 the MX40 does not have a suppressor grid.

The attachment shows the position of the three chassis on the slide-out baseboard.

Till Eulenspiegel.

Meanwhile the set is disintegrating nicely, see the attachment.

Coming up soon, the scary business of removing that huge CRT.

Till Eulenspiegel.                                                                                                                                                                    

When I saw the first photos I was thinking is there enough wood left to support the electronics.

Hi Frank, 

the big problem is finding the correct walnut veneered plywood to do the cabinet rebuild. I'm phoning and emailing all the known secondhand furniture shops and wood recycling businesses around Newcastle and Gateshead.

The CRT is most likely a post-war replacement.  The original tube was the Cathodevisor 15MW1 and the tube fiited in this set is a 15MW4. Never come across this tube before.  So how do I remove the tube?

One idea is to place the set on it's side and withdraw the tube horizontally.  Or, in the manner as the tube was removed from the Baird T23, just lift it out vertically.  Whatever method, extraordinary care will have to be exercised handling this tube.

Till Eulenspiegel.

The general consensus is that the CRT should be lifted out vertically.  In order this can be done in a safe manner I've made a special cradle to keep the tube safe while it is out of the cabinet.

The plywood used to make the CRT cradle came from that Decca projection TV cabinet which many will remember was painted green. I still have the cabinet but that horrible green paint has been stripped off to expose a very nice walnut veneered  surfaces.

Till Eulenspiegel.

From the Early Television Foundation .  A Fernseh AG cathode ray tube which fitted in the companies' model DE6.  

http://www.earlytelevision.org/german_crt.html

Till Eulenspiegel.

It will be safe in its frame, the parrots will keep it company, 

Hi.

The infestation looks as bad if not worse than a certain HMV I had for a short while. David had done a fair bit to it including a base and radio panel. All was ok for a while then it all kicked off again. At that point it was passed on, I believe it may still be with Eric in Bishopbriggs. I don't relish handling that tube but the state of that cabinet means it must be seriously weakened. Let's hope that the tube is good and the whole job isn't a waste of time.

Three 2400mm X 1200mm sheets (8 x 4) sheets of plywood have been ordered, delivery today.

The 9mm sheet is top quality grade A and is to be used in the construction of the front and side panels. The 12mm and 15mm sheets are BB grade for the construction of the cabinet floor and chassis shelf.

But before any work can be done to the cabinet that CRT has to be lifted out.

Till Eulenspiegel.

Are you veneering the cabinet yourself? 

Hi Frank,  the 9mm plywood is furniture grade A and has a nice veneer pattern for the construction of the cabinet sides. The veneers for the front panel will be book matched in the same manner as the original.  There's also a lot of detailing to attend to on the front panel. The plywood sheets were delivered this morning. These will be cut into more convenient 1200 X 1200mm  panels for ease of handling.

Till Eulenspiegel.

Restoration work has restarted. A new shelf for the receiver and timebase chassis assemblies has been made. 15mm plywood is the material used to make this part. The first picture shows the panel marked out for various holes and the centre section which will be cut out for the CRT neck components. Before anymore work can be done to the cabinet the CRT will have to come and that's one part of the restoration I'm not looking forward to. The second picture shows the terrible condition of the original shelf.  

Till Eulenspiegel.

But before the CRT can be lifted out the screen aperture panel must be removed. This has been done and now I find that the panel is not in good condition because those nasty woodworms have been feasting on it.

So that's another part to be replicated.

Till Eulenspiegel.

There is so little good wood in that cabinet it’s surprising it’s not fallen apart with the weight of the electronics, must have been some fat woodworms.

Hi Frank,   

Only a few parts of the cabinet can be reused, the mirror lid can be saved but in reality this going to be a new cabinet.  The tube is ready to be taken out, lifted out vertically and placed on the special stand and then stored in a safe place well away from the workshop. 

Till Eulenspiegel.