Re: Baird Garrick
Hi all,
so the saga of the radio section of the Baird continues.
One of the issues was that the original drop though mains transformer had been replaced with an enclosed chassis mounting type which also produced HT which was 100V too high!
First I took one of the end covers, cut its legs of and made a slot for the voltage ajustment panel.
Then I unwound the secondaries of the transformer. With a drop through transformer we need all the wires to come from one side of the windings, ie. we cannot have wires that have to run past the lamminations. One way of doing this would be to rewind the primary with the wires emerging at the correct point. However, I decided to take the easier route of fitting a couple of wires to take the live and neutral connections round to the other side of the transformer. To do this I had to drill some extra holes in the coil former without damaging the primary winding and a strip board track cutter proved perfect for this.
The transformer, accounting for load worked out at 6 turns per volt, so 1500 turns of 36 SWG wire were wound for each half of the HT winding. Then 30 turns of 18 SWG for the rectifier heater, followed by 38 turns of 19 SWG for the 6.3V heater supplies.
I painted the top cover and cut some Nomex paper to insulate around the voltage selector.
With the transformer back in place the chassis is looking much more like it should do. The HT is now correct at 250V DC.
Extra hum and occasional bright purple fireworks with spectacular yellow sparks flying off its cathodes pointed to a very unhappy 5Z4G. A replacement restored reliable operation of the radio.
Hum was still a problem with the TV sound though and this was traced to a poor connection between the chassis and a solder tag which provides the ground return for HT, Heaters and audio from the TV sound unit. I added a wire from the tag straight to the grounding point of the 6.3V heater winding from the mains transformer and that cured the problem.
The next thing is to make a cover plate to blank off the holes in the chassis where the mains adjustment had once been fitted. I also need to re-align the TV sound unit.
In other news, I now have some lovely 9mm playwood for the back panel and have made a template from another collector's Bair Lyric. The two cabinet styles are very similar in overall height and width, but the chassis' are mounted at a different height to my set, so a little more work is needed to establish where everything goes.
That's all for now. Plodding on slowly, plod, plod...
Cheers
Andy
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