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Old 29th Apr 2018, 10:26 pm   #21
beery
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Default Re: Baird Garrick

Hi all,
Here is the TV sound section of the Baird.

There are no waxies in the sound section, so a quick clean up with an oil soaked scouring pad was all that was needed.
This chassis is made of tin plate, so I had to be gentle with it. I did not want to use rust converter or anything like that as I am mindful of not wanting to mess anything up, given that there is no service info available.
I also fitted the missing valves and a sensitivity control knob. The original style knob is probably impossible to find, but as it is an internal control I'm not too bothered.

I've not needed to draw out the circuit for this at present. Hopefully I won't need to revisit this chassis, although it is very easy to get to. I will however change the cable mounted octal plug that is fitted to this chassis as soon as I get hold of one as the locating spigot is missing.

The TV sound output is stage is located in and shared with the radio section, so this is my next area of focus as well as the TV PSU as both have parts that require painting.

Cheers
Andy
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Old 10th May 2018, 12:48 am   #22
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Default Re: Baird Garrick

Hi All,
I've now gutted and re-stuffed the electrolytics from the TV PSU and the radio chassis.
I used 10uF film capacitors to replace the original 8uF sections in the TV PSU. I would not normally use these as they are much more expensive than electrolytics, but I managed to obtain quite a number of them from old high quality fluorescent lighting balasts that were being thown out at work.

The second photo shows the capacitors glued back together with epoxy resin and temporarily held together with tape whilst the glue sets.

Cheers
Andy
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Old 11th May 2018, 8:42 pm   #23
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Default Re: Baird Garrick

Hi all,
I've now put the PSU back together.

When I initially drew out the circuit, I found that two resistors in series were providing a link between the timebase HT and vision strip HT. Originally one resistor would have been used, but presumably the original burnt out. Of the two that were fitted one was also burnt out and the printed value was burnt off too.
I suspect that there will be a leaky wax decoupling cap in the vision section that caused the overload in both cases.
The outer ceramic covering of the burnt out resistor was removed so that a good section could be measured to work out the aproximate value. It worked out to be 1.2K to 1.3K ohms, which with the other resistor of 330 ohms works out to be a 1.5K resistor aproximatley.

A new 1.5K 14W resistor was fitted and positioned slightly further away from the wiring than the previous two in order to protect the insulation of the transfomer wires which were slightly burnt when the resistor originally failed.

The second and third photos show the before and after of the underside of the PSU. I refered to the earlier photo when re-fitting the electrolytics so that they were rotated round exactly the same way in their clamps.

The fourth photo shows the top view of the PSU. The transformer now looks a little bit untidy next to the newly painted smoothing choke. I might paint it in situ at a later date, but for now I must focus back on the radio section.
I've not tested the whole PSU yet as I need to attach a load to it first. I have tested the transformer though and it runs nice and cool.

Refitting the mains EHT is a job for much later, it can wait for now, but I am accumulating the necessary parts.

Cheers
Andy
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Old 12th May 2018, 10:18 am   #24
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Default Re: Baird Garrick

I came into telly bashing in the 80's working on broadcast monitors so the circuits involving valves etc are a compete mystery to me!

Just wanted to say how much I am enjoying your restoration, I hope it won't sound too condescending to say I admire your ingenuity and your 'cunning' methods to disguise new parts as old parts! I only wish I understood the technical descriptions of how the circuits work.

Really enjoying your updates and I'm looking forward to seeing the final set with pictures (and maybe sound via youtube?).
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Old 12th May 2018, 12:55 pm   #25
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Default Re: Baird Garrick

I'll remember your technique of measuring what's left of a burnt-out resistor. Wouldn't have occurred to me, but potentially very useful!
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Old 22nd May 2018, 1:13 pm   #26
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Default Re: Baird Garrick

Hi everyone,
thanks for the messages of encouragement. This is quite a long slog, but it keeps me out of mischief.

Remember the mouse eaten speaker? I've included a photo of the front of it just to show how bad it was.
I managed to obtain a period speaker from ebay which thankfully had a mounting point for an output transformer.
The output transformer was removed from the original speaker, but is was too big for the mounting on the new one, so instead I fitted a transformer recovered from a pre-war HMV radio.
The speaker has now been fitted to the set and it looks like it has always been there

The radio unit is slowly going back together, it still need its waxies replaced, but I may do this one at a time due to there being no circuit diagram available.

Cheers
Andy
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Old 22nd May 2018, 10:09 pm   #27
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Default Re: Baird Garrick

Watching intently, Andy. I was one of no doubt many who was tempted to buy this then chickened out in deference to some higher being.
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Old 8th Jun 2018, 2:18 pm   #28
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Default Re: Baird Garrick

Hi all,
progress has been slow and some of my time has been spent winding prototype switched mode (flyback) transformers for work.

The photos show the initial condition of the radio section, although I've added a few valves in this photo.

The next two pictures show the cleaning of the chassis.

The fourth photo shows the current state of the underside of the chassis, with most of the waxies rebuilt and temporary electrolytics tacked in.

On power up the HT rail was found to be about 100V to high, this is due to the mains transformer having been replaced in the past with one that does meet the original spec. I've now added a 1.5K resistor in the smoothing circuit to compensate for this for now. I'm looking to rewind or replace this transformer.
The radio showed signs of life on MW, but SW turned out to be very deaf. However this may not be a fault as it is hard to pick up any radio in Ware. I will check the alignment though.
I also tried the TV sound section and it works, though again, not very sensitive, but this is unrelated to the SW insensitivity.

I'm planning to have a look at another set this weekend to take some measurements and see how the back panel is made, as well as have a look at the EHT section.

Cheers
Andy
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Old 29th Jun 2018, 11:37 pm   #29
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Default Re: Baird Garrick

Hi all,
Yes, slow progress on the Baird again.

I was able to pay a visit to another TV collector who has the only working example of one of these sets that I know of, though his is actually a Lyric, which uses the same chassis. It worked quite well acutally
By taking some measurements on the working set I was able to ascertain that the non-original mains transformer in the radio section is indeed giving out too many volts, so I will have to replace it.

I've attached a photo of one of the smaller electrolytics from the radio chassis. These capacitors are hard to restuff especially when (as in the case of this capacitor) they are not held in place with a clamp. The only option seems to be to cut the capacitor length ways, though this means they never go back together properly. Anyway, you still can't see it when the capacitor is back in its original position.
I have now rebuilt all the capacitors in the radio section. One thing I found along the way is the poor standard of construction. Whilst all the solder joints are good, none of them are properly mechanically secured. Where wires and components join to solder tags they don't pass through the tag eyes, but are merely pushed against the side of the solder tag

I had to replace the smoothing choke in the radio section as I have taken the original to form the line output transformer. The original choke was 10H 170 ohms which is overkill, but it was really designed for the TV PSU which has an identical choke.
A replacement choke was given to me, but it measured 3H 68ohms. I wanted at least 5 henries and something nearer the right resistance. I unwound it and found it had 2080 turns of 31 SWG wire. Experience led me to pick two sizes smaller, so I filled the former up with 33 SWG, of which I managed to fit 3250 turns, which came out to 6H 155 ohms. In order to measure the inductance the core has to be reassembled together with the core gapping paper.
After putting the choke together I decided I really needed to clean and paint its rusty U clamp, so until the paint hardens I can't try it.

I now need to look at the problem of the mains transformer, before I try to solve the problem of mains hum on 405 line sound. The hum is not helped by the fact that the set does not switch off the audio when switching between radio and TV, it merely switches the heater supplies over from the radio RF/IF to the TV sound receiver.

I've removed the vision reciver from the TV section and this revealed yet more mouse droppings It also showed up a mystery, a missing valve which I assumed is an SP41 has a grounded top cap or grid, very odd.

I've also included a nice photo of the position of the contrast control. Not only have you got to remove the back and run the set with its nasty exposed mains EHT (more on that when I get an EHT transformer for it), but you have to reach right in and run the risk of breaking the CRT vacuum pip when adjusting it So why put it there, why not put the pot shaft sticking out of the rear of the chassis?? Answers on a postcard please.

That's all for now.

Cheers
Andy
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Old 2nd Jul 2018, 9:22 am   #30
mark pirate
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Default Re: Baird Garrick

Quote:
I've also included a nice photo of the position of the contrast control. Not only have you got to remove the back and run the set with its nasty exposed mains EHT
That is utter madness, at least the pot could have been fitted to the rear end of the chassis?
I have to agree about the poor build quality of Baird sets, My T164 is no where near the quality of it's peers of the time, but apart from the very poor CRM92, performs quite well.

Mark
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Old 2nd Jul 2018, 8:24 pm   #31
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Quote:
I have to agree about the poor build quality of Baird sets
With my Baird Townsman, I gave up - and installed a Bush TV24A chassis. A great improvement.


Steve
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Old 1st Aug 2018, 11:12 pm   #32
beery
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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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Old 2nd Aug 2018, 12:11 am   #33
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Hi all,
I've just noticed I said 'playwood', well I don't know what that is, maybe it is a bit like plywood, but more fun. BTW 9mm plywood for a back panel is plain bonkers of course, what was wrong with a bit of cardboard?

Cheers
Andy

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Old 2nd Aug 2018, 8:11 am   #34
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Default Re: Baird Garrick

Yes! My old Gran would have said 'All show and no knickers'. Crazy overspend on the cabinet and a load of rubbish inside.
HMV did the same thing with the 1807. John.
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Old 14th Aug 2018, 7:52 am   #35
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Thanks for the encouragement John.

So, much like my crazy overspend on a valveless cabinet and a load of mouse inside then...

Sometimes external events influence the order in which a project progresses and indeed this is what is now happening here, in a good way though

A week's visit to my parents place provided the opportunity to use the vice mounted folding tool to make up the supporting bracket for the EHT rectifier.

First folded to shape, drilled and then a q-max cutter was used to make the hole for the valve socket. Finally the top radius was added and then a check to see what it looks like in the set. Yes folks the EHT capacitor does sit off the edge of the chassis (the original cap was even bigger!) and yes the entire bracket is at EHT potential

Now back home, but with my wife and daughter at my parents for another week I can do some noisy bits (my daughter's room is above my work room), so work on the cabinet back has now started.

Cheers
Andy
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Old 14th Aug 2018, 9:04 pm   #36
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Default Re: Baird Garrick

Hi Andy
I like that vice mounted bending jig , very useful bit of kit.
Keep up the good work.

Robin
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Old 4th Sep 2018, 3:38 pm   #37
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Hi all,
an update on the Baird.

I drew out the circuit of the TV sound section (attached). Notice the inefficient capacitor coupling between stages. Also the aerial input coil needs to be terminated with load of the aerial input of the vision section in order to work properly.

The TV sound section was unstable at high gain. I found that C4 was missing and that R7 had been replaced with 100 ohm and 150 ohm resistors in series. The remains of C4 could be seen soldered to the chassis, so I found suitable vintage parts and fitted them. The sound TRF unit is nice and stable now.

I made a small aluminium plate to cover the hole that had been left by moving the mains voltage selector. I also replaced the 50s double insulated mains input cable with a twisted pair of blue and black wires as it would have had originally.

The back cover of the set has now been drilled and routed and the brass screw cup inserts have been fitted. The mains input hole needs to be filed into a slot and the CRT neck box needs to be assembled.
The rear controls do not extend as far as the back panel, so it is a case of having to stir around the controls with your fingers! To make things more interesting the identity of the rear controls are not marked on the rear panels of the other sets I have seen.

That's all for now.

Cheers
Andy
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Old 5th Sep 2018, 12:39 pm   #38
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Default Re: Baird Garrick

Hi Andy,
That's a very nice back you have made for the Garrick cabinet. I'd image that the CRT neck protection box will be made from wood also.

Will it be painted black or simply left in the condition it is now?

Excellent circuit diagram of the sound RF amplifier and demodulator. Audio output is positive going so no possibility of AVC. Note the simple noise limiter, clips the positive going spikes.

DFWB.
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Old 5th Sep 2018, 4:11 pm   #39
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Hi David,
thanks for the comments. I've attached the only picture I have of a Garrick back. The back on the Lyric that I have been using as a reference has a slightly different back because the timebase chassis and radio sections are at different heights in the cabinet compared to the Garrick.

So, yes the neck box is also wood and the whole lot will be painted black

Cheers
Andy
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Old 7th Sep 2018, 1:29 am   #40
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Hi all,
I've attached a photo of a Baird Lyric back as reference for the kind of thing I am aiming for with the replacement back panel for the Garrick.

The vision RF unit has now been cleaned up ready for evaluation. One photo shows what a couple of the heater decoupling capacitors looked like after cleaning, to the right of them you can just make out the two that still needed cleaning.
The last photo shows the finished look after rubbing down with an oil soaked scouring pad.

The cleaning of the RF unit involved and unpleasant and surreal task. Yes, I say surreal because never in a million years would I have thought that I would end up spending an evening removing individual mouse turds from a TV set's RF coils with a pair of tweezers Still, it's all part of the hobby I suppose

Cheers
Andy
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