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Old 8th Mar 2015, 6:14 pm   #21
G3JZF_John
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Default Re: Baird P.2214

Hi DFDB

Thanks for the interest.
The date on the main smoothing electrolytic is Feb 55 - and it tests out OK. The valves are P series. ECL80s, EF80s etc. I think the tuner is a 5 channel Cyldon, but not sure all the coils are there.
I have replaced a number of capacitors and I will run it up on the Variac during the week to see what happens .

John
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Old 13th Mar 2015, 5:57 pm   #22
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Default Re: Baird P.2214

Hi Guys
I am now working on the set but really need the circuit. The one I have has a 12 position tuner with only some of the coils fitted. The timebase does have 2ECL80s and an ECC82 as well as the PL81 and PY81.
DFWB- Can you let me have the details of the book with the circuits, I can then hopefully get it from Birmingham Reference Library and copy all of the information on the variants and identify the one I have.
Many Thanks
John
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Old 13th Mar 2015, 10:27 pm   #23
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Default Re: Baird P.2214

Hi John,
Information for the Baird P2114 series can be found in the 1955/56 Molloy and Poole Radio and Television servicing book. The receivers described in this book are most likely to be similar to your model P2214.
The P2114 employs an ECC82 as the line oscillator valve (V11). An additional valve (V401) in the fringe area models is an ECL80 and functions as the line flywheel discriminator. The voltage present at the anode of the pentode section controls the line oscillator in terms of frequency and phase.
Most sets have a 13 channel Clydon tuner. However, some models were supplied fitted with a single band a 5 channel unit.
The Baird TV sets described in the 1956/57 R & T book are totally different being in fact rebadged Ambassador models.

DFWB.
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Old 26th Mar 2015, 4:55 pm   #24
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Default Re: Baird P.2214

Thanks to all for their help so far.

I have managed to get hold of the Molloy & Poole book vol 4.
I have nearly got the RF chassis working but really need a sig gen.
My Marconi TF888 is not working so I have ordered a set of valves.

Meanwhile I have stripped the cabinet and refinished it with stain and Dutch Oil. It has come up reasonably well. Not showroom condition, but OK for now.

One thing - Are the sound and vision IF frequencies in the 34 38 Mhz region ?


Many thanks

John
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Old 26th Mar 2015, 5:53 pm   #25
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Default Re: Baird P.2214

The TF888 is much more likely to need attention to its rectifiers or capacitors more than the valves. It is possible though obviously and DL92`s are cheap enough.
You will need an oscilloscope to make sure it is doing what its supposed to.
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Old 26th Mar 2015, 6:54 pm   #26
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Default Re: Baird P.2214

Stephen

Well, I have checked the rectifiers and capacitors in the power supply and apart from the HT being a few volts down it seems OK. I swapped a couple of the DL92s over and the output is nil- It was giving some output before.

I will await the new valves and take it from there.
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Old 11th May 2015, 4:03 pm   #27
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Default Re: Baird P.2214

Good Progress on the Baird

I am pleased to say that I am progressing with the Baird P 2214.
After recapping the timebase section, cleaning the contacts in the turret tuner and replacing the contrast (shade) control I was rewarded with a good bright and contrasty picture. The line had very poor locking and I will need to sort that out.
Unfortunately, after the set had been on for about 5 minutes there was an ominous fizzing from the EHT and I switched off to avoid the LOPT failing.
I am now asking if there are any magic dips sprays etc out there which may save the transformer.

I was pleased to meet many of you at Mike's place the other day and we all owe him a great deal of thanks for putting on the event.

John
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Old 13th May 2015, 6:28 pm   #28
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Default Re: Baird P.2214

Getting There !!

The LOPT problem was easily solved - I just blew hard on it -perhaps it helps to be a tuba player! -and must have cleared whatever was casing the arcing.

The remaining problem is that I have had to turn the contrast up a lot to get the picture to lock.

I now need to sort out the sync separator and timebase circuits.

John
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Old 13th May 2015, 8:55 pm   #29
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Default Re: Baird P.2214

Here are the latest screenshots.

John
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Old 13th May 2015, 10:03 pm   #30
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Default Re: Baird P.2214

Hi John,
The picture looks to have excellent contrast. I notice that there is a slight fold over at the extreme left side of the picture. A problem most likely to be in the flywheel line sync discriminator circuit.
The operation of the line sync discriminator is described in the 1955/56 R&T servicing book. An extra valve V401 which is an ECL80 triode-pentode performs the line sync discriminator function. The triode section inverts the negative going sync pulses from the sync separator. The sharpened up +ve syncs are supplied to the control grid of the pentode section. The reference pulses are developed across the cathode resistor of the PL81 line output valve. The pulses are supplied to the anode and screen grid of V401. The resultant voltage present at pin 6 is applied to the line multivibrator. An inductor, L401 is connected to the cathodes of the ECC82 line oscillator valve. To adjust this coil, first short it out, then adjust the line hold control to achieve a stationary picture. Remove the short circuit and then adjust L401 for a stationary picture. I'd reckon this coil also effects the phasing of the line sync.

DFWB.

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Old 14th May 2015, 11:25 am   #31
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Default Re: Baird P.2214

Hi DFWB
Yes the picture has very good brightness and contrast - the tube is clearly a good one.

My set does not have the flywheel sync. circuit and lacks the extra valve. I am sure the problem is in the sync separator area because I to wind up the contrast almost to overload to get the timebases to lock. I'll have a look at the waveforms with my scope and check over the components to try to sort it out. I also need to tweek the tuner so that the fine adjustment is not at its limit.

Do you have the circuit for the non fringe version and any other service data that may be useful?

I will keep posting the progress.

John



bas
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Old 14th May 2015, 3:34 pm   #32
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Default Re: Baird P.2214

Hi John,
The circuits are from the 1953/54 R&T servicing book. Some early sets employed a blocking oscillator in the line timebase using the triode section of an ECL80. The pentode functions as the frame output valve. The circuit shown here uses the triode section of an ECL80 and the PL81 line output valve to form a multivibrator circuit.
Later sets employed an ECC82 double triode in a cathode coupled multivibrator circuit.

DFWB.
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Old 14th May 2015, 4:08 pm   #33
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Default Re: Baird P.2214

Hi again DFWB

Many thanks for the circuits. The second one is almost certainly the right one.
I ran the set for about 2 hours this morning without distress but it is not right yet. I changed the sync separator/frame output valve for a NOS which did improve things. See attached screen shots. I still have to turn up the contrast to get a lock and loose the detail in the blacks. I need to check the 500mF cathode decoupling capacitor and I suspect that the blanking feed to the tube grid is not right.
Now that I have the correct circuit and some waveforms to work on I will press onward.

Thanks again,

John
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Old 17th May 2015, 4:02 pm   #34
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Default Re: Baird P.2214

Grid Cathode Conductivity

Just when I thought I had sorted out all the problems and could have posted some nice pix, I have come across this problem:

I could not get rid of the flyback lines in the frame blanking period and set about sorting out the problem.
I found that the blanking pulse to the grid was shorting out. After a bit of head scratching, I measured the grid/cathode resistance and discovered it was not infinite. It measured 3.1 megohm on my best DMM. This was measured cold with nothing connected externally. The only possible thing is that there may be some crud in the valvebase - unlikely.
Before thinking in terms of a work-around and reducing the impedance of the blanking circuit, I am seeking the opinions of those 'skilled in the art' who may be able to shed some light on the issue.

Many Thanks

John
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Old 17th May 2015, 6:34 pm   #35
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Default Re: Baird P.2214

The frame blanking pulse is derived from the timebase multivibrator. Reference to the second attachment on post #32. The pulse present across C75 is supplied to the grid of the CRT via a 47Kohm resistor and a 0.1mfd capacitor. A 0.005mfd capacitor is connected between the junction of the these two components. It could be leaky. The slider of the brightness control connects to the grid of the CRT via a 150Kohm resistor.

DFWB.
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Old 19th May 2015, 9:08 pm   #36
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Default Re: Baird P.2214

DFWB

Thanks for the info.
I still think there is a grid-cathode leakage on the tube and decided to disconnect the blanking feed to the grid and tie it down to ground with a 0.1 mfd capacitor. That has cleared things up a lot and get good picture without the blanking.
It looks as if I need to sort out video stage to get a better grey scale and I may be able to clear up the overshoot.
Sorry about the camera shutter problem. I need to pop it on a tripod,stop down and use a longer exposure.

Cheers

John
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Old 24th May 2015, 4:13 pm   #37
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Default Re: Baird P.2214

Nearly There !!!

I have been working on the set and really believe that I have nailed most of the niggles.
I still think I can improve things by tweaking the bias on the video amplifier. That way I think I can bring up the video more out of the black and at the same time increase the sync to the separator. The frame locking is rather critical at the moment.- Perhaps a new valve will help.

Anyway, here is the latest picture.

John
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