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Old 7th Oct 2019, 3:47 pm   #141
Argus25
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by FERNSEH View Post
The TV22 isn't a rare set so why not go ahead and improve it to a certain extent. Anyway, was that 100K resistor a mistake made not by the designer but perhaps someone in the components procurement department?
I guess it could just have been an administrative blunder that the resistor was off by a factor of 10, but I don't think likely, because the diode in that part of the circuit has no useful application and it is also wired in a manner, with no DC reference, that the leakage properties of the actual diode and microscopic capacitor leakage would throw in a lot of variability between sets. I just think for this small part of the circuit the designer dropped the ball and didn't understand the requirements of the vertical integrator for a good interlace.

Mind you as I mentioned, it did not seem to be an area well covered in English TV sets of the era and the only documentation I have seen that covered the integrator design properly was from RCA. For example in their design paradigm there is no such thing as an "interlace diode". I think it is just an area that slipped by, that is until the CRTs got bigger and it became more obvious when the interlace was poor, until the 1960's when practically all sets had a proper integrator network.

The TV 22 is rare from my perspective, very few of them made it to Australia.

I still try to keep the circuits as close to standard as possible in my restorations, but don't mind improving them with extra parts tacked in. In my HMV904 I tacked in a few parts to extinguish the CRT beam at power down, to help protect the CRT phosphor for example and a circuit change to protect the CRT when it's switched to radio mode as one example.
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Old 7th Oct 2019, 4:34 pm   #142
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Default Re: Bush TV22 with TC184 B3 converter.

Just maybe it may have performed slightly better with a live transmission? We will never know. John.
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Old 7th Oct 2019, 9:19 pm   #143
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Default Re: Bush TV22 with TC184 B3 converter.

Extract from the RCA CTC11 circuit diagram.
This receiver has the two stage frame sync integrator.

DFWB.
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Old 7th Oct 2019, 10:22 pm   #144
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Default Re: Bush TV22 with TC184 B3 converter.

Just a quick question; if the TV22 did have a significant design flaw in this part of the circuit, how come it generally worked so well and this wasn't picked up in subsequent updates?

I have a mix of four working TV22 and TV24 sets, both MkI and MkII, and although their basic design has other shortcomings, I haven't noticed interlace problems on any of them.

Ian
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Old 7th Oct 2019, 10:56 pm   #145
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Default Re: Bush TV22 with TC184 B3 converter.

I think that could be explained by some factors, those described in the post #141 first paragraph about "variability between sets" and also as noted on a CRT of the size used in the TV 22, without a very well focussed beam and a crisp looking test pattern image it can be difficult to see.

Also, I had not detected it myself in my own TV22 until (I think it was Peter who pointed it out on another thread where I had posted a screen image or it may have been my 904) noted that the interlace was defective and most of the time otherwise I would spot fairly quickly any defects in the image. But when it was pointed out I could see it.So after that I investigated the integrators.

See if you can get a good test pattern photo from your TV 22, & post it for examination.

Last edited by Argus25; 7th Oct 2019 at 11:06 pm.
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Old 7th Oct 2019, 11:05 pm   #146
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Ian - G4JQT View Post
I haven't noticed interlace problems on any of them.
Hi Ian,

If you look at post #78 in page 4 of this thread I compare a set with good interlace in the first frame of the triptic with my TV22 in the second frame using the standard circuit. The third frame shows the effect of changing the 100k to 10k followed by a couple of details from the two TV22 shots. Keith also reported poor interlace on his TV22.

Peter
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Old 7th Oct 2019, 11:24 pm   #147
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Default Re: Bush TV22 with TC184 B3 converter.

Also there is this: In cases of under integration it's the H serrations that cause poor interlace, but in the TV22 a case of over integration. I think what happens here is it simply renders the V osc more susceptible to interfering H pulses from elsewhere and or 50Hz ripple on the supply rails that make the interlace appear to come and go at times. So maybe, when these sets were brand new, the over integrated vertical sync was not as much of an issue as we see when the 50Hz ripple and H pulses get superimposed on the HT lines increase.
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Old 8th Oct 2019, 12:49 am   #148
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Default Re: Bush TV22 with TC184 B3 converter.

At the time the TV22 was designed and made the TV transmitter sync pulses were locked to the 50 cycles/second mains supply. The very slight variations in frequency didn't matter as long as the correct number of lines was transmitted. This practise of gen lock was stopped about 1964.
I remember about that time many viewers complained that the picture suddenly took on a "breathing" effect. The problem was caused by inefficient HT smoothing.

DFWB.
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Old 8th Oct 2019, 8:02 am   #149
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Default Re: Bush TV22 with TC184 B3 converter.

That makes a lot of sense because the ability of interfering hum in the V sync pulse to interfere with the v oscillator would be a lot less noticeable if the field rate of the video signal was essentially phased or frequency locked to the mains frequency.

It also would have meant that the manufacturers of say a TV22 could have gotten away with lower uF value filter caps, and they already had over double the requirement with a 1/2 wave rectifier system anyway, vs full wave in many American sets and the Americans had an additional advantage of 60 Hz too further improving their situation with filter cap values.
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Old 8th Oct 2019, 10:42 am   #150
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Default Re: Bush TV22 with TC184 B3 converter.

In fact a special version of the TV22 was made for Northern Ireland because the mains supply there was not connected to the national grid of the mainland.
The TV22U as it was designated had extra HT supply smoothing so that the receiver would operate satisfactorily on the unsynchronised mains supply.
It should possible to find the service manual supplement for the model TV22U.

DFWB.
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Old 8th Oct 2019, 11:35 am   #151
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Default Re: Bush TV22 with TC184 B3 converter.

Thanks Peter and Argus. I've only had access via a phone recently so not been as thorough at reading through the thread as usual.

Here are my TV22 images. Classic poor interlace or as expected...?

All images the same, just trying to avoid some of the digital camera artefacts.

Ian
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Old 8th Oct 2019, 1:06 pm   #152
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Default Re: Bush TV22 with TC184 B3 converter.

Hi Ian,

Your test card fills the full frame the same mine but if you count the number of lines over the grating I think you will see 11 lines in the crop from your photo. (left hand image) Now look at my modified TV22 (image on the right) and you can count twice the number of lines. You might question why the intermediate lines appear lower in brightness but this is simply because the camera is seeing the second scan after the phosphor has decayed slightly. If the exposure was longer then many scans would average out the brightness.

It's possibly easier to see in the second comparison with your set on the left and a good 405 line set on the right.

Peter
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Old 8th Oct 2019, 9:58 pm   #153
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Default Re: Bush TV22 with TC184 B3 converter.

The Bush TV12 employed a similar two deck construction technique as the TV22. The frame timebase consisted of an EF50 pentode operating as a Miller oscillator and an EL42 for the output. The frame sync circuit is similar to the TV22 inasmuch it has a WX6 Westector interlace diode. Shorter integrator time constants so perhaps the interlace is better than the TV22?

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Old 8th Oct 2019, 11:46 pm   #154
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Default Re: Bush TV22 with TC184 B3 converter.

The circuits with the Westector diode in the TV22 are interesting. If you assume the diode has around 100k leakage or less (would be interesting to measure it) the average diode anode voltage would simply climb to the plate circuit voltage of the sync sep stage. Then when the leading edge of a negative going pulse appeared the diode would assume a low resistance and when the plate voltage went high again the diode would stop conducting and go back into leakage mode acting like a high value resistor.

So it appears as if the designers wanted a filter with a fast attack and a slow decay. Which to some extent makes sense and another not.

It is the leading edge of the vertical sync that is important with vertical lock and interlace timing. Once the vert osc is triggered into flyback and the valve is conducting for a 1/2 cycle of oscillations of the blocking osc transformer, after that is initiated, it is academic what the rest of the sync pulse is like (provided it doesn't extend pass the end of V flyback). Even if it did extend past the end of V flyback, the voltage during the start of scan at the grid is very negative keeping the valve heavily cut off and any sync pulse voltage still trailing into that time would get ignored, at least for a blocking oscillator.

So the diode appears to confer no advantage over a resistor of some value. Yet at the time it must have been a lot more expensive, so they must have observed some advantage of it with interlace to have given it that name "interlace diode". Though it might have been a kludge that appeared to mask over other issues such as the V osc being susceptible to mains hum or H pulses. As noted there is no such thing as an interlace diode in any American set or their literature that I have ever seen at least. They were not shy to use diodes in sync systems though, say in the H flywheel sync circuits.

So on the one hand the the TV22 designers were interested in a well filtered pulse with a fast attack or fast rise, but on the other hand they totally over did the integration with that large value of 100k.

Maybe as suggested it was a simple blunder and it was meant to be 10k all along.

Last edited by Argus25; 8th Oct 2019 at 11:51 pm.
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Old 9th Oct 2019, 7:28 am   #155
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Default Re: Bush TV22 with TC184 B3 converter.

....I have been thinking about this whole business with the interlace diode in UK TV sets. It makes a lot more sense if it was intended for a system free from equalisation pulses.

In effect what was done with the diode was to create a charge pump with a fast attack and a slow decay. This is a good idea to help eliminate H pulses, unless there are equalisation pulses present in the composite sync which upset the apple cart with the charge pump idea.

If there are equalisation pulses in the composite sync train, it is much better with no diode and just a resistor instead. Perhaps this is why the diode is not present in the American TV set designs where there were always equalisation pulses.
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Old 9th Oct 2019, 9:41 am   #156
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Default Re: Bush TV22 with TC184 B3 converter.

TV22U This is a version of the TV22 designed especially for used on unsynchronized mains.The principal difference lies in more elaborate HT smoothing. C67 is replaced by a 60uf electrolytic with a 250uf in parallel with it while C66 remains at 250uf, and C65 at 60uf. These four capacitors comprise two 60+250uf units. Also instead of a separate HT feed line from the junction L30, C67. both of the lines we show are joined together and come from the junction L30,C67. R66 and C64 are omitted.

From Trader sheet 1091/38. [They probably interlaced Ok when locked to the mains supply. I think it was unlocked in 1964 and can remember having to change large numbers of smoothing blocks in the Regentone Ten4 series. I was 16!] John.
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Old 11th Oct 2019, 4:39 pm   #157
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Default Re: Bush TV22 with TC184 B3 converter.

NEWS FLASH! A Bush TV32 has come into the workshop with the report that the frame timebase has failed. Initial tests reveal that the blocking oscillator has an open circuit winding. The frame timebase circuit is very similar to the TV22. The exceptions are the omission of the interlace diode and the addition of a preset interlace control.
The oscillator transformer is of a different construction to the one in the TV22.

DFWB.
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Old 11th Oct 2019, 5:15 pm   #158
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Default Re: Bush TV22 with TC184 B3 converter.

Showing the suspect frame oscillator transformer.

DFWB.
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Old 11th Oct 2019, 5:41 pm   #159
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Default Re: Bush TV22 with TC184 B3 converter.

Hi David. Actually it is the same transformer as the TV 22, but it is wearing a tagboard hat as a disguise! When the one in my T36 failed, I was able to use a spare TV 22 one by fitting the transformer u clamp over the laminations and extending the leadout wires to reach the tagboard hat on the top.

Cheers
Andy

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Old 11th Oct 2019, 5:57 pm   #160
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Default Re: Bush TV22 with TC184 B3 converter.

Hi Andy,
That's what I'll have to do to get the set going again. This is the set that received it's replacement MW36-24 tube from the Sobell donor set. You'll recall that the Sobell had all sorts of awful things done to it.

DFWB.
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