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Old 4th Oct 2019, 11:00 pm   #121
FERNSEH
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Default Re: Bush TV22 with TC184 B3 converter.

Hi Peter,
Does the TV32 have an interlace control?

Getting back to the TV22. I've measured the ripple on the HT line supplying the sync separator and frame timebase. It is 20V P - P. Possibly that's why the interlace is bad. Scope set to 1volt/division and using a X10 probe.

DFWB.
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Old 4th Oct 2019, 11:30 pm   #122
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Default Re: Bush TV22 with TC184 B3 converter.

Found the TV32 interlace control. It's located to the right of the switched width control. Adjust in conjunction with the frame hold control. Adjust the frame hold to the point where the picture just start roll, then turn back to lock the picture. Adjust the interlace control for best results, somewhere between picture jitter and the picture starting to roll.
Good interlace is possible with this set.

DFWB.
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Old 4th Oct 2019, 11:30 pm   #123
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Default Re: Bush TV22 with TC184 B3 converter.

One interesting thing about getting the V sync pulse filter right in the set, if the output from the filter is disconnected from the V osc, it changes its properties. So ideally to do it, the V osc is stopped and the scope is put on the valve's grid, so the final sync pulse you see there also includes the effects of the blocking osc transformer and is the actual pulse that triggers the V osc.
Yet although RCA recommended stopping the V osc, they did not explain how it should be done.
Looking at the TV22 circuit as one example in post 69, I think the best way to do it would be with a 9V battery, positive to ground and negative connected to C4. This will prevent C4 charging up and it will hold the grid negative keeping the valve cut off. Then the scope can be placed on the valve grid to look at the sync, Then the resistors in the filter adjusted to get the correct result where the H serrations are just eliminated.

20V ripple seems very extreme for the supply of a V osc.
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Old 5th Oct 2019, 12:18 am   #124
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by peter_scott View Post
Do you find your interlace control does much?
Hi Peter. It does not seem to do much on my T36. Actually I really hate the set as it is such a pig to work on. It is having the later RF deck from the TV43 that makes it difficult. I only have a T36 as it is the same as the first set in the family.
Anyway, I'm keen to see how everyone gets on with the TV32 circuit as it might inspire me to take my set apart again and sort it out.

Btw, the TV show was the Adventure Game, from 1983.

Cheers
Andy
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Old 5th Oct 2019, 9:08 am   #125
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by Argus25 View Post
if the output from the filter is disconnected from the V osc, it changes its properties. So ideally to do it, the V osc is stopped and the scope is put on the valve's grid, so the final sync pulse you see there also includes the effects of the blocking osc transformer and is the actual pulse that triggers the V osc.

20V ripple seems very extreme for the supply of a V osc.
Hi Hugo,

The sync in these sets is inserted at the anode not the grid.

In the TV32 that I'm finding sensitive to ripple I have 600mV of ripple on the HT. I tried decoupling the anode feed to the sync separator and gave it a clean supply but it would appear that it is the oscillator that is problematic. Placing a modern 250uF electrolytic on the rail certainly helped.

Peter
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Old 5th Oct 2019, 9:12 am   #126
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by beery View Post
I'm keen to see how everyone gets on with the TV32 circuit as it might inspire me to take my set apart again and sort it out.
..cheers
Andy
Hi Andy,

The TV32 is certainly not as easy to work on as the 22 because you are stuck with main chassis in the cabinet. It sounds as if David's one syncs a lot better than mine.

Peter
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Old 5th Oct 2019, 10:26 am   #127
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by peter_scott View Post
The sync in these sets is inserted at the anode not the grid.

In the TV32 that I'm finding sensitive to ripple I have 600mV of ripple on the HT. I tried decoupling the anode feed to the sync separator and gave it a clean supply but it would appear that it is the oscillator that is problematic. Placing a modern 250uF electrolytic on the rail certainly helped.
Peter,

You misunderstood what I was getting at.

The output of the vertical sync/integrator is physically connected to the anode, but it acts by producing a positive pulse at the grid. So the loading on the filter RC network is affected by the impedance at the anode and what you get at the grid also depends on the frequency response properties of the transformer.

So, ideally, to get the integrator correct, it should not be disconnected from the anode circuit and ideally the V sync pulse that is being monitored on the scope is monitored on the grid connection after it has been processed through the transformer as it is in use/operation.

Therefore, to get the best result, modifying the integrator (100k replaced with one gang of a 50k pot and the diode replaced with the other gang of the 50k pot and adjusting its so the sync pulse seen at the GRID is just free of H serrations) is done with the same conditions loading the filter that are happening it use.

To get the above, it's better that the valve is cut off and the oscillations have to be stopped and the scope placed on the grid connection.

In use just prior to the initiation of vertical fly back (the vert osc valve triggered into conduction) the Grid is negative, the sync pulse comes along at the grid at a + going pulse and triggers the valve into conduction. This is why I suggested the battery to disable the oscillations and put the DC grid voltage into the negative region to check the form of the sync pulse at the actual grid with the scope.
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Old 5th Oct 2019, 1:25 pm   #128
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Default Re: Bush TV22 with TC184 B3 converter.

Argus25 wrote: "The output of the vertical sync/integrator is physically connected to the anode, but it acts by producing a positive pulse at the grid. So the loading on the filter RC network is affected by the impedance at the anode and what you get at the grid also depends on the frequency response properties of the transformer."

So ideally a buffer/inverter stage should be inserted between the frame sync integrators and the oscillator. A correctly shaped positive sync pulse will be supplied to the valve grid instead having been distorted by the oscillator transformer.
When transistors came along all these circuit functions could be cheaply implemented but with valves it's not only the cost of the valve that has to be considered but also the assembly time.

DFWB.
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Old 5th Oct 2019, 2:10 pm   #129
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Default Re: Bush TV22 with TC184 B3 converter.

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Originally Posted by FERNSEH View Post
So ideally a buffer/inverter stage should be inserted between the frame sync integrators and the oscillator. A correctly shaped positive sync pulse will be supplied to the valve grid instead having been distorted by the oscillator transformer.
The transformer conveniently inverts the signal, there is no need for an extra active stage to do it.

The point is though, you are interested in the quality of the sync pulse as it appears at the grid, that it has been correctly filtered. If under filtered there are H serrations that cause poor interlace, if over filtered the amplitude is lower and the rising edge slower and more possibility for external interference H signals or power supply ripple to affect the interlace.

Some filtering will be achieved by the transformer (due to its limited high frequency response) most of the filtering by the integrator RC components.

However the RC filter-integrator loads into the anode circuit and is affected by the impedance there. So, when it comes to adjusting the filter (resistor or capacitor values) it is better not to alter the circuit by disconnecting the filter/ integrator output from the anode circuit, it is better to simply monitor the form of the vertical sync pulse on the valve grid, with the V osc disabled. This way the V sync waveform you see will be what is actually there in practice later when the oscillator is running/ enabled.

In summary, use the battery to disable the V osc (CRT brightness on zero), have the dual gang 50k pot or similar fitted in place of the 100k resistor & the diode. Adjust it so the sync pulse waveform at the grid on the scope is just free from H serrations and perhaps a tad higher resistance at that point, fit fixed resistors . And if still troubles, then make sure the HT supply to the V osc is free from interference by H pulses or 50Hz ripple and after that you will have the best interlace you can possibly get.
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Old 5th Oct 2019, 3:30 pm   #130
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Default Re: Bush TV22 with TC184 B3 converter.

Replaced the 2M frame linearity pot and that has reduced the random noise. Also replaced the boost line reservoir cap and the screen decouplers for sync sep. and frame output and its cathode bypass and the rather interesting cap coupling the HT to sync sep. cathode. I think I've replaced all the sync and frame circuit caps with the exception of the two 200pF mica caps in the feedback.

I think the linearity pot was the largest noise contributor although it still twitches a bit but Hugo's RCA integrator definitely helps.

https://youtu.be/t7Poh6CB0l8

Sitting back from the screen it's not perfect but much better than it was.

Peter
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Last edited by peter_scott; 5th Oct 2019 at 3:39 pm.
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Old 5th Oct 2019, 3:33 pm   #131
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Default Re: Bush TV22 with TC184 B3 converter.

A number of 405 line sets did have a frame sync pulse inverter. I think my Pye V600A has one which comes as a surprise because most of the chassis design was done on the cheap. Interlace on that set is excellent which is just as well as the V600A has a 23" CRT.
The set I'm looking forward to restoring is the huge Kolster-Brandes "Regina". This late fifties set has a 24" CRT. What's 405 going to look like on that set?

DFWB.
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Old 5th Oct 2019, 10:47 pm   #132
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Default Re: Bush TV22 with TC184 B3 converter.

The attachment shows the interlace filter employed in the Pye V600A.
As Hugo states the negative going sync pulse can be supplied to the anode of the blocking oscillator valve and there is not requirement for a frame sync pulse inverter.

DFWB.
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Old 6th Oct 2019, 1:16 am   #133
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Default Re: Bush TV22 with TC184 B3 converter.

One other thing, obviously , just as applies to the V osc stage, the power supply to the video stages and sync separator must be relatively free of hum modulation, otherwise the signal from the sync separator could have hum (amplitude) modulation on it, which will still be there after the vertical integrator and could possibly upset the interlace if the form/shape of the V sync pulse is getting altered by hum voltages. Probably all of these old sets are better off with new electrolytics in the power supply sections.
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Old 6th Oct 2019, 8:47 am   #134
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Default Re: Bush TV22 with TC184 B3 converter.

Quote:
Originally Posted by FERNSEH View Post
The set I'm looking forward to restoring is the huge Kolster-Brandes "Regina". This late fifties set has a 24" CRT. What's 405 going to look like on that set?
DFWB.
As the Old Queen would have said. 'We are not amused'. J.
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Old 6th Oct 2019, 8:55 am   #135
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Default Re: Bush TV22 with TC184 B3 converter.

She would probably have liked test cards with lacy edges.

Peter
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Old 6th Oct 2019, 11:46 am   #136
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Default Re: Bush TV22 with TC184 B3 converter.

Power supply circuits employed the TV22 and the later TV22A and TV24C.
For HT smoothing the early production sets have capacitors and two chokes.
Later production models TV22A and the two band TV24C have resistance and capacitor smoothing. In both versions the 0.75mfd ripple filter capacitor is used

DFWB.
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Old 7th Oct 2019, 11:59 am   #137
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Default Re: Bush TV22 with TC184 B3 converter.

I can't say I'm all that happy about abandoning the original circuit but I must admit that with a 3 stage RC filter 3 x 10k/0.0068uF the trigger pulse looks much cleaner and triggering more stable and interlaced.

https://youtu.be/JzJ4Lik8R90

Excuse the poor resolution and aliasing in the Youtube:

https://youtu.be/Lgz08qIv20c

Peter

Last edited by peter_scott; 7th Oct 2019 at 12:28 pm.
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Old 7th Oct 2019, 2:44 pm   #138
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Default Re: Bush TV22 with TC184 B3 converter.

I know what you are getting at and it is a difficult notion to modify a circuit to be far away from what it was as new because part of the charm of these old sets is their circuit quirks.
For the TV22 I would go for a compromise, just leave it there as it is but tack a resistor across the existing 100k and tack a resistor across the diode(it may not be necessary to disconnect the diode from its solder tags) to give the best sync pulse form at the grid and best interlace you can get with the existing capacitors and then what amounts to a 2 stage filter, then a purist could simply remove them one day to restore the original circuit.
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Old 7th Oct 2019, 3:03 pm   #139
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Default Re: Bush TV22 with TC184 B3 converter.

Here's a slightly higher res video:
https://youtu.be/Z4qF1uisE04

It looks like in YouTube you need to hit the settings and select 1080 otherwise it defaults to 480.

Peter

Last edited by peter_scott; 7th Oct 2019 at 3:14 pm.
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Old 7th Oct 2019, 3:19 pm   #140
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Default Re: Bush TV22 with TC184 B3 converter.

Argus25 wrote: "I know what you are getting at and it is a difficult notion to modify a circuit to be far away from what it was as new because part of the charm of these old sets is their circuit quirks.
For the TV22 I would go for a compromise, just leave it there as it is but tack a resistor across the existing 100k and tack a resistor across the diode(it may not be necessary to disconnect the diode from its solder tags) to give the best sync pulse form at the grid and best interlace you can get with the existing capacitors and then what amounts to a 2 stage filter, then a purist could simply remove them one day to restore the original circuit."


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?

DFWB.
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