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Old 18th Sep 2019, 2:31 pm   #81
peter_scott
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Default Re: Yet Another Bush TV22

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I have my original TCC just the same as yours.

Awaiting stuffing.

Peter
Now stuffed.
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Old 18th Sep 2019, 3:59 pm   #82
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Default Re: Yet Another Bush TV22

There's an explanation how an efficiency diode line output stage works in the Philips section of the 1956/57 Radio and Television book. Pages 524 and 525.

DFWB.
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Old 18th Sep 2019, 4:40 pm   #83
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Default Re: Yet Another Bush TV22

I don't have that book but do have pages 277 Practical Television Jan 1958 and 325 etc Practical Television Feb 1958

Peter

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Old 18th Sep 2019, 5:13 pm   #84
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Default Re: Yet Another Bush TV22

Sorry, I got the link wrong. page 325 Practical Television Feb 1958.

and March 1958 page 358.

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Old 19th Sep 2019, 2:22 am   #85
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Default Re: Yet Another Bush TV22

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There's an explanation how an efficiency diode line output stage works in the Philips section of the 1956/57 Radio and Television book. Pages 524 and 525.

DFWB.
I never found a satisfactory description of how energy efficiency scanning worked, except for some brilliant research papers written by Otto Schade at RCA labs in the 1940's. It was Blumlein who patented the initial idea though.

Specifically, how the modern (valve) form of the line output stage evolved from earlier circuits. To explain it I created my own article which shows in progressive steps how the configuration came about and how to understand why it ended up this way, because it is not obvious from the existing format of the circuitry, where you see a situation where the energy recovery diode is tapped into part of a winding which appears as an autotransformer. To get to this requires a number of steps with equivalent circuits, see figures 7, 8, 9 & 9B and the associated text:

http://worldphaco.com/uploads/TELEVI...R_DIODE_OR.pdf

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Old 19th Sep 2019, 9:42 am   #86
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Default Re: Yet Another Bush TV22

It has to borne in mind that it is the second cycle of the flyback oscillation that has to be suppressed, damp or suppress the first cycle and the retrace energy will be lost.

DFWB.
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Old 19th Sep 2019, 12:48 pm   #87
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It has to borne in mind that it is the second cycle of the flyback oscillation that has to be suppressed, damp or suppress the first cycle and the retrace energy will be lost.

DFWB.
A bit of a simplification, its more about 1/4 and half cycles:

The H output stage epitomizes the two key aspects of everything we love about electronics, electric and magnetic fields and the energy exchange between those in resonant circuits.

At the end of the scan, on the right hand side of the raster, there is maximum magnetic field energy stored in the yoke and line output transformer. The device sustaining that current (the H output valve or the transistor) is driven into abrupt cut-off. The is leaves a resonant circuit of the inductance of the yoke, the H output transformer, their winding self capacitances and any tuning capacitance (often added in transistor circuits) to form a resonant circuit at around 60 to 80 kHz.

As the magnetic field energy collapses it is transferred to the electric field energy of the capacitance as it charges up in a sinusoidal manner. One quarter of a cycle into this oscillation, all of the magnetic field energy of the total inductance is transferred to the electric field energy of the capacitance. At this moment the flyback voltage pulse has peaked, and is rectified to develop the EHT. The voltage on the collector of the output transistor (or the plate of the output valve ) has peaked and there is no magnetic field energy at that moment, because, the yoke current is zero (of course it should be, as its half way into the flyback, the beam is obviously in the screen center line).

Then, on the next quarter cycle the voltage starts to drop, energy is returned from the electric field of the capacitance back to the magnetic field of the transformer and yoke. When the voltage hits zero, the energy now is all transferred back to the magnetic field of the yoke & output transformer. This is the start of a new scanning line, on the left side of the raster.

Of course, these oscillations would continue, and the plate or collector voltage then swing negative (after all the output device is still switched off) However, this is where the damper(efficiency) diode comes into conduction. This immediately damps the oscillations and causes the stored magnetic energy to 1) be returned to the power supply and 2) result in a near linear decay in yoke current to scan the left side of the raster. As the damped current decays away toward the center of the raster, the output device is turned on again.

So the flyback voltage spike you see represents a 1/2 cycle of the oscillation in the range of 60 to 80 kHz.

It was this cycle that inspired Blumlein to realize that H deflection circuits really only needed to be energy control and management circuits. If the bulk of the energy used to scan the beam to the right side of the raster could be recovered to scan the left side, all that would be required would be enough injection of energy to overcome losses. This was quite unlike earlier designs where the oscillations at flyback were merely damped away with resistors and the opportunity to recover a high peak voltage from a high Q resonant circuit, with an overwind on the transformer was lost.

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Old 19th Sep 2019, 1:21 pm   #88
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Default Re: Yet Another Bush TV22

Looking at my line scan it is compressed in the region that I assume is that corresponding to the transition from scan current taken from the boost capacitor to that from output valve. The nominal value of the boost cap is 2uF so I thought I would experiment with its value to see if I could alter my compressed region. I tried increasing to 3uF and also decreasing to 1uF but was very surprised at how little effect there was on the line scan.

Peter
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Old 19th Sep 2019, 3:34 pm   #89
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Default Re: Yet Another Bush TV22

Even if I ignore the linearity I have still a long way to go with picture centring.
This is with my best ion trap magnet and twisting the focus magnet assembly to its optimum. I've also tried general degaussing to all sides of the set.

Peter
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Old 19th Sep 2019, 5:27 pm   #90
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Default Re: Yet Another Bush TV22

Confessions: My C34 was leaky and running a small amount of dc through the scan coils and the line linearity adjusting screw had parted company with the slug. (The ghost vertical in the top right corner diagonals is just a reflection of something in the room.)

Peter
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Old 19th Sep 2019, 5:47 pm   #91
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Default Re: Yet Another Bush TV22

Excellent picture Peter!

Jac
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Old 19th Sep 2019, 5:57 pm   #92
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Default Re: Yet Another Bush TV22

Jac, you're a bad boy. Giving me hours of work and quite a few forum members spending time thinking about too.

The set would still have been gathering dust in the corner of the room if it hadn't been for you and I could have had my feet up watching a nice modern flat screen TV instead.

Peter
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Old 19th Sep 2019, 7:19 pm   #93
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Absolutely Peter!

Otherwise the set would be destined to eventually end up here:
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p.s. Sorry David - couldn't resist using your avatar...
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Old 19th Sep 2019, 7:49 pm   #94
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Default Re: Yet Another Bush TV22

That's a very good test card now peter , pleased to see that you got there in the end.

Robin
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Old 19th Sep 2019, 8:16 pm   #95
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Default Re: Yet Another Bush TV22

Thanks Robin and to everyone else who helped me on the way.

Peter
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Old 19th Sep 2019, 10:20 pm   #96
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Default Re: Yet Another Bush TV22

That does look good! Puts mine to shame, I think it’s time mine revisited the bench

Regards,
Lloyd
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Old 19th Sep 2019, 11:28 pm   #97
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Default Re: Yet Another Bush TV22

Lloyd, your ion trap comments were a big factor in the final result and without them I'd still be under the impression that as long as the magnet bends the beam that's all you need. I now know better and much appreciate your experience. I hope you will resurrect your TV22 and better my results.

Many thanks,

Peter
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