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[Sticky] 1956 Pye 405 line NTSC CTV.  

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Till Eulenspiegel
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The 1000microfarad 12volt reversible electrolytic capacitor which is in series with the frame scanning coils was replaced today. Also the PL82 frame output has been substituted with the PL84.   The PL84 was introduced in 1956 the same year the Pye  405 line TV set was made.  Although PL84 is well known as a frame output valve in TV receivers having 110 degree CRTs I believe the valve was originally intended to be an audio output valve in TV receivers.

Also replaced are the DY86 EHT rectifier valves with the later DY802.

Focus control insulated shaft replaced with a longer one so now it is possible to adjust it with back cover in place.

Luminance delay line replaced with one from a GEC C2110.

The results of all these efforts.   No improvement in frame linearity but there is more spare picture height.

The EHT regulation is much better with the DY802 EHT rectifier valves but a beam current limiter would still be a desirable addition in the circuit.

Till Eulenspiegel.

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Topic starter Posted : 27/04/2019 10:32 pm
PYE625
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That frame linearity issue is a real mystery.... on the face of it, you would think an easy thing to correct.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 28/04/2019 10:06 am
Nuvistor
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This circuit was developed in the middle 60’s by Amperex to use its new series of valves for the line output stage.

The valves 6KG6 output, 6EC4 boost diode (damper) and 3BH2 high voltage rectifier using 9 pin glass bases. The circuit is interesting due to the use of a VDR to stabilise the stage and hence the EHT. A similar idea was used in UK BW sets from around 1963/64. 

The specified regulation of the EHT was 24KV at 0 beam current to 21.5KV at 0.85ma. Although Amperex state that this was adequate it appears much worse that the shunt regulation circuit designed to hold the high voltage steady from 0 to 1ma. The new circuit would I believe use less power and allow reductions in components and cost, I wonder how well it performed. 

The UK valve design circuits using a tripler never seemed to have the same stiff regulation as the shunt circuit.

Further reductions in cost the article states would be to use a voltage divider from the EHT instead of the focus rectifier circuit and with tight tolerances will require no horizontal shift control.

Ref Radio-Electronics Jan 1966.

17FE32FC CE59 4F9B 8982 9C707290902C

Frank

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Posted : 28/04/2019 2:26 pm
Nuvistor
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From WWJuly 1950.

E583AAE7 BF92 4D2E 9F36 637787A7E634

Frank

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Posted : 28/04/2019 5:14 pm
ntscuser
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Posted by: Nuvistor

From WWJuly 1950.

E583AAE7 BF92 4D2E 9F36 637787A7E634

That was a mechanical sequential colour system I believe similar to the one developed by CBS in New York. It was used to relay the 1953 coronation procession to the children's ward but probably had a more serious use as a teaching aid in live surgery.

Classic TV Theme Tunes

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Posted : 29/04/2019 2:47 am
Till Eulenspiegel
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Posted by Pye625 

That frame linearity issue is a real mystery.... on the face of it, you would think an easy thing to correct.

Hi Andrew,

the sawtooth waveform present at the grid of the frame output valve is perfectly linear. Without doubt the cause of the non-linearity is in the output transformer secondary circuits. Various frame output transformer have been tried.

Hi Frank,

those valves employed in the 1966 stabilised colour TV line output stage are in fact re-designated Philips sourced  types:

6KG6 = EL509. 6EC4 = EY500. 3BH2 = GY501.

https://www.radiomuseum.org/tubes/tube_3bh2.html

Till Eulenspiegel.

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Topic starter Posted : 29/04/2019 9:41 am
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Till Eulenspiegel
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Suggested circuit for a beam limiter. The values of the three resistors Rlim can be determined by experiment.  The voltage developed across the summing resistor can be used to control the vision AGC or alternatively a contrast control device in the luminance circuits.

Till Eulenspiegel.

PyeCTV Beam Current Limiter
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Topic starter Posted : 29/04/2019 10:21 am
Nuvistor
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Posted by: Till Eulenspiegel

Posted by Pye625 

That frame linearity issue is a real mystery.... on the face of it, you would think an easy thing to correct.

Hi Frank,

those valves employed in the 1966 stabilised colour TV line output stage are in fact re-designated Philips sourced  types:

6KG6 = EL509. 6EC4 = EY500. 3BH2 = GY501.

https://www.radiomuseum.org/tubes/tube_3bh2.html

Till Eulenspiegel.

That raises the question in my mind, did Amperex just import the valves rebadged from Philips or have them made in the USA with a licensing deal, if they hoped to sell lots they probably had or would have had a license.

Thanks for the information David, I didn’t look further than the article.

Frank

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Posted : 29/04/2019 5:23 pm
Till Eulenspiegel
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Hi Frank,

Seems that Amperex  was acquired by Philips in 1955.  Those CTV valves we discussed earlier in this topic  were imported from Holland. From Wikipedia:   https://en.wikipedia.org/wiki/Amperex_Electronic

Till Eulenspiegel.

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Topic starter Posted : 29/04/2019 7:20 pm
Till Eulenspiegel
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Over the past two days I've been trying various frame output transformers with the hope that a better one can be found. Even one from a Decca Battersea chassis. No success, so it'll have to be more modifications to the frame output circuit.

Till Eulenspiegel.

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Topic starter Posted : 01/05/2019 9:26 pm
Till Eulenspiegel
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Results from todays work done to the frame timebase.

The 0.1mf coupling capacitor between the oscillator and height control replaced by one of 0.5mfd.   Also, the linearity feedback capacitor returned to the original value of 0.1mfd and connected to direct to the anode of the PL82.  The two 18Kohm resistors fitted  across the primary of the output transformer now removed from the circuit.

The linearity is still not perfect but it's considerably better than it has been.

Till Eulenspiegel.

Pye 001 0214
PyeCTV0101
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Topic starter Posted : 02/05/2019 2:08 pm
The_Teleman, malcscott, Red_to_Black and 2 people liked
PYE625
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The linearity looks far better than anything before.... well done ?

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 02/05/2019 5:09 pm
Nuvistor
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Yes it does look much improved. ?

Frank

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Posted : 02/05/2019 6:03 pm
Till Eulenspiegel
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Good evening Gentlemen,

Thanks for your comments. I reckon the linearity can be further improved by changing the 1000microfarad series capacitor between the transformer secondary and scan coils with one of 2000mfd.  The purpose of the capacitor is to allow for the injection of a controlled DC in the scanning coils for vertical picture shift.

Till Eulenspiegel.

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Topic starter Posted : 02/05/2019 8:59 pm
Till Eulenspiegel
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The attachment shows just how bad the frame linearity was.

Till Eulenspiegel.

PyeCTV
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Topic starter Posted : 04/05/2019 3:21 pm
Till Eulenspiegel
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The redrawn circuit of the frame output stage.  The 1000 microfarad reversible electrolytic capacitor has been replaced with a series connected 2200 + 2200 microfarad capacitor. This is not a nice solution and in due course it will be replaced with the correct type of capacitor having the correct properties.  Picture shift choke apart the circuit isn't all that different from the frame timebases in colour TV sets made eleven years later.

The PL84 will replace the PL82.

Till Eulenspiegel.

PyeCTVframeTB

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Topic starter Posted : 09/05/2019 8:26 pm
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PYE625
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Hi, I'm curious as to why the 10uf capacitor to the screen has it's negative connected to the cathode, not ground.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 09/05/2019 8:45 pm
Till Eulenspiegel
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Hi Andrew, it is not a common practise to return the screen grid decoupling capacitor to the cathode of the valve. No doubt there is a reason for doing this. The potential between the screen grid and cathode will stable.  My take on this arrangement is that it forms a cancellation circuit to correct the shape of the waveform.  Something similar can be found in some audio amplifiers.

Till Eulenspiegel.

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Topic starter Posted : 09/05/2019 9:00 pm
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Till Eulenspiegel
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In the KB PV70 and PV100 large screen TV sets the frame timebase  employs a variation on the screen grid decoupling arrangement in the Pye CTV.

In the KB the HT supply decoupling capacitor C92 is connected to the cathode of the output valve and the screen grid decoupling capacitor C94 to chassis.

Till Eulespiegel.

KB PV70FTB
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Topic starter Posted : 10/05/2019 8:51 am
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