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Pye 405 line CTV.

 
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Re: Pye 405 line CTV.

Post by ntscuser » Mon Jan 18, 2016 7:12 pm

You want one of these! :bba

Image

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 18, 2016 7:39 pm

Now that's more like it. And it will be nice and warm in there what with all those valves glowing nicely. Better than this workshop I'm at the moment.
Pictures of the convergence coils. As you can see they don't differ much in principle to the later coil assemblies used in the CTVs we are more familiar with.
The coils have even been assigned a Pye part number: 670442. Made by the Glaser-Steers Corporation.

Till Eulenspiegel.
Attachments
000_1211.jpg
000_1211.jpg (112.86 KiB) Viewed 1714 times
000_1212.jpg

 
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Re: Pye 405 line CTV.

Post by Niall » Mon Jan 18, 2016 7:52 pm

ntscuser wrote:
Image


That's crying out for a caption :-)

 
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Re: Pye 405 line CTV.

Post by Briancuff » Mon Jan 18, 2016 8:14 pm

"I don't know what you mean, David. It's fine leaving here"!

 
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Re: Pye 405 line CTV.

Post by Cathovisor » Mon Jan 18, 2016 10:03 pm

Spoken like a true BBC Engineer!! :aaj

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 18, 2016 10:47 pm

Glaser Steers Corp made record turntables. Most common on was the GS77.
From the Radiomuseum: http://www.radiomuseum.org/r/glaserstee_gs_77.html

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Niall » Tue Jan 19, 2016 1:51 pm

Brianc wrote:"I don't know what you mean, David. It's fine leaving here"!


Voice on phone: "Have you tried switching it off and back on again?"

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Tue Jan 19, 2016 7:46 pm

I might have found the frame timebase problem. The Frame output transformer primary has a DC resistance of 190 ohms. The secondary has a tapped winding and has a total DC resistance of 284 ohms with the tapping at only 8.3ohms. The two sections of the scanning coils have a resistance of 27 ohms each. Although I haven't established if the coils are wired in parallel it most likely they are. So it might be possible the connections of the coils to the secondary of the transformer are incorrect. I find the scan coils are connected to the full 284 ohm winding, that can't be right surely? Later this evening I will return to my cold workshop and rewire the coils to the 8.3 ohm secondary winding.

The circuit of the line and frame picture shift network.

Till Eulenspiegel.
Attachments
000_1213.jpg

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Tue Jan 19, 2016 10:07 pm

This picture was taken many years ago. The compression at the bottom of the picture can clearly be seen.
This is the problem I'm currently trying to fix.
Link to the American radio history website: The February 1959 PT featured the GEC TT4 405 line colour TV set.
http://www.americanradiohistory.com/Arc ... 959-02.pdf

Till Eulenspiegel.
Attachments
PyeCTV.jpg

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Tue Jan 19, 2016 10:49 pm

News Flash!. I'm back in the cold workshop. Further examination of the frame output transformer reveals that the primary does not have a total resistance of 190 ohms. There is only the single secondary winding of 8.3 ohms. I will rewire the transformer and then let's see what happens when the chassis is refitted into the cabinet. That frame fault might finally be fixed at last.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by ntscuser » Wed Jan 20, 2016 4:45 am

Till Eulenspiegel wrote:Link to the American radio history website: The February 1959 PT featured the GEC TT4 405 line colour TV set.
http://www.americanradiohistory.com/Arc ... 959-02.pdf


One and thruppence? :ccf That's a twenty-five percent increase over the price in 1956! Talk about "Rip-off Britain", I shall be writing to my MP about this! :aah

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Wed Jan 20, 2016 5:50 pm

ntscuser wrote:One and thruppence? :ccf That's a twenty-five percent increase over the price in 1956! Talk about "Rip-off Britain", I shall be writing to my MP about this! :aah


Prices were rising but you could afford it because in the fifties we were told "you've never had it so good"

http://www.telegraph.co.uk/news/politic ... -boom.html

Anyway, I'm not having it so good. I'm wishing now I hadn't disturbed the Pye. Brian (Focus2) called around this morning to visit me and just in time to see the Pye fired up. Well, all we could get from the set was a rather dull raster, no sound or vision. Then I realised after the frame shift leads had been disconnected from the frame output transformer the HT voltage to the sound and vision IF amplifiers is reduced. After re-establishing the HT to correct voltage we were greeted with the same results. No sound and vision.
To compound the agony the PL36 line output valves started to glow red hot. Now we find one of two 47ohm resistors in series with the HT supply to the booster diodes has gone open circuit as a result of the excessive current demand from the line timebase.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by nuvistor » Wed Jan 20, 2016 7:46 pm

Hi Till,
If any one knows the answer you will.
The early 1950's colour CRT's had a red phosphor that produced only limited illumination, consequently the blue and green drives had to be keep lower to compensate. In the 60's new rare earth phosphors for red enabled much more illumination and the blue/green drives could be increased to match.

The new phosphor had a slightly different shade of red , were any changes in transmission/receiver setup required to accommodate the new colours?

When the UK started scheduled colour the new phosphors were already in use. On a slightly different topic the first dual standard sets had shadow masks designed for 525 lines and more troubled by moire patterns, than the later 22 and 26 inch CRT's, or that's what I was told by the manufacturers.
Frank
edit. just seen your last post. :zx:

 
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Re: Pye 405 line CTV.

Post by Doz » Wed Jan 20, 2016 8:20 pm

nuvistor wrote:When the UK started scheduled colour the new phosphors were already in use. On a slightly different topic the first dual standard sets had shadow masks designed for 525 lines and more troubled by moire patterns, than the later 22 and 26 inch CRT's, or that's what I was told by the manufacturers.
Frank


There's a bit in the GEC2028 manual about minimising moire, especially on 405

 
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Re: Pye 405 line CTV.

Post by Focus 2 » Wed Jan 20, 2016 10:41 pm

Indeed it was disappointing the Pye didn't function as we'd hoped. We heard faint test tone and bars on the unmodulated raster but unable to achieve a proper picture.
Hopefully this will be straightforward to rectify, removal of the chassis can easily dislodge a lead as we all know.
On the credit side, when the scanning lines were visible the linearity looked a lot better.

Here are a couple of pictures taken and uploaded with Till's kind permission.

Cheers,
Brian
Attachments
Pye 405-line CTV 1.jpg
First light in a while.
Pye 405-line CTV 2.jpg
After some adjustments of the front controls.
Pye 405-line CTV interior.jpg
Part of the interior with the set in operation

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 21, 2016 12:33 am

The reason for the two PL36 line output valves glowing red hot is because the line drive for the has failed. There is no HT supply to the PCF80 line oscillator. It should be a simple matter to trace the HT feed. The chassis will come again tomorrow.
Also, in due course that strange frame shift circuit will be replaced with something that resembles the shift circuit used in the Decca CTV25.
Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Fri Jan 22, 2016 9:49 pm

Servicing work on this set will restart over the weekend.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by ntscuser » Sat Jan 23, 2016 9:44 pm

In the meantime here's a link to Till's Pye at the Early Television Museum wesbite:

http://www.earlytelevision.org/pye_expe ... color.html

 
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Re: Pye 405 line CTV.

Post by ntscuser » Sun Jan 24, 2016 10:14 pm

This report details three different kinds of 405-line NTSC monitor built by the BBC in 1957:

R&D Report 1957-07 - BBC

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 25, 2016 3:52 pm

Very little progress over the weekend. The servicing work was restarted this morning. I hope to have some positive results later on today.
In a previous post I mentioned that I was not very impressed with the DC restorers employed in the final RGB amplifiers.
Clamping is achieved by using the sync tips which are preserved in a rather distorted form through the colour decoding process. So later on I intend to employ a back porch black level clamp circuit similar to the arrangement shown in the BBC push-pull video amplifiers. Anti-phase pulses will be generated to drive the two diode black level clamp.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 25, 2016 7:12 pm

The line timebase oscillator is working again so now the EHT is available. A bright raster is apparent on the screen.. So I'm back to stage before the line timebase failed. No sound or modulation on the screen.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Katie Bush » Mon Jan 25, 2016 9:10 pm

This is become like one of Chris' sagas.... :ccf

I've often wondered about the ancient Japanese Shinto, where it is believed that even inanimate objects have a soul (they certainly have presence and character!).. If it is, then this set has either, all the mischief of Till Eulenspiegel himself :aa , or the evil temperament of Beelzebub.. :aah

How much of the set will remain original after restoration?

Marion

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 25, 2016 9:19 pm

Hi Marion,
Well it seems the set didn't like having it's chassis removed. It's never been the right since.
I've traced the HT supply to the IFs and tuner. On switch on, the voltage at the smoothing choke is 275V. As the set warms up the HT voltage falls to a low value. Something is dragging it down.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 25, 2016 10:46 pm

21:46hrs. I'm back in the much warmer workshop. At last results! With the HT restored to the tuner and IF amplifiers sound and vision.
After removing the picture shift circuits there is much more spare height available but the linearity still could be better.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Tue Jan 26, 2016 11:22 am

Evidence of last nights work. A monochrome test card C with colour fringing.

Till Eulenspiegel.
Attachments
000_0231.jpg

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