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Old 16th Nov 2007, 10:22 pm   #1
FERNSEH
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Default 405 colour on my Pye CTV

At last I've ordered a 625PAL to 405NTSC converter from Darryl (tubesrule)

So as long as the 1956 Pye colour TV set is OK and has not gone the way of my RCA CTC7 I will be showing the results on this forum.

DFWB.
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Old 18th Nov 2007, 12:17 am   #2
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Default Re: Coming soon: 405 colour on my Pye CTV

The Pye CTV has always had a frame timebase fault, displaying compression at the bottom of the picture. Various frame output transformers have been tried with little or no improvement. Also, there has been just sufficient vertical scan to fill the screen. I've always suspected that the fault is between frame output transformer secondary and the scanning coils. The set has a lot of RCA CTC2B DNA in it, the colour decoder is similar and so is the frame output stage. Like the CTC2B the Pye employs a vertical centering choke which is associated with the vertical shift control. A non-polarised 1000microfarad capacitor is connected between scanning coils, the centering choke and the secondary of the frame output transformer.
This capacitor has gone low capacity. I've replaced it. I'll report the results of this evenings work tomorrow.

DFWB.
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Old 18th Nov 2007, 11:28 pm   #3
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Default Re: Coming soon: 405 colour on my Pye CTV

Quote:
Originally Posted by FERNSEH View Post
The Pye CTV has always had a frame timebase fault, displaying compression at the bottom of the picture. A non-polarised 1000microfarad capacitor is connected between scanning coils, the centering choke and the secondary of the frame output transformer.
This capacitor has gone low capacity. I've replaced it. I'll report the results of this evenings work tomorrow.
I reinstalled the chassis this evening. As I operate a policy of Glasnost I can report that there is no improvement to the frame linearity.
However, the set is displaying the R T Russell test card in colour.

DFWB.
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Old 26th Nov 2007, 9:18 pm   #4
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Default Re: Coming soon: 405 colour on my Pye CTV

OK Folks,
I've got the converter and have bought a new digi camera from ASDA so it can't be long until the Pye is displaying TV program pictures for this forum.
Think about it, it'll be nearly fifty years since this set last displayed proper program material.

DFWB.
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Old 27th Nov 2007, 9:27 am   #5
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Default Re: Coming soon: 405 colour on my Pye CTV

Excellent news David!
I am waiting in great expectation to see the results.
Today I will spend a little time on my conversion, but I will report back on my own thread.
This is great news that the old prototype NTSC system has now got two sets running in the UK and showing good watchable everyday programs.
We now need to help out Andy Green with a set!
well done
Trevor
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Old 27th Nov 2007, 8:46 pm   #6
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Default Re: Coming soon: 405 colour on my Pye CTV

Here are two pictures from the screen of the Pye CTV.
The luma delay line is absent from the circuit so it will be noticed that the chroma and luma are not coincident.

DFWB.
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Old 27th Nov 2007, 9:23 pm   #7
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Default Re: Coming soon: 405 colour on my Pye CTV

Amazing pictures David, especially considering the age of the set. I always think that the colour on these old tubes has a different quality to more modern ones - probably due to the phosphor composition. Good work!
I am getting an ATV transmitter together and ordering a VSB filter shortly, so that at least I can be ready to transmit 405 line NTSC. www.Hamtv.com in the USA does a 70cm to chA3 downconverter, which might be useful, so I am getting one of these to try too.
Eventually, I hope to arrange a sked with someone else with a 405 line (B/W) set to test the viability and range of som System A transmissions. If I bring it all up nearby Mt Leinster (3000ft near the east Coast) there is a good chance of making it to Wales.
One day I hope that we can eventually TX and RX 405 line NTSC over a reasonable distance!
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Old 28th Nov 2007, 9:49 am   #8
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Default Re: Coming soon: 405 colour on my Pye CTV

Excellent results David, I wonder if the quality of pictures are better now than in the 50's. Darryl's converters are truly wonderful and no doubt the broadcasters would have used them for standards conversion if we were still running two systems.
My set is complete but takes up too much room in the shed so it will be upstairs in the house after Christmas.
Well done and "Power to 405 line NTSC"!
Trevor
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Old 28th Nov 2007, 10:29 am   #9
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Default Re: Coming soon: 405 colour on my Pye CTV

Quote:
Originally Posted by murphyv310 View Post
I wonder if the quality of pictures are better now than in the 50's.
I'm sure they are. In the 1950s the available picture sources were nothing like as good as now. A flying spot slide or film scanner of that period might just about have equalled a modern one but modern cameras will be much better. Also there are no "off air" degradations. I know that modern kit is often used badly and now we contend with compression artefacts but that isn't the point.

The weakest link in the 405 NTSC chain is now the receiver. Any improvements there will be rewarded with better pictures.

Congratulations to both of you for making 405 NTSC live again. And of course to Darryl for making it possible to experiment with 405 NTSC without designing your own converter. David Robinson's converter (a "one off" with no intention to make more) produces 405 NTSC but AFAIK it has never been displayed on a colour set.
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Old 28th Nov 2007, 12:20 pm   #10
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Default Re: Coming soon: 405 colour on my Pye CTV

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Originally Posted by ppppenguin View Post

The weakest link in the 405 NTSC chain is now the receiver. Any improvements there will be rewarded with better pictures.
There is still a lot of work to do on the Pye. I fact since the first pictures were taken two days ago the performance of the colour decoder has deteriorated.
The colour decoder is similar to the RCA CT100 and 21CT55. The colour demodulators employ two 6BY6 hexode valves and operate along the I and Q axis. Also, like the American sets the RGB drives are supplied to CRT control grids. PCF80 valves are used as the amplifiers and crystal diodes serve as the clamps. The three CRT cathodes are connected to a fixed potential and the frame blanking pulse.
The original 405 NTSC system had different bandwidths for the I and Q colour signals The Q signal had a bandwidth of only 300Khz and the I signal was 1Mhz. Later sets operated the demodulators along the X and Z axis.

Anyway, according to my policy of glasnost here are two recent pictures.

DFWB.
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Old 28th Nov 2007, 2:08 pm   #11
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Default Re: Coming soon: 405 colour on my Pye CTV

Congratulations David! The set looks wonderful. It has that same look as early phosphor color sets here. I was very nervous about the converters working as I had no way to visually verify them. I programmed them for 525 NTSC to make sure they worked, and then just switched them over to 405 NTSC timing and hoped for the best. Now that you and Trevor have your sets running, I can breathe a sigh of relief

Again, well done to both of you.

Darryl
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Old 1st Dec 2007, 11:25 pm   #12
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Default Re: Coming soon: 405 colour on my Pye CTV

Hi Trevor,
I have that spare CTC7 chassis. The line output transformer is missing so a special one will have to be made for 405 lines. The decoder will require a few changes, the first thing to do is change the sub-carrier oscillator from 3.58 to 2.66Mhz. The chassis could be modified to become a baseband monitor.
The chassis came with the scan coils and convergence unit. The CRTs required are the round 70 degree 21CPY22, 21FBP22 or the Mullard/Philips AX53-14. All are difficult to find in the UK and Europe.

The easy bit is the construction of a cabinet.

Could be a project when the shop closes down.
DFWB.
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Old 5th Dec 2007, 12:26 pm   #13
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Default Re: Coming soon: 405 colour on my Pye CTV

A replacement luma delay line has been fitted and now the chroma and luminance are coincident.
The original delay line had failed during the previous ownership. The replacement part was removed from a BRC 3000 CTV.
The original delay line is 59cm long, the replacement is only 14cm long.
The luma delay driver is a PL83 video pentode, no puny BC108 transistors in this set.

DFWB.
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Old 6th Nov 2017, 5:09 pm   #14
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Default Pye 405 line colour TV. Frame timebase issues.

The Pye 405 line colour set has always had bad frame linearity. The sawtooth drive to the grid of the PL82 frame valve has perfect linearity and amplitude. A series of tests have been carried out to determine if the fault lies in the secondary circuits of the frame output stage, for example the path of the sawtooth drive from the output transformer through the convergence network, no faults found. I did think I'd got lucky when the 2200uF capacitor in the vertical picture shift circuit was found to be of low capacity, replacing it made no improvement. I'm absolutely certain that scanning coils are OK. Now I have other ideas on how to solve the problem.
Talking to Mike (Mikey405) about this on going fault we consulted the circuit diagram of the Ekco round CRT colour set which was made in the early sixties.
The CT100 employs an ECL85 as the frame oscillator and output valve. What was noted is that although the screen grid of the pentode section is supplied from the 200 volt HT supply the anode is supplied from the 360 volt HT line which also supplies the line output stage. Now this begs the question: in the Pye CTV should the PL82 frame output valve also be supplied from the 360 volt supply? Both sets employ a voltage doubler to supply 360 volts to the line output stages. Examination of a 1950s CBS colour TV circuit revealed the same thing, the 6BL7GT frame output valve also receives it's HT from a much higher voltage B+ source, 400volts in the American receiver. So now the Pye CTV will be reassembled and voltage measurements carried out on the frame output stage. As far as I can remember the frame output stage receives it's supply from the 200 volt HT line.
The absolute highest voltage supplied to the anode to the PL82 is 550V, so there is no doubt the valve should with stand 350 volts or so on it's plate. Let's find out if that is so.

DFWB.

Last edited by Station X; 6th Nov 2017 at 5:28 pm. Reason: Threads merged.
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Old 6th Nov 2017, 8:53 pm   #15
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Default Re: 405 colour on my Pye CTV

Circuit diagram of the frame timebase in the Ekco CT100.
Note the 360volts anode supply for the ECL85.

DFWB.
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Old 7th Nov 2017, 9:13 am   #16
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Default Re: 405 colour on my Pye CTV

Hi David,
Well that is interesting!! As far as I was aware, The BBC was considering the use of NTSC in the early '60's, but I didn't know that anyone in the UK was doing anything as far back as '56.
Is this a UK production set or a prototype? In the event, it would have been totally obsolete by the time colour actually started in (I believe) 1967!
It would be great to have some more details/ pictures etc. of the set or a link to an old thread if you've already done that. Circuit details would also be very interesting.
Good Heavens, colour in 1956: whatever next!!
All the best
Nick
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Old 7th Nov 2017, 9:17 am   #17
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Default Re: 405 colour on my Pye CTV

Some information and a colour page from Picture Post 1954.
http://www.earlytelevision.org/british_ntsc_color.html
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Old 7th Nov 2017, 9:28 am   #18
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Default Re: 405 colour on my Pye CTV

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Is this a UK production set or a prototype?
I'm sure David can confirm, but I believe it was a prototype - and as such is extremely rare (and probably unique as a working example). I believe the Media Museum in Bradford has all or most of another set, but not in working order.
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Old 7th Nov 2017, 9:33 am   #19
ctc15
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Default Re: 405 colour on my Pye CTV

Hi David
In the Colour television book by Carnt & Townsend the G.E.C TTIV 405 line colour TV field time base shown on page 314 has a HT of about 390v and it to has a PL82 (N329) I think increasing the HT may be the Answer.
Thanks
Keith
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Old 7th Nov 2017, 9:38 am   #20
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Default Re: 405 colour on my Pye CTV

Wireless World produced an article in which an experimental design to receive the BBC 405 NTSC colour transmissions was discussed.

Wireless World March 1956 page 112 and April 1956 page 183.

Copies of Wireless World can be downloaded from the Americanradiohistory web site here.
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