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Pye 405 line CTV.

 
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Re: Pye 405 line CTV.

Post by Cathovisor » Fri Jan 08, 2016 8:10 pm

peter scott wrote:If you present YouTube with 4:3 material they do appear to present it more of less correctly but the BBC appear to be making a similar mess of 4:3 in recent times:
http://www.vintage-radio.net/forum/show ... p?t=122305

Peter

"You are not logged in or you do not have permission to access this page" ??

 
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Re: Pye 405 line CTV.

Post by nuvistor » Fri Jan 08, 2016 8:15 pm

10 posts required and be logged in to access that part of the site.
Frank

 
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Re: Pye 405 line CTV.

Post by Cathovisor » Fri Jan 08, 2016 8:35 pm

Okay; not a member, so...

 
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Re: Pye 405 line CTV.

Post by peter scott » Fri Jan 08, 2016 9:07 pm

Sorry, I won't reproduce the full thread. My initial post was:

Have just been watching a program about the Two Ronnies including lots of clips from their shows. These almost all date from the pre-widescreen era so the BBC fills the 16:9 with a full height image with static filler strips where you might expect to see black areas but do they present the vintage material with correct 4:3 format? No, for some strange reason they display it as 5:4 format making everyone look a little skinny!

Why?

Peter


After some slightly wandering discussion I posted:

I too have seen the BBC transmit 16:9 displaying a 4:3 image correctly with black bars so they can do it.

I just cannot understand why they choose to display 4:3 material as 5:4.

Perhaps it is pure ignorance or perhaps it is deliberate distortion of older material a bit like the nasty habit of adding noise or fake film scratches or strange colour casts.

Peter

 
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Re: Pye 405 line CTV.

Post by ntscuser » Fri Jan 08, 2016 10:54 pm

Rebel Rafter wrote:The power consumption must've been phenomenal with a 50mm neck and all valves and I thought the B&O 3400 was high on power at 360w. How much power did these sets use?


Not as much as you think as the tube has a 70 degree scanning angle compared with the B&O's 110 degrees. The average power consumption for this kind of set was 350 watts.

 
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Re: Pye 405 line CTV.

Post by Katie Bush » Fri Jan 08, 2016 10:57 pm

That compares well with the the good old G6, weighing in at a healthy 500W! - No need for central heating in that room. :aa

 
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Re: Pye 405 line CTV.

Post by ntscuser » Sat Jan 09, 2016 1:11 am

Forgot to mention, B&O made a 'roundie' colour set as well in 1963, 625-lines of course and probably PAL:

Image

 
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Re: Pye 405 line CTV.

Post by Bobhowe » Sat Jan 09, 2016 11:17 pm

Been to see this wonderful set today at Davids shop the build quality of this set is amazing considering it was an experimental set 60 years ago . Judging by the valve & component line up it would warm the room it was in took some photos will up load them soon :bba

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 10, 2016 12:25 pm

The Pye 405 colour set has two heater chains so that's 0.6amp drawn from the mains. 144watts! I'll count the valves later today, we do know that there is eight in the line output cage. Two PL36, two PY81, three DY86 and one 6BD4 stabiliser tube.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_6bd4a.html This tube is similar to the ED500/PD500.
The EHT shunt stabiliser tube and CRT heaters are supplied from a mains transformer.
Under conditions of zero beam current in the CRT the shunt stabiliser will dissipate over 20watts. The anode can glow dull red.
There is a good deal of crystal diodes in this set, in fact there are no EB91 double diodes anywhere on the chassis.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by nuvistor » Sun Jan 10, 2016 1:42 pm

The Pye engineers obviously had their reasons but I would have thought it would have been simpler for them to use valves from the USA that had been designed for the extra scanning/EHT power required for a CTV tube.
If it is possible to get it working I am sure you are the one to sort it out, I would have given up before starting.

Frank

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 10, 2016 2:09 pm

Hi Frank,
I believe it was policy in those times to use as many UK sourced parts as possible. In the Pye the CRT and it's scanning components were supplied by an US maker which was most likely to have been RCA, quite simply no UK manufacture made these components at that time. The CRT mask was also supplied by an US firm. Philips in Holland might have started making colour CRTs in 1961/62, perhaps earlier?
Some elements of the Pye receiver's circuit originated from the 1955 model VT17. The tuner and IF amplifiers , also the line oscillator and frame timebase.
The experimental Bush colour set employed a pair of PL300 valves for the line output. The set was designed as a 625 line receiver from outset. Confirmation required for that fact.
Murphy made a 405 line colour receiver. Also Ekco before the company was taken over by Pye.
An article about the GEC TT4 can be found in the Practical Television magazine.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by nuvistor » Sun Jan 10, 2016 4:02 pm

Till Eulenspiegel wrote: I believe it was policy in those times to use as many UK sourced parts as possible.
Till Eulenspiegel.

Import taxes were probably prohibitively high.

I can understand the RF/IF sections using tested UK designs but refined to reduce phase distortion and adequate band width. The UK and USA RF/IF sections needed different criteria, I don't mean frequency/bandwidth but the USA sets needed to have good sensitivity with good intermodulation characteristics, i.e. the set had to perform well in deep fringe as well as large conurbations that had many stations filling up the VHF bands. UK sets generally required just good sensitivity as the transmitters were few and far between and even then some TV's were not as sensitive as others.

I had not heard of the PL300, I have been out of the trade so long I have lost most of the knowledge.

Frank

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 10, 2016 4:46 pm

The PL300 was developed in France by Fivre in 1961. Mullard marketed the valve in the UK. That's why I believe the Bush colour set which uses the PL300 is a 625 receiver. By that time we all knew the game was up for 405 and any further development of a colour TV system using the old line standard. The future was 625.

The PL300: http://www.radiomuseum.org/tubes/tube_pl300.html

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Rebel Rafter » Sun Jan 10, 2016 8:14 pm

Hi, from RR. What sort of EHT system did these old 405 colour sets have? did they have a multiplier using DY86's or something similar or did they have a full overwinding like some later colour sets? Did any of them have a LOPT in a can of oil like on the old Murphy "oily beasts"? What sort of EHT voltage did they use? RR.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 10, 2016 8:37 pm

Hi RR, The Pye 405 line colour set we are discussing employs three DY86 diodes in what is not strictly a double circuit. The EHT over winding on the transformer provides 17KV which is augmented from the 6KV pulse present at the anodes of the two PL36 output valves to produce 23KV. It's the same arrangement is used in the RCA 21CT55. The 21CT55 was developed from the CT100, the first RCA colour TV.
EHT boosters were used on much earlier sets. For example the post war HMV model 1804. When it came to replacing the original Emiscope 3/4 CRT, the TA10 was the replacement. This tube required more EHT, the mains transformer supplied only 4KV. The answer was an EHT booster which used the 1-5KV pulse present at the anode of the line output valve to augment the existing 4KV. You got 5 to 5.5KV.

I'm certain that the DY86 valves are really not up to the job. Maybe something more like this: http://www.radiomuseum.org/tubes/tube_3a3.html Used in American colour TVs.
The DY86: http://www.radiomuseum.org/tubes/tube_dy86.html
The DY802 could be considered.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Wed Jan 13, 2016 6:41 pm

This rare set is going to receive the attention it deserves. the cabinet was re-polished in the summer of 2012. This may be regarded an experimental set but as you can see the veneers are properly book matched and the surface finished to a high standard. It's likely these sets were installed in the houses of TV executives so had to look at least presentable. Not constructed from old orange boxes and angle iron.
Todays job was to attend to the front pre-set controls access door. It was badly scratched. The old lacquer has been removed with a scraper, the correct wood stain applied and finally re-polished. It looks a lot better now.

The Scottish Sunday Post newspaper have expressed an interest in the set as the subject of a special article. Let's present the set as the oldest working colour set in the UK.
I have to thank Jon for contacting the lady from the paper who is handling the article.

Till Eulenspiegel.
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Re: Pye 405 line CTV.

Post by Michael Watterson » Wed Jan 13, 2016 8:02 pm

Under conditions of zero beam current in the CRT the shunt stabiliser will dissipate over 20watts. The anode can glow dull red.


X-rays? 23KV?

 
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Re: Pye 405 line CTV.

Post by nuvistor » Wed Jan 13, 2016 8:39 pm

The controls, at the top I can see Hue and saturation but cannot make out the centre top control label,, probably should know it but, well you know how it is.

 
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Re: Pye 405 line CTV.

Post by Cathovisor » Wed Jan 13, 2016 8:51 pm

Alarmingly, it says "hold" :ccf

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Wed Jan 13, 2016 9:30 pm

The colour sub-carrier does not employ a crystal, it's a free running oscillator which is locked to the burst by means of a two diode discriminator . I have the circuit somewhere. When I back to the shop I'll check the title the colour sub-carrier frequency control.
X-rays? The max EHT is 23KV and as a shunt stabiliser tube is employed I reckon there is a risk of exposure to X-rays from that device.
Fortunately the 6BD4A is housed in a cage along with all the other line output stage components. The 6BD4A can glow dull red under zero CRT beam current conditions.
I'm going to tough out that frame timebase fault. The frame scanning coils are wound in two sections. There is a common connection and the other two leads will most likely be connected to a balance control which will function as the red-green symmetry control. It's most likely that the control is located on the front panel.

Till Eulenspiegel.

 
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Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 14, 2016 12:32 am

Close up picture of the those colour controls. The hue control knob and it's shaft has been removed to allow servicing work to be carried out around the sub-carrier generator.
I'd imagine the reason for the variable colour hold control was to allow different sub-carrier frequencies to tried out until the final figure was determined.

Till Eulenspiegel.
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Re: Pye 405 line CTV.

Post by ntscuser » Thu Jan 14, 2016 2:28 am

The quality of the screen-printing on that panel suggests that quite a few were made. They would hardly have gone to all that trouble for a one-off prototype of two.

 
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Re: Pye 405 line CTV.

Post by nuvistor » Thu Jan 14, 2016 9:36 am

Thanks for the info and extra photo, that makes more sense now. I wonder if the transmission subcarrier on the experimental transmission was not that stable or has ntscuser says perhaps it was moved around slightly to test dot interfence on BW sets. Something about n +0.5 multiple of the line frequency to help reduce the dot pattern in an NTSC system but I think that was modified for the 405 CTV, but not sure.
Was it n+ 0.75 line frequency for our 625 PAL system making the dot interference more noticeable on the PAL system. I cannot remember why the change though.
Sorry bit of a waffle.
Frank

 
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Re: Pye 405 line CTV.

Post by Cathovisor » Thu Jan 14, 2016 9:46 am

nuvistor wrote:Was it n+ 0.75 line frequency for our 625 PAL system making the dot interference more noticeable on the PAL system. I cannot remember why the change though.

Fsc = (283.75Fh + 25) Hz.

 
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Re: Pye 405 line CTV.

Post by Michael Watterson » Thu Jan 14, 2016 10:10 am

ntscuser wrote:The quality of the screen-printing on that panel suggests that quite a few were made. They would hardly have gone to all that trouble for a one-off prototype of two.

Is it screen printing or template engraved + filled?

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