It is currently Sun Dec 17, 2017 2:33 pm

Pye 405 line CTV.

 
Posts: 3712
Joined: Sun Feb 12, 2012 7:43 pm
Location: North Hykeham, Lincolnshire and Ilford, Essex (but not for much longer ...!)

Re: Pye 405 line CTV.

Post by Terrykc » Thu Jan 14, 2016 11:46 am

nuvistor wrote:Something about n +0.5 multiple of the line frequency to help reduce the dot pattern in an NTSC system  ...
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.
The NTSC subcarrier was 262.5Fh which gave a 180° phase difference on alternate lines so that the subcarrier dot pattern cancels out when viewed at a normal distance.

However, this doesn't work with PAL because the phase inversion of one of the quadrature modulated signals effectively causes a swing of ±90°on alternate lines.
Last edited by Terrykc on Thu Jan 14, 2016 12:02 pm, edited 1 time in total.

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 14, 2016 11:58 am

The sync pulses are locked to the master oscillator which is operating at a frequency 2X the sub carrier (2fsc = 5,315,625c/s) The output from the oscillator is divided by 525 to produce the twice line frequency for the frame sync pulses. (20,250c/s) Further division by two produces the line sync.
The output from the master oscillator is divided by two by a separate circuit to produce the correct sub carrier frequency.

So it follows the colour sub-carrier and the sync and blanking pulses are locked together. The master oscillator must be maintained in a frequency stable state.

Till Eulenspiegel.

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 14, 2016 12:40 pm

A pair of Marconi sub-carrier crystals for 405 line colour TV.

Till Eulenspiegel.
Attachments
000_1205.jpg

 
Posts: 489
Joined: Tue Mar 24, 2015 12:01 am
Location: Wigan

Re: Pye 405 line CTV.

Post by nuvistor » Thu Jan 14, 2016 2:48 pm

Thanks to all for the explanation, it is coming back to me, quite slowly, many years since I did any CTV theory.

Frank

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 14, 2016 4:28 pm

Hi Frank,
got to admit I've got pretty rusty on colour TV theory. From the 1980s single chip decoders became the norm. Decoder faults became less frequent. Seems that a lot of swotting up is required.
Generating colour bars for the 405 line system: Many years ago I assembled an encoder for 405 colour. The chosen chip for the job was the Motorola MC1377. Just a few component values needed changing from the published notes in order the chip would work on 405. In this chip the burst gate is achieved by generating a ramp waveform after the line sync pulse. Two comparators inside the MC1377 set the position of the burst gate. An external gate pulse facility exists for much more accurate timing.
The MC1377 accepts RGB drives.

Till Eulenspiegel.

 
Posts: 489
Joined: Tue Mar 24, 2015 12:01 am
Location: Wigan

Re: Pye 405 line CTV.

Post by nuvistor » Thu Jan 14, 2016 5:38 pm

This is from the Westinghouse colour training manual published 1954. It show a similar free running subcarrier osc.
web site http://www.earlytelevision.org/tv_schem ... color.html in the Westinghouse section.
Attachments
image.jpeg

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 14, 2016 6:21 pm

Hi Nuvistor,
The Westinghouse sub-carrier oscillator circuit is very similar to the one employed in the Pye. The Pye uses the PCF80 as the reactance valve and oscillator. 6U8 = ECF82 in Europe. Noted the Pye sub-carrier oscillator like the Westinghouse oscillator does not use a crystal.
Two 6BY6 heptodes employed as the R-Y and B-Y demodulators.
http://www.radiomuseum.org/tubes/tube_6by6.html

Till Eulenspiegel.

 
Posts: 847
Joined: Wed Nov 16, 2011 8:11 pm
Location: Cheltenham

Re: Pye 405 line CTV.

Post by Doz » Thu Jan 14, 2016 10:34 pm


 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Thu Jan 14, 2016 11:18 pm

Hi Doz,
Thanks for the link. I've added the coils to my watch list. This evening I removed the scanning coils from the neck of the CR tube in order to trace out the leads to the main chassis. Now the next stage of the fault finding procedure is to trace the connections from the octal scan coil socket to the secondary of the frame output transformer. Of course it is not that easy because the convergence circuits are in series with the scanning coils and the transformer.
There are three lead out wires from the frame scan coils. The two sections are wired in series giving a total resistance of 54 ohms, each section is 27 ohms so we can assume the coils are in balance. I discovered that the "centre tap" does not connect to any symmetry control, simply to a pair of 1.8Kohm damping resistors. The two scan coil leads disappear into the convergence control unit. Some time ago I thought I had got lucky because it was discovered that there is a 2000 microfarad reversible electrolytic capacitor in series with the frame scan coils, and it was low capacitance!
A pair of 4700mfd capacitors wired back to back are used to replace the faulty capacitor. The result.... no improvement whatsoever.
So tomorrow it's out with the main chassis so that the frame and convergence circuits can be examined.

Till Eulenspiegel.

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Fri Jan 15, 2016 1:53 pm

The main chassis is removed so that the frame timebase circuits can be examined.
Check out the construction quality, they weren't messing about with prototype lash ups when this set was constructed.

Till Eulenspiegel.
Attachments
000_1206.jpg
000_1207.jpg

 
Posts: 489
Joined: Tue Mar 24, 2015 12:01 am
Location: Wigan

Re: Pye 405 line CTV.

Post by nuvistor » Fri Jan 15, 2016 5:43 pm

yes very well made for a prototype. I did not realise , i thought the chassis was at the bottom of the set but it appears as though it is vertical on the left hand side looking from the front.
Luminance delay line stretched across that octal socket?

Frank

 
Posts: 2986
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Pye 405 line CTV.

Post by Katie Bush » Fri Jan 15, 2016 9:57 pm

Wow! twenty six valves, and then however many there are hiding under the 'tin shed'... What's the total valve count in that set?

Marion

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Fri Jan 15, 2016 10:51 pm

Hi Marion,
eight valves reside in the cage. 2 PL36, 2 PY81, 3 DY86 and the 6BD4 shunt stabiliser tube.

The thirteen channel tuner unit is out of the VT17 and early Pye Continental. Usual 1950s valves, PCC84 and PCF80.
Three stage vision and sound IF amplifiers using EF80 pentodes, almost the same circuit as the VT17.
Been working my way through the frame output stage and frame TB derived convergence circuits.
The scanning coils are connected direct to the frame output transformer. One of the dual concentric convergence controls was found to be faulty. The wiper was not making contact with the resistive track. A squirt of switch cleaner and also that trick of heating up the tags repaired it. The control has now got very low resistance readings at the rotational limits.
The PL82 frame output valve has a 390 ohm cathode bias resistor, it is shunted by a 4microfarad capacitor. Another capacitor is connected to the cathode of the PL82. this 100mfd capacitor is in series with the convergence controls. I'm sure it is in this part of the circuit where the frame linearity fault lies.

Till Eulenspiegel.

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sat Jan 16, 2016 1:08 pm

I expect the frame timebase derived convergence circuit to resemble my rough sketch as shown in the attachment.
Parabolic and sawtooth waveforms are added to produce the raster correction waveforms in the convergence coils.

Till Eulenspiegel.
Attachments
000_1208.jpg

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sat Jan 16, 2016 4:31 pm

nuvistor wrote:Luminance delay line stretched across that octal socket?
Frank

Hi Frank, The chassis is installed vertically on the left side of the cabinet.
The original luminance delay line is faulty so the delay line you see in the picture is one that was removed from a BRC 3000 decoder. The original Pye luma delay line was a very long device being more than twelve inches long, hence the length of the co-ax cable.
I've removed a delay line from a scrap Decca CTV25 chassis. This part will be fitted because it looks the part in this early set.
A typical 1967 colour set uses a BC107 type of transistor as the luma delay line driver. The Pye gets by with something much bigger, a PL83 valve.

Till Eulenspiegel.

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sat Jan 16, 2016 8:06 pm

The circuit of the sub-carrier generator. Pin 3 of the double triode goes to the colour lock control on the front panel. The oscillator is frequency and phase is controlled by a double-diode discriminator network using an EB91.

Till Eulenspiegel.
Attachments
000_1209.jpg

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 17, 2016 6:25 pm

Still working on the set to get it ready it for the newspaper article. This workshop is freezing. Circuit diagram of one of the final stage video amplifiers. Three identical amplifiers for R G B
The valve is a PCF80. The method of video black level clamping is by sync tip. The sync pulses are preserved into the three colour amplifier stages. Maybe not a good idea. Could be room for improvement here.

Till Eulenspiegel.
Attachments
000_1210.jpg
000_1210.jpg (117.04 KiB) Viewed 1169 times

 
Posts: 489
Joined: Tue Mar 24, 2015 12:01 am
Location: Wigan

Re: Pye 405 line CTV.

Post by nuvistor » Sun Jan 17, 2016 7:09 pm

This workshop is freezing.
All the incentive to get the set working, with all those valves it should soon warm the place up.

Sorry could not resist.
Frank

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 17, 2016 7:16 pm

All thirty-seven of them!

Till Eulenspiegel.

 
Posts: 2986
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Pye 405 line CTV.

Post by Katie Bush » Sun Jan 17, 2016 10:34 pm

Till Eulenspiegel wrote:All thirty-seven of them!

Till Eulenspiegel.



Hmm,

Does it toast both side of the bread at the same time?

 
Posts: 1553
Joined: Thu Aug 30, 2012 6:43 pm
Location: Wakefield, West Yorkshire.

Re: Pye 405 line CTV.

Post by marc » Sun Jan 17, 2016 10:37 pm

Katie Bush wrote:

Hmm,

Does it toast both side of the bread at the same time?

It should do the whole flipping loaf Marion ! :bba

Marc.

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Sun Jan 17, 2016 11:23 pm

As mentioned earlier in this topic I want to tough out this set as quickly as possible. The set has been in my possession for almost fifteen years and from time to time jobs do get done on it but now it's time to see just what this unique set is really capable of doing. Aurora have made a few special NTSC 405 line converters to produce the correct signals.

To wise up on NTSC television last year I purchased a very useful book entitled "Color Television FUNDAMENTALS" . It covers all the principles of the NTSC system, it's proving useful for the Pye restoration job. Also helpful is the circuit diagram of the RCA 21CT55 which uses the CTC2A chassis, a development of the famous RCA CT100.
The Pye has some elements of the CTC2A in it.

Sure enough the Pye with it's thirty-seven valves makes an useful room heater, but but when it comes to tube count it's easily beaten by the CBS model 205 with it's forty-five tubes!

It might be a good idea to search ebay.com to find out if a modern NTSC pattern generator can be bought. One that produces the correct I and Q bars.

Till Eulenspiegel.

 
Posts: 2665
Joined: Sun Sep 01, 2013 6:19 pm
Location: Behind the sofa

Re: Pye 405 line CTV.

Post by Cathovisor » Mon Jan 18, 2016 9:27 am

Find yourself a Tektronix TSG95 - a hand-held PAL/NTSC signal generator with all the superlative quality that the name Tektronix implies. Sold here in the UK. Or, a TSG-130A.

TSG-130A for sale here, one of many!

Another good book on the NTSC standard is the Tektronix guide - the one with the silver cover.

 
Posts: 847
Joined: Wed Nov 16, 2011 8:11 pm
Location: Cheltenham

Re: Pye 405 line CTV.

Post by Doz » Mon Jan 18, 2016 6:25 pm

Would the test card DVD not do with it's output set to NTSC?

That caused me a major headache when I did my Keracolor, because the output had defaulted to NTSC!

 
Posts: 2839
Joined: Tue Jul 26, 2011 5:30 pm
Location: Gateshead

Re: Pye 405 line CTV.

Post by Till Eulenspiegel » Mon Jan 18, 2016 6:57 pm

Well there is a good number of NTSC color pattern generators on ebay.com. A 525/60 line NTSC DVD would be OK if it could be possible to convert that standard to 405/50 NTSC. I reckon it should be possible to use the standard colour bars for setting up the Pye.
The I and Q signals operate on a different axis to the familiar R - Y and B-Y axis.

Todays work tracing out the convergence circuit more or less confirms that the circuits are not all that different from the hybrid CTVs made ten years later.

Till Eulenspiegel.

PreviousNext

Return to Colour Television



Who is online

Users browsing this forum: No registered users and 1 guest