UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)

- Vintage Television and Video (https://www.vintage-radio.net/forum/forumdisplay.php?f=37)

- - Pye V4 (https://www.vintage-radio.net/forum/showthread.php?t=155034)

I recently was kindly given a Pye V4 by Shaun of Rotherham. The set did produce a picture but was unstable and suffered a lot of interference on picture the width would decrease and lose both vertical and horizontal lock. On examination inside I discovered all the 3nF in the valve heater filter circuit had been cut out of circuit. Anyway to cut a long story short I must have replaced every 3nF capacitors in the set and every Hunts capacitors that I could find. I replaced those metal discriminator diodes with 1N914. I enclose a picture of the set below. I still have a couple of problems I need help in resolving. The set has some faint vertical striations on the LHS. If I increase the brightness the picture gets thinner and goes out of focus. (I have replaced the PY81, PL81 c106 and EY51). The boost voltage across C106 is around 450V but falls when brightness is advanced. The voltage on pin 10 of the tube is 220v, but that is with a 10Mohm DMM so it could be double this? I have read in earlier topics that the LOpT could need drying out could this be a cause? I have tried adjusting the horizontal drive preset whilst measuring the voltage across R126 the cathode resistor(PL81) but my meter just stays at around 5V. Suggestions from anyone will be welcome.

Hmmm.

I never realised those caps were missing. The set had been hacked around a bit when I got it and I've never had much time to deal with this set properly, though I knew it worked but with a few faults.

As I recall from the one (VT14 version) I had many years ago when I was a child - that too always pulled in the width a bit when the picture was very bright. - How much does the HT voltage fall by when the brightness is high ? Maybe that's just the way they behave. They were few and far between really even when I entered the TV trade as an apprentice service technician way back in 1973.

It reminds me a bit of the Pye CT200 18" colour set many years later in the early seventies, introduced to compete with the Japanese manufacturers. Engineers not familiar with this model would certainly be looking for faults, as they would see the picture bouncing around like crazy on flashing images, and defocussing on high beam currents. They'd be wasting their time because they were always like that straight out if the box brand new! I've not seen many V4/VT4s really but I always remember that on very high brightness settings they were a bit like you are describing here. Perhaps others here know them better and might wish to comment.

What's the HT voltage measure at high brightness compared to zero brightness ? If the HT falls too much, I'd check the PY82's and the smoothing etc. It is possible for the set to still run with one PY82 being low emission with the expected loss of performance. Of course when the HT falls, reducing the scanning drive, the EHT will fall too, and then the reduced EHT increases the picture size so there's some compensation effect there! Where the EHT source impedance/resistance is too high the picture balloons in all directions with increases in brightness, usually down to a low emission EHT rectifier. The theory here is that the electron beam is drawn more slowly towards the final anode because of the reduced EHT and therefore spends more time in the deflection area and is therefore more affected by it, so the size of the raster increases.

As for the striations - That's usually caused by ringing of wound components in the line output stage - this modulates the speed of the horizontal movement of the beam causing visible changes in brightness. The effect lessens as the beam traverses the screen because the ringing subsides. The line linearity coil on some sets has a damping resistor of about 1.5 K which goes often O/C and causes this, but I don't see one on this circuit. Is some minor stray ringing somehow modulating the video or signal stages I wonder ?

Well done for getting this set, and the Radio Rentals set working so well. I only wish I had had the time, and unfortunately I won't really have the room to keep all the sets when I move house, and giving some of them away to people who do have the time for them was the best choice I think.

Thanks for that Shaun. Most people would say the picture is good enough as it is. I remember my VT4 when I was around 10years old and it did give a good picture. You did say the tube was low, its now good after a bit of flashing! Yesterday I watched the movie "KingKong" on the set it goes on for around 3 hours. The picture was taken after this (TCC) and you can see the width and height have remained constant. The HT stays approx constant when the brightness is advanced.The picture does not ballon but goes narrower and out of focus! The boost drops so maybe its the LOpt having changed the components listed above.
Thanks again for the set.

Every version of the V4 and the later V14 series, plus a few more Pye models of this era all displayed the lack of width and defocusing effects when the brightness is set for a somewhat over bright picture. Nothing to worry about and your example looks great. John.

Unfortunatly the "good" picture did not last. Yesterday I had the TV on for over 3 hours and watched "The Rear Window" on C4. This afternoon I switched it on and no picture or raster and no EHT.
I am suspecting it is terminal for the LOpT Is my assumption correct? I have had an oscilloscope on the set.. The line oscillator (V26) ECL80 on pin 6 waveform 14 on circuit is exactly correct shape and amplitude.The same is on the other side of C98 feeding the PL81. Pin 8 on the PL81 waveform 16 on circuit diagram waveform correct but amplitude only 40v. I have replaces C105-106-107, to no avail. I have checked the line scan coil screened lead and that is OK (not S/C).
Both PL81 and PY81 have been changed. The EY51 leads are OK. I can get a feeble spark from the anode side. Am I missing something or is it the LOpT?

It doesn't sound good from what you've previously described.

If the set has been little used and kept in unheated surroundings for a long time then it shouldn't be run to any extent until the line tranny has been fully dried out. I always say that a set acquired around September after a long hot summer is likely to live if just run without much thought, and one acquired around March after a long cold winter is likely to not survive for long unless steps are taken regarding warming and drying the LOPT.

Let's hope it's not the line tranny, as it'll either need a rewind (if it can be done) or the set modifying to replace it with something else, as you'll not find a direct replacement now. Anyway, other than the tranny, faults like this are usually the boost capacitor leaking - have you replaced it, or is the replacement an old one from years ago?

Thanks for that. The one fitted (C106) that I removed whilst repairing the set was only 0.1uF I fitted two new 0.22uF in parallel (630V). I am going to put a request in for a LOpt.

Is it possible that the EHT rectifier heater winding is breaking down under load? You can check this by disconnecting the EHT rectifier heater leads and attempting to draw a spark from the ey51 anode.

Disconnect the scanning coils completely and double check the screened lead. It can break down with pulse voltage, The scan coils themselves may be faulty, S/C line to frame.
This was a very common fault when a cellophane sheet was used to insulate the windings.
Later types employed Polythene and were trouble free. If they are faulty, most PYE 70 degree coils can be fiddled to fit.
Disconnect the width coil as a final check. The V4 will work without it if you discover it is S/C.

A used LOPT will probably be little better than the one you have. A rewind will cure the problem permanently. Regards, John.

Thanks Laurdys and John. I will have a go this weekend all that you have suggested and will report back.

Picture looks pretty good to me. Repaired a fair few of those in the '50s. Pig to get the EY51 out - and in again.

Peter

Lovely to see a working Pye V4 when I joined the trade in 1961 there was a Pye v4 in the workshop and the service manager said I could have it !
So I got it going and it was in my bedroom for many years.
Happy days !

I have spent most of this afternoon in the "innard" of the V4. I disconnected the EY51 heaters no difference. Then the line scan coils at the LOpT. and the line linearity coil ,unfortunatly no difference. I completely took out the LOpT, the line width and linearity coils and gave them a clean, at least I can now see the colours of the cables!, before they looked all sticky black! I did notice that the two gold coloured tubes that enclose the EY51 were metal! The anode side the tube is connected to the EHT overwinding. The other side (cathode) has two wires going into the gold coloured tube but is isolated by a rubber gromit.
So it looks like the LOpT is duff. I am surprised that the fault does not blow the 250mA fuse.

Is the PL81’s G2 feed resistor still ok?

My Pye CTM4 employs a chassis similar to the BREMA IFs version of the VT4.
The line output transformer has been rewound by Mike Barker and I'm now in the process of refitting it.
Link to my CTM4: https://www.vintage-radio.net/forum/...d.php?t=146572

DFWB.

Thanks to everyone for suggestions. It now seems to be LOPT without a doubt.
The set will be going in the loft until I can get hold of a replacement transformer.

Or Ed Dinning to rewind?

I have a set that looks from the front to be the same as your V4. Cabinet fully wormy...
No idea as to its internal condition/LOPT.
Yours (or anybody's!) FOC but I don't think it would courier at all well. A gentle FCS would do it or happy to hang onto it pending collection/meet-up. I may be going to Doncaster in a few months if that's any help.
Graham

Yes please. I will PM you.

Let's see what we can do.
First, though (tomorrow) I need to extract it and check it really is a V4.
Graham