KB QV30/1 width tussles

[AidanLunn]

Hello all,

Some of you who were members of VRAT forums may remember this set and how frustrated at least I was with this damn width problem! After several weeks of confusion, I deduced it must be the LOPT, but still not willing to give up, I will not accept that until I'm absolutely sure!

A background to the width adjustment - the only way of adjusting the width on these models is the width sleeve. There are no width adjusters of any other kind.

There is also not a strong lock on the line hold, but I have checked all components for that between the HT and V6 and everything seems OK there. I have also changed the valve (a PCF80) and still no difference. Adjusting this with no signal input does adjust the width of the raster, but you have to get it up to about 625 line frequency to get the width out fully. The width also seems to come in more on the left side of the raster than the right.

The width problem seems to be on the output stage, possibly after the transformer, as all the voltages in the oscillator and line output valve seem to be correct, as does the boost voltage.

V6 pin 9 is -49V (correct)
V6 pin 1 is 154V (should be 145V)
V7 pin 2 is -49V (should be -44V). C59 has been replaced.
V7 pin 8 is 173V exactly.
The boost HT is 720V (slightly high, should be 710V)
The main HT is 223V, a shade under the 230V the manual says it should be.

I'll own up here and I will say I got rather frustrated with the width sleeve (and I know to be careful with adjusting the width sleeve), so I have put it how the manual described it should be and still not much of a difference. Adjusting it does make a difference to the width but not much.

So, any ideas anyone?

I've attached a picture of the TV and a scan of the relevant part of the circuit.

Many thanks for any assistance and suggestions,
Aidan Lunn

[Peter.N.]

Not an easy one. Have you checked C62 because any reduced capacitance across the LOPT will cause the EHT to rise thus reducing the width.

Peter

[ukcol]

Have you replaced C60 (0.1uF) the capacitor in parallel with L66?

[Heatercathodeshort]

As Peter mentioned, this is a bit of a puzzler. By the look of the picture the EHT looks about right. I would not suspect the LOPT.

Check the 3rd harmonic tuning capacitor. It is C65 on the Newnes circuit [1959/60 page 422] This may have become disconnected, O/C or some one has fitted too low a value in the past.

The line drive may be slightly low. Check the anode load R61 39k also the grid leak 1m R65.

The screen feed resistor to the line output valve is 12K. These are usually around 2.2k-4.7K, worth reducing it's value just to see the effect.

If all else fails increase the value of C65 to around 80-100pf. It needs to be a high voltage ceramic type.

Just a few ideas. John.

The closed loop sleeve between the neck of the CRT and the scan coils is the linearity sleeve not width. What effect does adjusting L51 have?

[AidanLunn]

Hello John, I've just checked and you were looking at the details for the OV30/1, and not the QV30/1, which has a very different circuit. The QV30 is in 1959/60 pages 424-428.

Cheers, Aidan Lunn

[AidanLunn]

Not an update but I should inform users of a slight error in my earlier post -you have to reduce the line oscillator down to about half of 405 frequency to get full width and not increase to about 625 frequency as I previously said. All other information in my OP is correct - checked and double-checked.

Cheers,
Aidan Lunn.

[AidanLunn]

Originally Posted by Peter.N.

Not an easy one. Have you checked C62 because any reduced capacitance across the LOPT will cause the EHT to rise thus reducing the width.

I have ordered some replacements as this set has a 40pF and a 20pF in parallel, which makes me think they have been replaced before.

Originally Posted by ukcol

Have you replaced C60 (0.1uF) the capacitor in parallel with L66?

Yes, with 0.1uF metallised polyester capacitors.

[Heatercathodeshort]

Sorry Aiden! There are so many links and cross references in the KB section of R&TV Servicing, I must have got confused.

Certainly check the 3rd harmonic tuning cap[s]. The value is quite critical. Also check the line oscillator anode load resistor. It may have gone high. The sleeve is used as a width control on the Q30/1 and not a linearity sleeve as is general practise. Not very nice. John.

[The teleman]

Hi Aiden , check c59 line drive coupler.oo3 uf I had a similar fault on a PYE 31 that turned out to be faulty

Chris

[AidanLunn]

Hello Chris.

I've already replaced that.

[AidanLunn]

Well it seems as though the LOP tuning capacitor was about half the value the set needed, although it was 60pF and the manual specifies that. Maybe a mistake in the manual that was followed through on the factory floor or in a service workshop? Maybe a modification introduced after the Trader sheet I have was printed? Maybe a small abnormality in the manufacture of this individual LOPT? Who knows...

I had to put a 100pF "doorknob" ceramic capacitor and a 20pF in parallel to replace the 60pF plus adjust the width sleeve to get the width out. I have also finished off re-capping the set.

As for the weak oscillator, this was indeed down to one of the resistors in the line oscillator's anode circuit going high - R65 had gone high to about 8.8K. Not much higher than the 8.2K in the manual so I didn't think replacing it would make much difference but it has done!

I have also established where this set was destined for. I picked the set up from Brighton from a seller from Southampton who met me there with the set. So I assumed that the set came from Southampton and was tuned to C3 (BBC Rowridge) and C11 (ITA Chillerton Down). But this set was tuned for C3 and C8. The only part of the country which used these VHF frequencies for 405 TV from main transmitters was south-west Wales, C3 from BBC Blaenplwyf and C8 from ITA Preseli. So it's a Welsh TV.

It also came with its original 2-pin round plug. I have taken this off and replaced it with a standard 3-pin but for posterity I have kept the 2-pin.

Now the set is finished and the results are well spectacular! I did have to adjust the brightness down so that my phone camera will take the picture without any bars in the screen.

As I still collected it from the south of England, I thought I'd play a Southern Television startup on it. The continuity announcer's name is Verity Martindill.

Many, many thanks to those who have helped with what at first was a confusing fault! I knew my perseverance with the set would pay off, even if it was put to one side for many months!

[Hunts smoothing bomb]

A nice looking set with a nice picture.
Spot on advice from John too, right on the money as usual.

Cheers

[Freya]

Glad you sorted in the end, I know its been bugging you for ages.

[Peter.N.]

I have had to change the value of that capacitor to put sets right for no apparent reason, pleased you found it.

Peter

[AidanLunn]

It seems all is not over...

As soon as I had finished the set, I re-examined the tuner and I found that the Channel 5, Channel 8 and Channel 4 tuner biscuits were in the wrong positions and wrong order! This led me to think it was on Channel 8 when actually the set was receiving something from Channel 5 - confirmed by fitting a splitter to the Aurora output and feeding the same signal into both the KB and my Ultra V14-53 - the Ultra (which I know to be a good, reliable set) had the Aurora output on C5 whereas the KB had it on what the knob on the front said was C8. This was when I discovered the tuner biscuits were the wrong way round.

So I swapped them over.

"So what's the problem?" I hear you all ask. I'll tell you.

It turns out that this set is not a Preseli/Blaenplwyf (C8/C3) set - the tuner biscuit confusion above is the reason for me originally coming to that now incorrect conclusion before I discovered some were in the wrong positions. The set still has its original retailer sticker on the back from 1959/1960 - a Southampton based company. So the set *is* after all a Rowridge and Chillerton Down set.

The fault is that when I tuned the set to Channel 3 (Rowridge's frequency), it worked fine. Tuned to channel 11 (Chillerton Down) and poor HF response with no sound. I tried all band 1 channels and they were all fine. All band three channels either do not work properly (if at all) or have poor HF response/no sound. By this point my patience with the set was running on empty so I decided to (carefully) put the set back in its cabinet for now while I turn my attention to my Pye CTM17T "Continental", reasoning that the KB still worked fine on Band 1 channels. After I put it in its cabinet, there was sound on vision on channels 2-5 now, only channel 1 was working OK. This is most likely down to the speaker wire not being positioned correctly, as it has to pass fairly close to the IF coils before it reaches the speaker plug on the main chassis...

So before I come back to this I have my Pye CTM17T ad my Ekco TMB272 to finish off - the Pye has developed a top frame linearity fault that is really irritating and my Ekco needs a few bits finishing off (dry joint on aerial socket, EHT smoothing not working as well as it should after I replaced the Visc with a homebrew ceramic-in-a-film tub affair and... tuner problems).

The Ekco TMB272 is why I'm delaying this KB until after the Ekco, as the Ekco also has tuner alignment problems (*any* channel you put in it will only appear on C5 - C1? Only appears on C5 biscuit. C10? Only appears on C5 biscuit etc) and I've never done a full tuner alignment before so I thought I'd practice on the Ekco before doing one on the KB.

Incidentally, I will tune the KB in for C11 as that is what it would have originally run on for ITV, but as most of my other sets run on C9, C9 is my standard channel, so the set's C9 biscuit will also be tuned in (it is present) and utilised.

So... what tools would I need for a tuner biscuit alignment? I know I must make sure both valves are in tip-top form and these will be my first check but this is why I am a pessimist for a reason. I've seen this before on other sets and changing the valves made little difference on those...

Meanwhile all that said, here are pictures of the set working on C1. The "Queen" is beautiful, isn't she?