KB 17" mains transportable PVP20 1958

[Heatercathodeshort]

KB 17" TRANSPORTABLE PVP20 1958
They say that all that glitters is not gold. Likewise most items that are considered to have a 'cult' status turn out to be the worst examples of their art..

Take this KB PVP20 17" mains transportable. Produced at the start of the contemporary period 1958-1963 probably inspired by the Sputnik and space travel mania that was present at that time. Granny would not have approved.

This example was presented to me a long time ago and has been stored suitably wrapped until a few weeks ago. To gain access to the guts you have to remove the case shell. It is made of compressed cardboard, quite a quality item when you compare it to similar constructed cabinets of this period. To do this the receiver is placed face down on a soft cloth. The handle, four pink plastic feet, channel selector, volume brightness and fine tuning knobs have to be removed. Next are the two plastic side panels that surround a bank of six presets on the left and the channel selector, fine tuner, brightness and volume controls on the right. Once you have removed all the plastic bits the cabinet should slide off giving access to the chassis.

The first sight was not a pleasant one. The LOPT together with it's matt black screening cover were missing. No problem I though because I had a NOS LOPT marked 'Royal Star' on the outside. My excitement soon cooled when upon examination it was in fact the transformer fitted in the 110 degree later version known as the QVP30. This is a much nicer model with an autotransformer for the heater supply dumping the heat producing mains dropper in the earlier PVP20. More of this to follow. The chassis was a bit scruffy but dusty and dry.

Not a lot could be done about this other than to fit an alternative transformer but with this crazy KB it was a labour of love too far!

Two weeks ago I had a phone call from a fellow vintage enthusiast that asked me if I could identify three boxes of LOPTs, scan coils and other treasures. We ploughed through them and would you believe it there was a used PVP20 transformer amongst them! It had sustained slight damage breaking away the EHT output connection but that could easily be repaired. A quick test on my LOPT tester showed it to be intact with no shorts so I was in with a chance. Transformer testers must always be viewed with caution. They are, as is most test equipment a guide. A useful guide but with no guarantees. The transformer was kindly gifted to me [thanks John] and it was time to pull that pink horror to bits and have another go.

This time a more detailed examination was made of the chassis. All the disgusting TCC 'Platiseal' capacitors had been replaced in the 1960's and a neat job was made of it. Access is terrible with two printed panels mounted on an oval steel plate. These can be loosened after releasing their fixing screws but short leads soldered to back of the panel prevent any serious movement. To add to the horror the mains dropper has to be released and placed on it's side in an attempt to unsolder any of the components on the timebase panel. The IF panel has no rear access. Nasty for KB!

The chassis other than it's nasty service access is very similar to the RV10 CROWN. Originally it was fitted with a BRIMAR 17" electrostatically focused 90 degree CRT type C17SM but at some time in it's life had been replaced with a Mullard AW43-80. The mains voltage selector was set for 240/250V always a good sign. Three valves were missing types PY800, ECC83 and PCF80. The tuner is the reliable 'FIREBALL' but a sloppy repair guy had omitted to replace the screening cans when he replaced the PCC84 and PCF80 valves. [That drives me potty!] Other than that the chassis looked quite tidy giving me encouragement to repair the damaged LOPT.

It was quite an easy job. The EHT overwind was not steeped in tar just finished with the usual tar tyre. This was just warmed with the heat gun making it very easy to peel it off in large pieces. The output wire was soon located and one turn removed to allow easy connection of a new lead out wire, top cap cover and clip. A sort length of the very thin wire was then wound around a more robust wire and the end soldered. Cut tape was then placed over the winding allowing the wire to be held in place. Resin was then painted over the whole overwind insulating it and strengthening the new connection to the R19 EHT rectifier.

With the transformer fitted and mains applied I was rewarded with a very acceptable picture. OK a bit out of shape with all the controls needing a squirt of cleaner but due to those Plastiseal capacitors having been replaced by the lovely Mullard mustards there was little to do capacitor wise. A few of those low value HUNTS were still in circuit, you know the ones I call 'cockroaches' that crunch up when you try to remove them. They were a pain to replace!

After a short period of operation the width started to reduce... Oh no! The dreaded saturation but I was wrong. A temperature test of the overwind proved it was very cool and a new PL36 line output valve soon put an end to that crisis. The width control plug is now on 'MIN' giving plenty of width with 16KV EHT.

The height control was fully advanced to fill the screen. The 1.8M resistor feeding the anode of the frame oscillator was reading 2.8M. It's replacement reset the height pot to midway.

It was noticed that the picture was slightly grainy even with a strong signal, in fact it was very similar with an 18DB attenuator connected to the aerial input. A replacement PCC84 and PCF80 valves made no improvement but it was noticed that for a fraction of a second, when changing channels the gain shot up. Clearly the AGC circuit was holding the gain down especially the voltage applied to the PCC84 RF amplifier.

This turned out to be an O/C 10M resistor associated with the contrast control back off supply to the AGC line of the RF stage. A full strength picture returned giving very high contrast and a surprisingly good picture, it's very watchable. The same cannot be said about the sound. A tiny 4" speaker on the top of the chassis is all you get. The cone was rubbing on the magnet giving that classic grating sound at low volume levels. Years of muck was blown out with the gentle use of my air line and a liberal coating of diluted 'W' adhesive stiffened up the very soft cone. Care was taken not to get any of the adhesive onto the loudspeaker suspension. The distortion is no more.

CONCLUSION

The PVP20 is quite a clever design born just before the swinging 60's with it's Teak Scandinavian look. The problem is the trendy designers don't understand the shortcomings of a poorly ventilated chassis, the KB being a typical example. There are two small grills at the bottom of the cabinet and a small single one at the top. Add to this the mains dropper and line output stage and you had a recipe for trouble. The TCC Plastiseal capacitors were susceptible to leakage even with a well ventilated chassis. When I was first in the trade I well remember them leaking badly and they were less than four years old.. After a half hours use and the heat built up the frame would creep up an alarming amount and this was a similar problem with the Sobell TPS series transportables. Replacing these caps in the TPS resulted in one of the most reliable receivers of it's time. We have a Sobell TPS173 at the museum. It will run for hours on end without a flicker! Considering it's extraordinary design it is surprising that so many PVP20s were sold. Only a year before everything was brown Walnut.

The cabinet has stood the test of time. It is constructed of heavy grade compressed cardboard painted a dark stippled silver. There is also a version finished in bright red! The first time I encountered one I thought someone had self sprayed it red. They are very rare. Inside the case their is a company stamp of it's maker, G.R. Robinson of Byfleet Surrey. The PVP weighs a ton! I doubt if many were actually moved around the house. Being relatively small in size they tended to be installed in restricted areas such as wide bookshelves and open fronted cupboards adding to the heat problem. I have left all the 60's repairs in place. It is all part of it's history so don't blame me for the scruffy appearance! To be honest it's not easy to keep this chassis tidy not helped by the lack of the EHT screening and tuner valve screens.

All I can say is it works and I would think it's original owner was delighted with his space age TV. The pictures speak for themselves.

As mentioned earlier, in 1960 KB produced a much tidier version of the Royal Star, the QVP30. It has an almost identical appearance to the earlier model but was much slimmer employing the short neck Brimar 110 degree tube. These models were much rarer than the PVP20 and were very reliable. Gone was the mains dropper replaced by an auto transformer [shades of the Bush DAC90] resulting in much cooler operation. A final version was released in 1961 that was basically the QVP with circuit modifications.
End of story!
Regards, John.

[Heatercathodeshort]

Some pictures off screen. The camera effects spoil the good interlace plus the patterning. The scan coils were difficult to move due to the slide screws being seized. I have now been able to straighten the picture. J.

[toshiba tony]

I remember these, just. Did they have an oil filled lopty, things are a bit vague or perhaps I'm thinking of a totally different set, thanks.

[Heatercathodeshort]

Hello Tony,
The KB never employed oil filled transformers. I was thinking of the Murphy V230 and V350 models but they had 'open' transformers. I guess they thought the risk of an oil leak in a transportable may have caused problems. Yes it was a very long time ago. John.

[agardiner]

Great job. And the tube at least looks great. Nice one.

[Panrock]

Good write-up from John as usual. One of these was my very first set, delivered to our door when I was about 15, in exchange for a ten bob note. It worked, too...

Steve

[Hybrid tellies]

Brilliant job and great write up John. That tube looks nice and bright.
Interesting that they used a PCB board for the IF when they switched back to a completely hand wired chassis for the VC1 dual standard chassis.

[Restoration73]

Nice one John, I saw that set on the side at the workshop. They make some very small DC
fans that might fit to assist the ventilation.

It is clear to see the design is a precursor to the later VC11 Featherlight d/s chassis.

[thermionic]

Lovely job again John, you make it look too easy!

I have one of these in my pile that I must get to one day. You appear to be lucky in that the plastic trim on the bottom of the screen is intact. I’ve seen many of these models over the years where this piece ( at least ) is damaged or missing. My quest continues.........

I like to imagine that this chassis was designed by ‘ the new boy’. A fresh engineer not long out of short trousers brought in to give KB a space age set. PCB’S......What? You can almost see the old seasoned engineers shaking their heads slowly whilst sucking on their pipes.

......but I guess they got their way, as they soon went back to hand wired chassis!

Cheers. SimonT.

[Panrock]

A problem on mine was the rear foot, which broke through the cabinet material. I attempted to fit a strengthening plate.

On this set I watched the 1966 World Cup in the garden, using a 5ft telescopic aerial attached to the set as a quarter-wave whip.

This set was also smuggled into my boarding school.

Steve

[Heatercathodeshort]

Ha! Ha! Mine has three feet screwed very secure into the base of the chassis itself. This may have been a later modification due to the dreaded foot collapse. I used to fix it with penny washers! Maybe it was the 110 degree version that had only three feet? It was always the rear one that did the disappearing act. John.

[beery]

Hi John,
As ever a great restoration and write up.
My first ever 405 line set was given to me by my Physics teacher. However I purchased my second set (an Invicta T102B with pealing veneer) from an antique shop in Leigh-on-Sea. Anyway, at the same time they tried to get me to purchase a KB Royal Star, I think it was the 110 degree version you mentioned. Anyway, it had a broken handle, so with that and it being far too kitch for me, I steered well clear of it. That would have been on the late 80s or early 90s. I've often wondered what they were like to work on (I'm not curious enough to buy one though).

Cheers
Andy

[Heatercathodeshort]

Great comments! Thanks. Ref my post 11. I should have said my PVP20 has FOUR feet and it is the 110 degree version that has three with the collapse of the single rear foot! J.

[Tazman1966]

Thanks for the interesting write up as always and just what I need to jolt me back into action. It's been too long away from my workshop, to be honest.

[Sideband]

Excellent results John. I have one of these with a duff CRT. Can I have the one out of yours?

Agree with accessibility problems. I have special memories of one of these.....right back to the very start of my servicing career before I started at Philips. I was working for a small TV repair shop and one of these came in for just a routine repair....changing caps in the field output stage. Then it started to fail with different things every few months or so, the last repair was a shorted overwind which we pinched off a scrapper to get this one going cheaply. The chief engineer was curious as to why it was so unreliable and it looked like the set was leading a hard life so while giving me a lift home one afternoon, we dropped the set off at the customers house. The TV was installed in the back room and was working fine. While chatting to the customer we were offered some tea while she put some washing away. Before we left, the engineer went into the back room to check the set and nearly fainted.....! Draped over the back of the set was the washing that the customer had been folding earlier. Apparently she did this all the time as it 'got nice and warm behind the TV.....'!

No wonder it had been unreliable....The engineer had a few harsh words with her while I sat in the van and waited. he never told me what he said to her and just muttered about stupid customers all the way home.....but we never saw the set again!

[peter_scott]

Thanks for another excellent write-up John. I particularly liked the AGC problem.

Peter

[Heatercathodeshort]

Originally Posted by Sideband

Excellent results John. I have one of these with a duff CRT. Can I have the one out of yours?

The original tube is a Brimar C17SM. It can be replaced by the much more familiar Mullard AW43-80 or the Mazda CME1702 with no circuit changes but the Mazda was only used in a few receivers, and then only for a short time before the 110 degree CME1703 tube was unveiled. John.

[Heatercathodeshort]

Just a memory from the past. After leaving school I continued to work at D&B Television until I was 18, then I went solo. The people involved are unlikely to still be with us as they were quite elderly back then, or at least they were to an 17 year old.

I was asked by a close neighbour to D&B to have a look at their Royal Star. They had a long established construction business and lived close by with a yard at the rear. The horrible Pink thing was lurking in the back parlour of the premises standing on one of those old built in cupboards with a curtain across the bottom. It was very cramped probably getting very hot and was suffering from leaky Plastiseals..

I collected the RS, replaced the caps, cleaned the Fireball tuner and to be honest it was quite a good picture. After a long soak test I returned the RS the next day and spent a while tidying the aerial and mains leads. The customer was very happy with the picture and was about to pay me just about enough to buy a packet of Marrowfat Peas when there was a sudden KAPLUNK! The rear foot had collapsed into the cabinet leaving the screen pointing upwards like a WW2 searchlight.

Unplug everything and return to workshop to reinforce said foot with 'Penny washers'. There was no fibreglass back then generally available to the public, pity as that would have made a very satisfactory repair.

With the implant complete all was happy and I got paid. She was a charming Welch lady with a delightful Welch accent. It was a long time ago but never forgotten! John