PYE B16T 9" table model 1946.

[Heatercathodeshort]

PYE B16T 9" table model 1946
This PYE B16T was presented to the museum a couple of weeks ago. From what I understand it had remained in the same family since purchased new and had ended it's days as a display piece in a TV showroom.

Recently I have been tackling with my joint curator of the television dept, several interesting receivers, the recent PYE being one of them.

Before we go any further I would like to say a word of warning. These early post war models derived their 6KV EHT from a mains transformer, high voltage rectifier [HVR2] and a .1uf 7KV smoothing capacitor. A very great danger exists if you come into contact with any of the high voltage terminations and that is very easy with the B16T due to the top cap of the HVR2 and the positive terminal of the smoothing capacitor being very much within reach. I have fitted a BULGIN insulated top cap connector to the HVR2 and a short length of plastic pipe over the capacitor connections. The two 27M resistors wired across the EHT supply were O/C creating another very dangerous situation. I switched off and after 30 mins discharged the .1uf to earth. There was quite a meaty flash just waiting for someone to grab hold of it. With the 27M resistors replaced by a chain of 10M, the capacitor was fully discharged in five seconds.

YOU HAVE BEEN WARNED!

The heavy chassis was easily removed. Both control knobs were curled up bits of plastic. This receiver is an early user of plastics and I have come across PYE control knobs in a similar condition on PYE broadcast receivers of a similar vintage. Strange because the decomposition appears to happen regardless of storage conditions, many survive unscathed. I have a few decent PYE knobs in the boxes in the spooky garage loft so it's not a problem.

On first examination the PYE appeared to be very clean and original. Just a thin layer of dust with no signs of any work being carried out. A close examination of the chassis however revealed that the original MW22-7 CRT [This may have first appeared in 1939?] had been replaced by it's official replacement the MW22-14C on the 18th October 1949 the date stamped on the warning label.

The MW22-7 are excellent tubes, I believe produced in the PHILIPS factory at Eindhoven, fitted almost exclusively to post was receivers with mains derived EHT. I can only guess that the tube may have had a mild flash over and with the current available from the EHT supply may have either blown open circuit an electrode connection or blasted the cathode. It is interesting to note that PYE fitted a surge limiting resistor to the input of the HVR2 in later production.

Tipping the heavy chassis on it's side and blocking with 6" stubs of 2X4, a closer examination revealed nothing amiss. The frame blocking oscillator transformer looked quite new compared with the rest of the components and with it's correct part number stamped on the top must have been an official part supplied by the PYE spares dept.

A few checks were made for HT shorts and it was noted that the .1uf EHT smoothing capacitor was the very reliable circular Aluminium can style DUBILIAR with the brown Bakelite insulator on the top. If it had been the TCC Visconol it would have been linked out of circuit no matter how loudly it protested. [Believe me they do protest!] A fellow Forum member discovered one of these in a B16T and to his horror, while he was working on it the brown bomber exploded sending shards of Bakelite, paper and oil all over the room! I hope he was wearing a nappy.. With flyback EHT it simply collapses due to the high impedance low current source but with a mains derived arrangement the power just keeps coming heating the thing up till it pops!

Feeling confident that death was at least a few years away I did what I always do and plug it in. All the valves lit and after a short time had elapsed a very faint wickerwork/partial frame collapse/ lack of width raster if you could call it that, appeared on the tube face. At least the EHT transformer was OK and the tube would produce a picture. Connecting an aerial to the original flying lead produced nothing even with the vision sensitivity and contrast to maximum. With an ear close to the loudspeaker there was a complete absence of sound not even a trace of hum. Thoughts of an O/C primary on the output transformer flashed into view but that's just my pessimistic view having experienced many year of television servicing.

The first to tackle was the HT supply, electrolytics, wire wound supply resistors and other routine checks. A quick meter check confirmed that one of a pair HT distribution wire wound 1k resistors was O/C. A circuit check revealed that this fed the sound output stage and a meter check across the audio o/pTx resulted in slight pops from the speaker confirming it's innocence.

At this stage It was decided to replace the main electrolytics very conveniently mounted on a bracket at the bottom of the chassis together with the 1.5k w/w.

Upon removal they were all well down on capacity and a couple had the usual chicken poo seeping from their base seals. The three were neatly replaced and the UU8 rectifier visually checked to see if it had been under stress. I do not test rectifiers on my AVO characteristic tester for fear of blowing up the brand new meter I recently fitted. It's just not worth it. Rectifiers usually blow up, develop O/C heaters or produce reduced emission and you don't need a tester to tell you that! The UU8 appeared to be innocent of any visible destructive qualities. They are very good at covering up their guilt as discovered when I unpacked two brand new UU8s and fitted them in turn to an Ekco TS46. Both produced a shower of sparks and blown fuses. After exhaustive checks it turned out they were simply having a hissy fit. A third one produced 100% results. It is often the rattling old second hand ones that work fine, a bit like the Mullard PZ30 and the U801.

The original rectifier in early versions of the 16T was a Mullard GX32 with a 5V heater. later versions employed the Mazda UU8 requiring a change of base to Mazda Octal and a modified mains transformer to accommodate the 4V heater of the rather dated UU8. No doubt certain valves were difficult to supply in quantity during the austere post war period especially rectifiers.

Powering up produced a better result. With the brightness control fully advanced the scrambled screen mess was a bit brighter, the electromagnetic focus could be sharply set in the center of the focus pot and there was the usual low level hum from the speaker.

Next to tackle was the brightness control circuitry. The tube is cathode modulated with the brightness control simply connected via a potential divider across the H.T rail. The decoupler to the top end of the control [.1uf] read around 100K and was quickly snipped out of circuit. Up flashed a brilliant [search light!] scramble with the brightness control now working correctly.

Next the frame timebase. I won't bore you with this as we have done it many times before. This utilizes a big fat double triode the Mullard ECC34. One half is the frame blocking oscillator with an extra winding on the transformer to allow for injection of the frame synchronizing pulses, the other being the output stage. All very simple and straightforward.

All the usual tired troops were now to be retired from duty including the usual waxies and the incontinent bias electrolytic.
20Powering up again produced a much better result and after smearing the wire wound sliders with MS4 silicon grease easily managed to obtain a steady raster. It was lacking in width and the line linearity was a bit off but hey! It was waking up!

We now needed a signal to see what was happening. Application of full blast from my RF system produced nothing, not even a peep of sound. The PYE 41.5/45mc/s TRF strip is a very well constructed unit. How those ladies on the production line produced such magic in such quantities never fails to amaze me. The RF interstage coils are tiny, enclosed in copper cans. EF50 valves are employed as they were in similar Radar receiver strips during WW2. These excellent valves were originally introduced in 1939 and were very welcomed by the industry capable as they were of dealing with 50mc/s signals with ease compared with the large B7 based types such as the TSP4 and the Mazda AC/SP3. Mazda were producing the well known SP41[4v] and later the SP61[6v] but it had a very greedy heater current, a top cap and was fitted on that lossy Mazda Octal base. The EF50 was a revelation with it's direct glass button base.

Saying that the EF50 did have a few problems mainly due to quality control and inconsistency but considering they were made in many countries, they did a good job. I think the American versions, Sylvania/RCA etc were the best quality and were often marked up as Mullard valves with the best quality ones used in sensitive positions. These were marked with two black lines on the top. The pins also suffered from tarnishing and could have been a tiny bit longer to make better contact with the holder itself. The holders were of mixed quality. The Paxolin type were nasty but the ceramic types are much improved but of course more costly. Various types of securing rings and springs were employed to keep them in place.

Removing the screening plate from the receiver unit was a mixed experience. Nothing had been disturbed but I was presented with a sea of tiny .001uf 400v wax decoupling capacitors. Upon assembly these had obviously been laid in a special sequence as they were tucked in everywhere and there exhumation was not going to be easy..

It was a labour of love. First was to deal with the black valve pins. These were carefully cleaned, including the spigot that locates the valve and earths it's Aluminium can, finishing with a tiny spot of MS4 grease on each pin. There are as many as five caps per valve each clutch soldered to a common earthing point. I used micro pliars and a selection of sharp 'pickers' to deal with each stage. A test after dealing with the first common RF stage produced an encouraging weak signal. It was a very tedious job replacing these capacitors attempting to keep them in the same position as the originals. Failure to do this can result in miss alignment and instability.

With all the caps replaced, strong audio and video signals were at last coming through and it was necessary to reduce the signal input considerably. With some adjustment a locked picture could be obtained with good contrast and brightness but a bit smeary.

Two electrolytics required replacement C10A 16uf the video amps HT supply anode decoupler cleaned up the picture. At the same time the C11A 2uf connected in parallel with R13A 47k the video feed to the tube cathode was replaced. It is mainly present to reduce aircraft flutter. It was completely O/C reducing the tube drive. The same network was used in the later PYE B18T and most other makers receivers, with varying component values.

Replacement of these two caps made a dramatic improvement in picture quality producing a very high brightness [thanks to the mains EHT] stable and high contrast picture.

The results were good but not up to the standard there receivers are capable of.

The next to examine was the line output stage. The picture was lacking about an inch either side with poor linearity. The line output valve is the familiar Mullard EL38 in a typical class A configuration. It is not required to generate flyback EHT resulting in the line output transformer being very similar to an audio output transformer. The difference being of course it is designed to operate efficiently at 10kc/s and enjoys very good insulation.

The transformer is enclosed in a Aluminium can with a Bakelite top that contains the line linearity correction/damping components namely R45A 2k 6W C30A .007uf 700v and the wire wound adjuster slider R46A 1k 6W. You guessed it. Operating the slider massively increased the picture width at one end then decreased it abruptly mid way. It was O/C. The resistive element was replaced with some considerable difficulty by removing the guts of a Radiospares 11 watt ceramic wire wound resistor and fitting it into the Bakelite top with adjustment to the slider contacts. It now works correctly and presented a correctly presented line scan.

From cold switch on the width took longer to fill the screen that it should have done. The EL38 was the original fat version with internal glass sprayed grey/blue. A replacement soon sorted that out and a full picture appeared after a the normal warm up.

The EHT rectifier HVR2 is designed to heat slowly allowing the timebase valves to come to operating temperature before the EHT. The Mazda U22 has similar cathode characteristics but does not have anything approaching the life of an HVR2!

The finished result is outstanding. The vision and sound gain presets are set a third advanced together with the contrast control. Definition is incredible complete with plenty of good quality sound. [EL33] output. A few valves were replaced due to microphonic effects and the HVR2 glowed a bit odd. All the usual valve holder cleaning and tickling of course was carried out.

These were ground breaking receivers that soon gained a reputation for reliability and capable of receiving a good signal from distant transmitters. I believe they were first released in early 1946. The ERT states the table model B16T was released in May 1946 and the console model in July. I had a customer, a very grand and influential lady that purchased her D16T console and had it installed the day before the Victory Parade in London. [June 6th ?] I have that very receiver in good working order together with the PYE V14C she purchased 10 years later! It must be one of the very early models.

It's surprising how many of these have survived. The cabinet was bone dry and faded. Some Beeswax thinned with White Spirit has given it a better appearance and I'm going to retain the original finish. The cabinet back is like new complete with it's original PYE retaining screws.

Pictures show :1 Internal. 2 Chassis on bench. 3 Lethal EHT power unit before fitting protectors. 4 Another internal shot. 5 UU8 rectifier and ECC34 valves.

[This PYE D16T can be seen at the museum when conditions permit.]
John and Peter. Curators, TV Dept. Dulwich museum.

[Heatercathodeshort]

The remaining pictures. My camera does not like bright high contrast tv pictures and tends to highlight bright areas. They do not do justice to the live picture. Regards, John and Peter.

[dragonser]

Hi,
what a good write up and bright picture as a result of the repairs....
thank you both.

[Heatercathodeshort]

Correction. The valve behind the UU8 is of course the EL33 sound output valve not the ECC34 frame osc/output...
Thanks Peter B. It did take most of the morning LOL!

[Boulevardier]

Thanks both for an exhaustive and fascinating write-up. Those unmistakeable EF50s always bring memories flooding back...

Mike

[peter_scott]

Another great result after quite a mammoth repair. I don't envy you having to deal with all those 0.001uF decouplers. Thanks for posting. I must look out for those two bars on my EF50s.

Peter

[Heatercathodeshort]

Hello moderators. Could you please change the title to B16T! I always get these numbers mixed. Thank you. John.

[newlite4]

Always had rather a soft spot for the D18T having seen one in the Science Museum in around 1974. I had just reached the stage of preservation as opposed to rendering for spares and felt what a nice compact set they were. Growing up in Bath meant that most old TVs dated from 1959 onwards so the really early ones as seen in the London area were hard to track down. Lovely write up John, nice to see the internal details, truly an historical instrument.
Neil

[Heatercathodeshort]

Yes you must Peter.
You will get an extra shilling for the ones with the stripes! They advertised them like that in the back of the Practical television. You will often find the striped Mullard branded ones in the first RF stage and frame output stages in Pye receivers.

Picture shows 1&3 Mullard [Made in USA striped]. 2 Plain can VR91 probably GEC or Cossor. 4 Mullard UK 5 Osram Z90 and 6 NOS Mullard UK

I suspect there were many more valve manufacturers working together with this vital component.

[murphyv310]

Hi.
Us mere mortals never land up with a set with a "Light layer of dust"
I've done both a B16T and a D16T in the last 10 months and they were really a mess. What with corroded EF50 valve bases and significant rust both sets were resurrected and are now displaying good pictures. One MW22-7 was completely shot but did able to get improvement with the slow reactivation process. The other the CRT was down to air. My good friend Frank sent me one and the result was indeed very good.
They are awkward to work on and the first one had slider control issues.
Not a bad set but I think I've had my fill of them, perhaps if I was fortunate to have a light layer of dust set I'd feel better.

Even late last year I got a Bush TV24C for £15 off ebay, boy was it grotty and I really thought it was a scrapper with no valves and the CRT base disconnected. Well after my famous washing process a recap, valves and a few other little repairs, it's brilliant and I defy anyone that there is a better one around, its just stunning. Another mess of a set, so filthy that it would make you ill only needed 1 electrolytic and a rectifier and again it's perfect mind you it's a Russian Rekord 14 inch from 1957, far superior components to ours still original caps and resistors all spot on, the cap and HT rectifier were missing and that's it, amazing.

[Heatercathodeshort]

Well Trevor you will keep dredging junk out of Kilmarnock Water. You will never find a 'thin layer of dust' on that sort of kit.
Oh well your Bush came up well so it must be down to the clean Scottish water. Regards, John.

[eddie_ce]

John, thanks for a brilliant write-up. Really enjoyed reading it. I always shudder thinking about mains derived EHT.
When I am able to visit the green and pleasant land again, I look forward to another visit to the museum.
Re the EF50, you probably know there is a great article on the interweb, if my memory serves me correctly its titled "EF50 the valve that won the war". For those who haven't read it, it's highly recommended.
I hope I haven't hi-jacked your thread with that information.

[Heatercathodeshort]

I forgot to mention that I added a 60m/a 1 1/4" fuse in a plastic holder from the hot end of the EHT winding to the HVR2 anode. Don't use a 20mm one. The gap when blown is small enough to create an arc over. The mains transformer is the complete transformer supplying EHT, HT and valve heaters. It is very robust and must have been a very expensive component to manufacture. No doubt war time production experience helped to a manufacture a reliable transformer at reasonable cost. Most mains EHT transformers of the period broke down in service.

Recently a few have broken down due to the peak voltage across the rectifier, all of 12kv punching through the heater winding insulation destroying the transformer. Mike Barker can engineer a very good rewind that no doubt will out live it's owner. [Other guys rewinding transformers are available]

The 60 m/a fuse will protect the transformer should a fault develop in the EHT smoothing capacitor or if the EHT rectifier decides to commit suicide.

I'm always a bit nervous when I post a receiver that has mains derived EHT. You really have to great care when working on chassis of this type. Make sure the chassis is rigid on the bench backed up with wood blocks. make up six or so, you will find them very handy when working on record autochangers etc. A scrap length of 2X4 cut into 6" lengths or so will make service work easier and at the very least may prevent damage to the equipment being serviced and in the case of mains derived EHT systems, your life!
You must prevent the chassis from falling on yourself trapping your hands or arms. Keep all pets, children well away from your work area. Take your time checking everything and if your not sure what you are doing, switch off at the very least and get some advice from this Forum.

Sorry if this sounds a bit Nanny but knowledge is better than ignorance. Take great care. Regards, John

PS Thanks for the info Eddie. I have not seen the EF50 story. I write everything from memory! J.

[FERNSEH]

Pye employed the EF50 valve in the pre-war models 9C and 12C. The chassis was designated 915. Very early EF50s had hooked pins. These were quickly replaced by the short straight pins we are familiar with now.

DFWB.

[beery]

Hi John,
That's a really nice example. The console version is quite common, but the table model you have here is much rarer. The art deco speaker grill is a nice touch
Yes those 1nF RF decouplers are annoying. The little bits of fabric insulation tape on the edges of the screening covers is a bit of an afterthought.
As with all PYE sets, the picture linearity is spot on.

I once restored a console version at Gerry's many years ago.
I have an Invicta T102 which used left over D16 parts. The big mains transformer was dispensed with, being replaced with a series heater chain for most of the valves and a voltage doubler for the ht. EHT was provided by a second line frequency transformer, without an efficiency diode. The set could not run on DC though because a small heater transformer was required for rhe CRT and voltage doubling HT rectifier. A very strange set.

Back to the set in question. I'm currently reading "Radio Man, the rise and fall of C. O. Stanley". It covers, as others here have mentioned, the development of the prewar 915 chassis. It points out that C. O. had Mullard (through Philips, Eindhoven) develop the EF50 specifically for the PYE 915.
It also states that the reason that D16 was so advanced and available for sale just before TV was relaunched in 1946, was because PYE had illegally been transmitting their own 405 line signals to test the receiver design before Ally Pally came back on the air. You wouldn't get away with that today.

So all in all a fascinating set and a good restoration write up.

Cheers
Andy

[Heatercathodeshort]

The Invicta T102 is certainly an odd mix of D16T parts! It really is odd. "To my knowledge they never produced a PYE branded version of this. 2 X PL38s if I remember correctly I discovered this example in a huge dry shed/building at the rear of a radio & television shop that had originally, in the 1920's been a cycle shop. Quite a number of pre war TV receivers had been sold from this establishment, mainly Cossor. It's a very interesting story and maybe when I tow that T102 [seen in the picture on the shelf] into shore I will tell you about it. It's knobs appeared to be missing but were later discovered inside the cabinet in a paper bag wrapped in a bit of newspaper dated 1960. I repaired it many years ago but not a full waxie change, so I suspect it may need some attention.

Back to the B/D16T. I have two console versions both with interesting stories. The first one I mentioned earlier, was owned by the grand old lady riddled with cats! One of them ripped the speaker cloth and the results can just about be seen in the picture. All part of it's history. It was repaired many years ago and has held up quite well.

The second one together with a number of other receivers was obtained from another elderly customer. Her late husband had been very interested in television and used to visit jumble sales in the early 60's. He had passed away many years ago leaving around five receivers to collect dust in that upper room.

I discovered a little hard backed note book where he had listed the models he had obtained with 'broken up' against the ones he had scrapped. These included HMV 904s, 1804s and a couple of 1807s. I know....but they were just junk back then.

The D16T together with a number of other receivers were stored in the upper room of a massive Edwardian house in a 'nice' part of Surrey.

All the TV receivers were in immaculate condition having been stored since retirement in a warm dry atmosphere. All of them had that 'thin layer of dust' feeling. It was a time warp.

History over. With the D16T on the workbench back at my old shop, I simply repaired it. The .1uf 7kv cap [it was a Visconol] was useless together with a few age related faults. It can just about be seen in one of the pictures. I will get it out when I can raise the mental state and see how it's aged. A recap will be required..

Pictures show The Invicta T102. The first D16T. [cats] Screen shot from same. The last one is the 2nd one obtained from the elderly lady. It is somewhat buried at the moment protected with carpet tiles and cardboard. I MUST get it out!

[peter_scott]

John, It's great to hear the details of where your sets came from.

Peter

[Edward Huggins]

Gosh, all this brings back memories. In those days the loudspeaker diameter almost matched that of the CRT. And they did sound good too....but that was not to last for long.

[Heatercathodeshort]

When viewing a small picture particularly the 9" models I find it adds enormously to the entertainment value to have first class sound. I have comfortably watched many films on small receivers, even good musicals and don't feel I am 'missing out' but the sound has to be well above average.

Some console models actually had speakers bigger than the screen Edward! J.
.