UK Vintage Radio Repair and Restoration Discussion Forum - PYE LV20/B18T 1948. Heart transplant.

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PYE LV20/B18T 1948. Heart transplant.

I found this very dilapidated PYE LV20 in the loft of a large storage shed at the rear of a very long established radio shop in Hanworth Middlesex. The shed had all the appearances of a 1930's scout hut and was crammed with old, partly dismantled receivers including the remains of a number of pre war television receivers. Interesting as the area must have been partly DC mains by the number of DC only receivers that were stored in another part of the shed.

The owner who I believe had passed away in his late 90's was a Cossor dealer and by the look of some of the paperwork discovered, had sold a fair number of pre war television receivers.This was a few decades ago when collecting old receivers did not have the interest it does today.

I managed to find some useful valves and a few semi complete receivers, the LV20 being one of them. At the time I thought it might be of use as spares, having a few of the B18T series in my growing collection back at the shop.
It was stored away in the huge shed at the back of the old shop [It covered the entire what had been a garden] and followed me to my present home, hiding out of sight on the floor at the rear of my 'museum'.

Recently to make better use of the space available I have been parting with mostly run of the mill broadcast receivers. There is nothing of interest for me on AM radio these days and to be honest that goes for FM as well. Time to have a sort out and keep a good representative range and chuck out the junk! This is how this tatty LV20 came to light.

As I dragged it into view the top of the backless cabinet came adrift. The glue had dried out and it simply fell apart. The only advantage is that it is now easy to give the EF50 valves a wiggle without having to delve inside and cop a belt off the EHT..

I'm not going to go into all the details of the repair as this has been well covered in the past. Replacements involving an EF50 valve, loads of decoupling sticky slugs, wax insulated capacitors, well out of tolerance resistors, small electrolytics, slider presets, loads of time but of course all good fun.

If you really want to know all the horror you only have to be cruel to me and ask..Just a note to say that it is well worth taking the time to clean the EF50 pins and spigot. I use a small rotary brass brush powered by a mini drill. They are all now trouble free and can be tapped and rocked in their holders without disturbance. The sockets can be cleaned with a tiny spot of good quality switch cleaner, just a spot to each 'hole'.

The B18T was released in September 1948 and was Britain's first 'transformerless' television. When I say transformerless I mean it did not have a mains transformer for heaters, HT and EHT. It sported flyback EHT and the first television receiver to employ a series heater chain. It would also operate on DC mains providing the supply was not less than 230V but this was not actually intended at the time. It was the PYE agents on DC mains that brought this to PYE's attention.

As I mentioned the EHT was derived from the line flyback and it may have been the first British receiver to do so. It was soon followed about a year later by the Bush TV11 and the Ferguson 941T. It is possible that the KB CV40 may have beaten it to the post but this was a very rare model unlike the Pye that was produced in many tens of thousands.

Back in 1948 the early line output transformers employed in the B18T/LV20 were the height of technology and were operating at the cliff edge. They were very reliable in service and I remember carting home quite a few 9" treasures from jumble sales as a lad and all the transformers were fully functional.

Six decades on unfortunately the insulation is failing as it was on this chassis. The whole assembly is potted in pitch making a rewind a very difficult and messy job. The EHT overwind is constructed in small wave wound sections each very close together and it must be the most difficult task to take on.

Your a brave guy Mike!

As I have a couple of B18T's in working order I decided to have a play with this one and see if I could get a much simpler transformer from my junk box to operate reasonably.[I really must get out more often] It is a fairly simple line output circuit with a PL38 line output valve feeding the primary of the LOPT together with it's multiple section EHT overwind. The isolated secondary feeds the scanning coils with a small well insulated winding supplying the 6.3V required for the EY51 EHT rectifier. A PY31 acting as an early efficiency diode completes the picture.

Removing the original transformer in it's black screening cover is an epic in itself. The smoothing choke has to be removed to gain access to the fixing screws and at first sight the connecting wires vanish into the chassis wiring. It must have been a difficult task to wire up on the assembly line and I take my hat off to the ladies that did it! I wonder how many chassis worked first time on first test?

Extension leads were fitted with crocodile clips to make transformer substitution an easy matter. A number of transformers were tried ranging from an Ekco T161 through to a motley collection of mostly unknowns. Most gave some results with either severe lack of width, low EHT or a combination of the two.

I then struck lucky with a neat transformer manufactured by Allan components. I suspect it had been designed for one of the many home construction kits of the early 50's. It had very similar resistance readings to the original and suitable for low resistance line scanning coils. It had a decent EY51 fitted so I was in with a chance.

It was soon connected up and gave splendid results. I did not wire in the width inductor that was originally wired in series with the scan coils. The EHT measured 6.5KV and what could be seen of the diabolical raster, was of sufficient width.

It was time to get the chassis into shape as mentioned earlier and after a lot of frustrating work managed to get a very good result on the 70 year old PYE. It is exactly the same age as me but I'm not sure who is in the better condition.

It was an interesting project, the sort of thing my school mate Clive and myself would have done way back in 1960. We used frame output transformers for audio output and the reverse, even finding a few that made good heater transformers. All manner of make do and mend to get pictures on those jumble sale delights. We played about with all manner of odd transformers and components the results of which usually ended up in clouds of stinking smoke and a telling off from our poor frustrated parents.

I'm going to tidy it up and fit the replacement transformer in place of the original. There is just about enough space for it fortunately. The line linearity is not perfect, probably due to a miss match between the scanning coils and the transformer or a similar miss match on the primary. I was not aiming for perfection with this chassis, just a reasonable picture. It is only a project.

The pictures show the progress and the end result. I must say the 9" screen is very watchable and does not detract from the entertainment factor.

Way back in 1948 It must have provided enormous pleasure for the family of it's original purchaser. By the look of the chassis, they obtained many hours of pioneer entertainment from their first television receiver.
I hope you enjoyed my excursion back to my school days in 1960. Seems only 10 years ago.
Regards, John.