GEC BT448 Early Version.

[MickMcmichael]

“Sign here mate” said the courier as he stood on my doorstep one day last summer.

“Got a pen?” I asked, innocently.

“Use yer finger, it’s digical” came the reply.

I signed his dimwitwidget digital device which advises the whole world that I’ve just bought something, dragged the box into the lounge and noticed that “her indoors” was wearing her Jeremy Paxman face. She was poised with twenty questions. She doesn’t have to write them down anymore; she knows them off by heart!

“Not another ruddy record player?”

“No!”

“Job lot of radio’s?”

“No!”

“Some pile of dusty old kak?”

“Probably”

What had actually arrived was this wonderful old GEC BT448 television from around 1962. It’s the early version of this model which uses a 30PL14 in the frame output and a 30P19 in the line output stages. No UHF tuner but it has a 405/625 switch on the customer control panel.

It was advertised with £7.95 postage. An offer I couldn’t refuse!

So off came all of the “FRAGILE” red and white tape from the box which was made up from several different thicknesses of cardboard. Various packing materials were sent flying, thrown and strewn over the carpet as I unpacked the box, like a dog digging for a lost bone!

“I hope you’re going to clear that up!”

“Yes dear...”

The set came out of the box apparently undamaged. It was carefully carried to the workshop for an initial inspection of all gubbins.

A snow-capped 30PL14 lay in the bottom of the cabinet. The line timebase board was somewhat skew-wiff due to a previous repairer not fixing it back into the chassis with the four 4BA screws in each corner of the board. No other damage evident other than a couple of pieces of wood from inside the cabinet. These were only back cover location guides. It looked like the tube had survived the journey from Wales to Peterborough (as indeed was later proved) so a sigh of relief was breathed and the set was put into service hibernation – until time allowed a closer look.

January 2019 came quickly and it was time to do a telly. I couldn’t decide which one to do so her indoors suggested ( somewhat sarcastically ) that I service the first set that I trip over in 2019.

Cue the GEC....!

I carefully lifted the set onto the bench whilst nursing a bruised left forearm and upper thigh. A decision was made to just plug it in without reforming the smoother first. This decision was based on pain, laziness and an inability to find my capacitor reforming device, buried under mountains of stuff. Set plugged into mains and switch on.

A “tinkle” could be heard from the chassis... a sound which told me the heaters were open circuit and would not warm up the workshop until the break had been found.

I located a provisional service sheet from a pile of manuals I had been meaning to sort out and followed the heater chain across the service sheet. In at pin 5 and out pin 4 etc, etc. Out of IF board and into the tuner to V1 and V2. Out of tuner and back to IF board to PCL84 (sound) and then the CRT, V18.

A break was found in the print on the IF board. Heaters now alight but very low EHT and no raster. These days I always judge how much EHT I’ve got by the amount of disturbance I can muster on my workshop freeview box by touching the line output top caps with a big screwdriver! In past times, EHT was judged by a spark long enough to light a cigarette. Her indoors put paid to that.

There were many old Hunts capacitors around all stages of the set. These had to be changed before a diagnosis could be confirmed. I’m not one to change components for the sake of it but there were so many of them, especially in the boost and S correction stages. They had to be replaced.

Time for tea. Change the caps tomorrow after I’ve nursed my injuries with some foul smelling deep heat gel and a glass of whisky.

Updates to follow in due course.

Happy new year to all.

Regards,

Mick.

[slidertogrid]

That's an unusual set Mick, I have never seen one before. I have a couple of the bow front sets (405 only) and four of the later dual standard sets.
This looks like an interim model, probably not made for long?
Full of nasty cracked Hunts ? It looks in good cosmetic condition. I will follow it's restoration with great interest!


Rich.

[Nickthedentist]

What a brilliant story, LL-J lives again

[FERNSEH]

An earlier discussion about the GEC BT448:
https://www.vintage-radio.net/forum/...ad.php?t=90600

DFWB.

[Hybrid tellies]

I rescued one of these from the local TV shop scrap heap when I was about 15. When I got it home I was quite surprised when I switched it on and it worked. It was the slightly later version with a valved UHF 625 line tuner. I managed to keep it going for a few years before I swapped it in for a newer set.
The main problem was getting the UHF tuner to work on the high end of the UHF band where the Mendip transmitter channels were located. After a few months BBC2 would start to fade out followed by ITV then BBC1 which would always mean a replacement PC86 or trying to adjust the poor contacts on the valve base.