Earth Leakage Clamp Meter - Great Tool!

Most TVs prior to the introduction of SCART sockets had a mains derived power that made the chassis live or neutral;  or if it was a Phillips, then live on negative half cycles, and neutral on the positive cycles, as the rectifier was a bridge.


In all cases that  I recall the antenna isolation was 1000 pf or so of capacitance twice, being in the centre and another one in the braid of the coax. Problem is the set would keep working perfectly even if the capacitor had failed, but would then be very 'tingly' indeed, saw that at least a couple of times. These were the sets where pulling the plastic volume know off revealed a live brass shaft, and in one design I cannot remember the make,  under some unfortunate condition the metal speaker grill could become live, and there was a stock fix to over sleeve the speaker wires.


There were audio transformers with mains thickness insulation for headphones in the 1970s, but I do not recall seeing an RF transformer antenna isolation until after the SCART era, by which time the PSU was fully isolating and a generally more standardized approach was being adopted and  CE marking and safety tests followed a bit later.

I recall the antenna isolation was 1000 pf or so of capacitance twice,

That makes sense. I'm sure I found at least one with an actual transformer on the aerial socket - it was like a short co-ax extension lead with a very over-sized socket assembly that slotted into the compressed cardboard back cover. Thinking about it it possibly wasn't UHF - given these would have been old sets even in my youth perhaps more likely a 405-line VHF set (or there was at least one dual standard one). Luckily my parents didn't really understand the hazards of letting an 11-year old play with the EHT section of mains powered set with the back off....


   - Andy.

Those Cathode Ray Tubes could give a real kick

Oh yes - the glass was metallised on the inside and the outside to form the EHT smoothing capacitor, and the EHT went in via a large press-stud on the side - due to a problem the CRT kathodes went cold before the EHT o the anode ran down, then the tube remained a fully charged capacitor with the voltage accessible to the careless thumb if you were changing a defective tube.

I recall getting a shock to my hand and dropping one, luckily flat on the face, so it survived with no implosion. Still a very sharp intake of breath moment. Plenty of black and white dual standard sets sold from mid 60s  up to the early  70s, as for quite a while not all the channels were available on UHF in all areas of the UK. As old bangers a few of these were still going ten years later, and some crossed my path as repair projects. Pre printed circuit TV repair was something else, to keep cost down as many  components as could be just  strung between the valve  holders,   a bit like this, but grubbier   and simple paxolin tag solder strips  this stuff  where they could not. By modern standards very poor thermal management, so when they got full of fluff a fire was not unknown.

There were even a few dual-standard colour sets.


We had a Phillips G6 (bought as an ex-rental from a place in Chepstow), lots of nice glowing things in the back which ran with the cover off to let out the nearly 1kW of heat. Great for keeping the frost off the poor newlyweds in the winter (a truly dual-purpose appliance, you can't watch the match on a fan heater).


A regular fix for these things was to solder up the 1-zillion way slider switch which changed 405/625 so it stayed 625 and was a lot more reliable.


These things didn't have EHT triplers, the flyback overwind went straight to 25kV at more mA than I wanted to get near!

I love my CRT tellies - the picture is so much better. ?