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dominicbeesley · 9th Sep 2011, 11:39 am

Hi Col,

On the CRT earthing question, firstly I'd make sure there is a good earth link between the metal rim of the CRT and the chassis, that seems to be the main earthing point. Then I'd just loop some bare wire or braid from one corner of the metal rim to the other making sure it contacts with the black paint but is well away from all bare area around the HT cap. The contact doesn't have to be great but just touching.

The Metrosil is a Voltage Dependant Resistor which lowers its resistance as the voltage across it increases. The idea behind that is to keep the EHT on the screen roughly constant, otherwise when there is a bright scene the voltage is pulled low and if there is a dark scene it goes high again. This causes "blooming" where bright scenes stretch and go out of focus whereas the darker ones shrink and come back into focus. If you ever watched top of the pops on a rubbish telly in the 70's it looked like someone was fiddling with the camera zoom in time with the disco lights! It will work without this but it is a nice addition and this being a top-notch set it would be good to have all its faculties intact!

I'd double check that the Radio/TV switchover switch is set right and working - it disconnects the heaters of the last few valves and the CRT - you never know....Did you wind up to full mains or leave it at 100V?

Jeffrey is right the lamp will be eating roughly half the mains, so I wouldn't expect it to work well if at all with the lamp in. Either a few in parallel or now you know it's not going to explode it might be time to just run it on the Variac if you're comfortable.

If not I can't see a seperate HT fuse but you could cheat and unplug the HT voltage selector and put the lamp in series with that, this would leave the valve heaters running straight off the mains but would run the "electronics" though the lamp...Personally I'd do a John and give it mains and spot where the smoke comes from!

One thing to watch when running up slowly is the seperate 500mA fuse in line with the Line Output valve - this kept blowing on the last telly I was playing with and after spending ages messing about (and using up my supply of fuses) I realised that it was just that the set didn't like being run at low voltages, I popped in my last fuse and just plugged it straight in and it worked...well the fuse didn't blow!

Dom

9th Sep 2011, 11:39 am	#58
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Restorers dream part 2 the chassis. Hi Col, On the CRT earthing question, firstly I'd make sure there is a good earth link between the metal rim of the CRT and the chassis, that seems to be the main earthing point. Then I'd just loop some bare wire or braid from one corner of the metal rim to the other making sure it contacts with the black paint but is well away from all bare area around the HT cap. The contact doesn't have to be great but just touching. The Metrosil is a Voltage Dependant Resistor which lowers its resistance as the voltage across it increases. The idea behind that is to keep the EHT on the screen roughly constant, otherwise when there is a bright scene the voltage is pulled low and if there is a dark scene it goes high again. This causes "blooming" where bright scenes stretch and go out of focus whereas the darker ones shrink and come back into focus. If you ever watched top of the pops on a rubbish telly in the 70's it looked like someone was fiddling with the camera zoom in time with the disco lights! It will work without this but it is a nice addition and this being a top-notch set it would be good to have all its faculties intact! I'd double check that the Radio/TV switchover switch is set right and working - it disconnects the heaters of the last few valves and the CRT - you never know....Did you wind up to full mains or leave it at 100V? Jeffrey is right the lamp will be eating roughly half the mains, so I wouldn't expect it to work well if at all with the lamp in. Either a few in parallel or now you know it's not going to explode it might be time to just run it on the Variac if you're comfortable. If not I can't see a seperate HT fuse but you could cheat and unplug the HT voltage selector and put the lamp in series with that, this would leave the valve heaters running straight off the mains but would run the "electronics" though the lamp...Personally I'd do a John and give it mains and spot where the smoke comes from! One thing to watch when running up slowly is the seperate 500mA fuse in line with the Line Output valve - this kept blowing on the last telly I was playing with and after spending ages messing about (and using up my supply of fuses) I realised that it was just that the set didn't like being run at low voltages, I popped in my last fuse and just plugged it straight in and it worked...well the fuse didn't blow! Dom