Having to work around the HV and live chassis question

[DavGoodlin]

Hi Jon, Thanks for putting safety first
-Take a long, flat-blade screwdriver and attach an alligator clip jumper cable between the shaft, near the handle and ground it to the HV cage or spring/metal part on the CRT mounting. Then slide the flat blade between the CRT and HV (fat wire, often red) where it attaches to the CRT's ultor button, it may be open or under a rubber cap. You will hear a snap if there was stored potential.

If the set powers up but does not operate, the power supply filter capacitors could hold a charge also. Ground a clip lead to the capacitor can and touch to any large power resistors off the cap and that should do it.

I have been zapped by 25,000 volts (color GE-KD) once by pulling the HV regulator 6BK4 tube cap, after switching the set off. I was just not being careful a few times 35 or so years back. I do not recommend it unless you like having the jitters the rest of the day.

Dave G

[ketron281989]

Originally Posted by DavGoodlin

Hi Jon, Thanks for putting safety first
-Take a long, flat-blade screwdriver and attach an alligator clip jumper cable between the shaft, near the handle and ground it to the HV cage or spring/metal part on the CRT mounting. Then slide the flat blade between the CRT and HV (fat wire, often red) where it attaches to the CRT's ultor button, it may be open or under a rubber cap. You will hear a snap if there was stored potential.

If the set powers up but does not operate, the power supply filter capacitors could hold a charge also. Ground a clip lead to the capacitor can and touch to any large power resistors off the cap and that should do it.

I have been zapped by 25,000 volts (color GE-KD) once by pulling the HV regulator 6BK4 tube cap, after switching the set off. I was just not being careful a few times 35 or so years back. I do not recommend it unless you like having the jitters the rest of the day.

Dave G

Hi Dave, thanks for your response, this sounds easy to rig up but is there a possiblity to perhaps show a picture, sorry I dont mean to be difficult. I just want to make sure I make it correctly. Thanks

Jon

[Penthode]

Be especially careful with sets that do not use a power transformer. The power line is connected to the chassis and if the power plug is inserted into the outlet the wrong way, the chassis will be at 120VAC with respect to ground.

And beware of the metal cone CRT. It runs at a very high voltage ((12000 to over 20,000 volts). While the current behind this voltage is not lethal, the zap will send you flying into the next two or three adjacent rooms.

Seriously, I worked in a TV repair shop in the late 60's and the owner told me his first encounter some twenty years earlier with an RCA set with a metal cone CRT. He reached in to change a tube while the set was on and the impulse reaction from contact with the metal bell and the resultant belt caused him to jerk his arm and badly slice it on the metalwork. He showed me the bad scar on his arm. The vivid memory of his story has yielded a healthy respect I have for the voltage, which has prevented me from ever receiving a shock from the metal tube.

Apart from the 120VAC, the B plus supply (300 volts or more) requires the most respect.

[marty59]

When you're working with a live set, always remember the "one hand rule".

You keep one hand behind you while the other is probing/testing etc. so you don't make a complete circuit across your body. Rubber soled shoes are a good idea on concrete/damp floors too.

[old_coot88]

Remember that a CRT can partially 'recover' after being discharged. So it's a good idea to discharge it a second and third or more times, waiting several minutes between each hit. Or just leave the jumper in place for a while.

[ketron281989]

Ok thanks for the help guys, needless to say I am still scared of course. Any extra input would really help as knowledge on this subject could save my life or from some nasty stuff occurring with the voltages.

Thank you

Jon

[marty59]

Originally Posted by ketron281989

Ok thanks for the help guys, needless to say I am still scared of course. Any extra input would really help as knowledge on this subject could save my life or from some nasty stuff occurring with the voltages.

Thank you

Jon

The "buddy system" also applies until you're more confidant. It's understandable to be skiddish and it's good to put safety first!