Hi guys, college has been keeping away from my hobby but I will finally have time to take care of some cosmetic and cleaning issues. I told you all about my Philco 50T-1402, well this applies to any TV I would be working with, my question:

When I am working with a live set, or need to pull out a chassis from a set that has been used within the last week or two, what do I not touch?

I am guessing the HV tubes? The HV cage? The HV cord that goes to the CRT?

I would hate to end my life from one of these sets or get a jolt, thanks for the answers guys this is a important question I have been thinking about for some time.

Jon

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 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

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.

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.

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.

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

I've seen a recommendation for having a resistor in line between the shorting screwdriver and ground. Thoughts?

I've seen a recommendation for having a resistor in line between the shorting screwdriver and ground. Thoughts?

I've seen that recommendation too. I made me a grounding probe using a resistor but most times I just use just a test lead to a screwdriver.

Carl

I've seen a recommendation for having a resistor in line between the shorting screwdriver and ground. Thoughts?

I'd believe this applies more with discharging electrolytics.

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!

A couple things:

If that set uses the chassis I think of, it has a glass CRT and a standard power transformer power supply (not a hot chassis). The CRT can't store enough power to be fatal (unless you have health/heart problems), but it can knock you away and give you a nasty injury from that.

With that said, the rules of safety are to do as those above said, and discharge the CRT by connecting a plastic handled screwdriver to the chassis with a clip lead, and poke it under the rubber cap on the high voltage wire (the fat wire to the bell of the CRT; not on the socket). That will ground out anything in the tube. There is a faint possibility that the electrolytic cans could store a shock, but that too can't really do any damage other than embarrassment if someone is watching, LOL. It's also a general rule to keep your non-dominant hand securely in your pocket when you're doing anything on a powered circuit. That way, the theory is that the current will bypass your heart in case of a bad shock, and not enter one hand and exit the other (right across the heart), if your other hand happens to hit ground, which it might if it's just dangling or leaning on the table.

The way I got into this hobby when I was 9 or 10 years old, is I got hold of a book for the amateur; "Professional TV Repair Secrets" by Art Margolis. He wrote a lot of consumer-level booklets on TV repair, and most any of those would be a great source for the basics of not hurting yourself or the valuable TV. Try eBay or Amazon for those. Art's books are mostly from the 50s and 60s, and include all the tips on late 40s and early 50s TVs.

NOTE: There are a few Philco TVs from the late 40s and early 50s, and a DuMont from '46, which have a DEADLY danger. They have a "direct step-up" power supply, which has an oil-filled capacitor in the power supply which is capable of a fatal shock. Yours isn't one of those, as far as I remember, but generally you need to watch out for oil-filled capacitors in power supplies, as they can be a few uF at up to 10,000 volts.

Charles

Here are some photos where I discharged the HV on my Zenith 25HC50 chassis set. These run the highest 2nd anode voltage I am aware of.:yikes:

old coot88 - added that this voltage can partially recover, so once is not enough. So true!
Also, beware of kines that barely light up because those will store even more kV! Don't be fooled by a dim CRT.

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