Watch your fingers and face when doing that. Picture tubes have a few 'nasties' inside them with the main one being lead, a heavy metal that can cause a few problems when handled the wrong way.

Lead can be found in the glass. It was added to strengthen it in order to handle the negative air pressure inside and to stop people putting their feet through the front when their footy side was dealt a blow. The lead also absorbs the x-rays emitted by the tube during normal operation.

Many picture tubes are fitted with a phosphor coating that contains cadmium which can lead to blood poisoning if it comes into contact with cuts and abrasions or mucus membranes (lips, eyes, etc). In a general sense, if you any of several types of phosphors on a wound it will not heal correctly either.

Now I have a bit better knowledge of what I'm dealing with, after a little zap from the anode. I was servicing a THOMSON Telecontrol TS-3652 (1970's or 80's colour), but it didn't occur to me that there may not be a bleeder resistor. Oh well, I'm still here, and I'm not missing any limbs.

Any idea of what the anode voltage for a 14" set like this would be? What's the standard anode voltage for a 13.5" set? I know my 5" tubes have 8kv behind the anode... A nice little shock there.

Chris

A while ago I read on http://lowendmac.com/tech/crt_danger.html that the charge retained in a CRT is very high voltage, but not a high quantum of charge - ie the farad scale - and therefore low current. So it can deliver a memorable momentary shock or an impressive spark, but is not inherently dangerous to a healthy human body.

The secondary danger is real, however, as the shock can be harmful or even fatal if the shockee has some pre-existing heart condition or incurs physical injury from the muscular reaction to the shock. This can include heart attacks, or strokes brought on as a result of a single heart spasm.

I still make it my business to avoid those shocks!

Maven

Agreed. Best to avoid. When I got zapped by my picture tube it still clamped my chest for a brief moment. I've been zapped by the mains a few times too. Neither type of shock is pleasant by any means. Keep in mind that 50mA can kill a healthy male. Women, children and senior citizens can succumb to a lesser shock.

This is why RCDs are set for 30mA in domestic and commercial installations and 10mA in the cardiac-protected areas of hospitals.

About 40 KV dc should be enough. Earth to a connection on the 'tensioned Earth wire'. These wires Earth the coating on the back of the tube. They then go to the chassis earth. The implosion protection is inside the tube.
I just tap one of the pins back inside the tube. Usually one tap and you can hear the air entering the tube. Do you wear the required face shield while working on tubes? If one implodes it will be one of the loudest sounds you have ever heard and glass will go everywhere at high speed.
I think it is called 'O'tooles law'.

ps. I didn't see page no. 2

Between 4 and 28 KV I think, depending on size.
The recycle center told me the mercury in the tube is the main reason that televisions cannot be put into burried waste.
If you discharge a tube and leave it a few minutes, a charge will return, although not as great as before.

I don't know what it is about CRTs, but they seem to be temperamental buggers. I've discharged many television sets (still using a screwdriver!), even only a few minutes after being turned off, with no spectacular effects. However, yesterday, I discharged a 34cm Philips about 5-10mins after being turned off (maybe even longer), and heard a loud 'pop' as the anode grounded through my screwdriver to the external coating on the tube (graphite aquadag).

Boy, that made me jump! After so long, I've gotten used to there being no audible or visual effect when grounding a tube! Even larger 27" tubes never resulted in anything spectacular.

The joys of 'ancient' television repair eh?

Chris