Hi all,

Recently, I am mucking around with some Tektronix scopes and other equipment with CRT's. To date, I only play with the PSU's and low voltage amplifiers and other circuitry.

I am comfortable around 500/600v in my old radios, but in this type of equipment, there are Test points around 3 to 4kV, and higher accelerating voltages of 10 to 12kV.

Not wanting to "fry" myself accidentally, I am seeking some advice as to how you work with HV circuits safely. Eg. How do you discharge the HV anode? Do you also discharge the PSU caps before working on a TV? What equipment/tools do you use? etc etc etc..

I am aware that one has to be ultra careful .... and it would be ultra dumb not to draw on your experience.

I don't work on TV's but do occasionally work on RF linear amplifiers which have very high voltage on the output valves.

Before poking around in such devices I use a "chicken stick" to bleed off any residual voltage.

I made my own, but they are available for purchase:

https://www.stewmac.com/luthier-tools-and-supplies/tools-by-job/tools-for-electronics/amplifier-tools/snufferstick-high-voltage-discharge-stick/

Hi GTC,

"chicken stick" .... ... an appropriate name .... "fried chicken" ????

Chicken Stick is an American term. I guess it's childishly derogatory in the sense that users are not being moronically "brave".

Hi GTC,,
Agree 100% ... moronically brave is very apt description ....

Hi GTC et al,

I have purchased a Fluke HV probe and had some 'tuition' on HV for the Scopes I am working on ... so I'm more comfortable around HV now.

I do intend to make a couple of SnifferSticks ... one being a straight short to Ground, and one with a resistor in the probe. Using the 3 of them in sequence, or as appropriate, should reduce the chances of "frying" myself ....

Very early TVs had mains-derived EHT that was definitely lethal. No 2nd chances with those things, they could jump out, bite you and fry you.

The biggest danger from newer designs is the HT that's about the same as a valve radio. The EHT, even though it's in the order of 20 kV, has a high effective series resistance. It can give you a nasty fright, cause you to swear loudly and drop something like a CRT. The resulting implosion is more dangerous.

Be aware that some oscilloscopes with CRT's have negative voltages into the thousands.
A HV probe which is plugged into a meter will be fine but a stand alone HV probe will not.

Hi Irext,

This is an area where I want t be absolutely clear that I am safe ... so, to be certain that I understand your point here ... Is the distinguishing safety feature between the types of Probes (safe and unsafe), a Ground lead??

My HV probe plugs into a DMM (battery operated, not Mains operated), and has a Ground lead. One must ensure that this is connected to a known Mains Ground Earth connection, which is connected to Ground, not to a piece of equipment which is sitting on the Bench unplugged .... eg. I connect the HV Probe Ground lead to the scope under test which has the Chassis grounded.

As distinct from ... a HV probe with a Meter incorporated in the Probe, without any Ground lead????

A HV probe which is connected to a DVM will be fine as the meter is capable of measuring negative voltages.

A stand alone HV probe is only capable of measuring positive voltages.

The story goes that a tech was killed measuring negative high voltage on a microwave oven using a stand alone probe.

He connected the ground lead of the probe to the magnetron negative HV supply and the tip of the probe to ground.

The probe arced from the centre of the voltmeter on the probe to his hand and as the HV supply in the microwave could supply several hundred watts he was killed instantly.

Your DVM connected probe should be fine.