High voltage in TV

[Zener_Diode]

Hey
How can I messure the high voltage in TV? I don't have special messure devices, I thought to build a voltage divider, but according to the calculations I need a resestor 10Mom 40Waat to messure 20KV, with 1000V mesurement device. I don't know if such a resestor exist and if it is, it will be very expansive.
Does some one has an idea how can I messure a high voltage, without spending much many???

thanks ahead.

 

[Nigel Goodwin]

You use a high voltage probe, these used to be fairly commonly available, and plugged in to the standard AVO 8 multi-meter. The AVO 8 was (and still is) an analogue multi-meter with a specification of 20,000 ohms/volt, so on the 1000V range had a resistance of 20,000,000 ohms. The probe was a simple series resistor - a VERY large one, in a thick plastic handle, with a probe at one end and a lead at the other that plugged in to the Avo. For a 30KV range the resistor needed to be 29 times the resistance of the meter, 580,000,000 ohms.

At FSD it would draw 50uA from the EHT, as the meter did on all ranges, notice that a digtal meter with it's 10Mohm resistance on all ranges would take 100uA on it's 1000V range!.

So for a 30KV range on a 1000V digital meter you require a series resistance of 290Mohms - bearing in mind the voltage ratings that resistors can handle!. Perhaps 29x10Mohm resistors in series?.

 

[Zener_Diode]

ok, thanks.
Do you know the maximum high voltage that can be in TV?

 

[HiTech]

All depends upon the size of the crt and circuit design. Typically the max voltage is around 26-30kv. Avg. values are more like 20-24kv. Why do you need to measure this parameter? Unless you probe the crt anode properly, you risk arcing to ground and damaging the Horiz output section or at the least, shocking yourself a good one. Over the last decade, I may have measured HV value only a few times... if that when serviving a tv set. The HV value is the least of my concerns.

 

[Zener_Diode]

one of the problems that can be is unfocused picture or black screen.
in both problems there are 7-30KV.

 

[Nigel Goodwin]

The usual voltage quoted for colour TV's is 25KV - very large sets may be a bit higher, and small sets a bit less - but 25KV is a good average value.

It's very rare to need to measure it, usually it's either there or it's not, I probably use my high voltage meter (an old Eagle HV probe/meter) for measuring the focus voltage more than the EHT.

Bear in mind the picture size is directly related to the EHT voltage - the lower the voltage the larger the picture (slower electrons take less power to deflect).

 

[HiTech]

**broken link removed**

This is very similar to mine; includes a handy meter to measure up to 40kv. Cost me $5 at a used equipment sale.