Thank you - be sure to check out and use the "video index" file, linked on the channel homepage (lower right corner of the banner graphic).

It's encouraging to me to see young people getting into electronics. Good luck to you!

famos and Alan. Be very careful when using HV Probes for measuring Ham Amplifier Plate Supplies. If you check the paper work for most HV Probes they will tell you they are rated for CAT 3 or CAT 2 work. These are very low energy applications as in a CRT Anode --- 10 KV @ 5 ma or less. While the voltage for an SB-220 plate supply is considerably less -- 3 KV -- it is capable of delivering upward of 1 Amp at that voltage. If something were to breakdown, either in your probe or your meter, at that energy level things will get very nasty very quick ! As in an explosion. I'm not saying that will necessarily happen but be prepared for that to happen. Safety Glasses are essential and electrician's gloves are a good idea. The Fluke 87 III & 87 V are rated CAT 4 to 600 Volts and CAT 3 to 1000 Volts. Using a High Voltage Probe throws all of that out the window. Even though 1/100th of the measured voltage is dropped across the meter input if the probe ground connection fails or the meter input circuitry fails every volt that you are measuring gets transferred to the meter. In that circumstance the probe resistor is all that stands between you and disaster. Be extra careful. You don't get second chances at these voltages. Bob K6TR

Excellent comments Bob, and right on the money! Thanks for your valuable contribution.

carefull with measuring amps, I made the mistake of taking the probe off when the amp was in use(TX) and created a nice arc (untill the fuse blew)

***** Another good point. One must use extreme caution with High energy linear amps. Very lethal.

Essential comments Bob. While I used to poke at TV anodes with 20+ kV, I much prefer to set up an amplifier HV metering test with isolated gear and then observe, not touch, when power is turned on.

i realize it's quite off topic but do anybody know of a good place to watch new movies online?

@Robert Valentino I would suggest flixzone. You can find it by googling :)

@Kevin Noe yup, have been using flixzone for since march myself :D

@Kevin Noe Thanks, I went there and it seems like a nice service :D Appreciate it!!

@Robert Valentino no problem :)

The TV tech that I worked with during my first job (in High School) at a TV repair shop called it the 2nd anode, so that's what I've called it ever since...

Second anode it is. It's connected to the conductive aquadag that coats the inside of the bell of the CRT. After the electrons strike the inside of the phosphor-coated glass screen, they must be removed from the CRT. This is how they escape. The aquadag is also connected to the "accelerator grid" of the electron gun, giving the electrons their final, attractive positive potential, speeding them toward the front of the CRT.

***** I appreciate this is a trivial matter but being called the 'Final Anode' makes sense as it is the Last thing in the tube before the phosphor front, but 2nd Anode, Final Anode, what the heck.... but if I may comment on the function of this anode.: It's not there to 'remove' the Electrons, it is there to give the final impetus for the Electrons to hit the screen with enough energy to excite the Phosphor coating. If you lower the Line O/P Voltage (adjusting the EHT or Final/2nd Anode Voltage) the Electrons will slow down and the deflection coils will have a greater effect as the Electrons are in their field for longer, this will make the resultant picture on the tube front larger and dimmer, the reverse will happen if you increase the EHT, producing a smaller but brighter picture.

That's a common misconception. Here is what is REALLY happening: The EHT potential is the same at both the aquadag coating the inside of the bell of the CRT and the "accelerator grid" which is the ring of metal at the "front" (the end closest to the screen of the CRT) of the electron gun assembly. The kinetic energy of the electrons speeds them toward the front of the screen, having been propelled by the potential difference between the cathodes of the electron gun assembly and the “screen grid” (G2), followed by focusing and, finally, the accelerator grid. The electrons are not “pulled” toward the screen by the potential at the second anode. They are “shot” from the electron gun. Yes, the same EHT does the trick but it's the EHT at the accelerator grid that provides the impetus. Remember that there is NO POTENTIAL DIFFERENCE between the accelerator grid and the aquadag. It's all at EHT potential. Inertia keeps the electrons traveling in a straight line after they leave the electron gun. It takes the extremely powerful magnetic fields from the deflection yoke to push and pull this beam around, as you know. Electrostatic fields won't do the trick unless the deflection plates are extremely close to the electron beam (as in an oscilloscope CRT). The electrostatic field from the EHT charged aquadag has no effect on the electron beam at this point. After the electrons strike the phosphor-coated inside of the CRT screen, they have traded all of their kinetic energy for light and a tiny bit of heat. The “spent” electrons bounce off the insulating glass of the CRT but they must not be allowed to remain inside the bell of the CRT. If they do, they will form a negatively charged cloud in the bell of the CRT. It is this cloud that causes the “blooming” symptom you describe where the image expands on all sides as the negatively charged electron “beam” is now repelled by the negatively charged cloud that's floating in the middle of the CRT. The expanded image is not caused by the electrons slowing down and creating a greater angle of deflection as they pass more slowly through the magnetic field of the yoke. They are sort of dodging the repulsive electron cloud that's in the bell of the CRT. You can clearly see this in extreme cases of “low EHT” (which sounds oxymoronic when you say it) where the middle of the screen goes dim or dark as the electrons are not hitting it with enough force. If this were simply a deflection angle issue, the image would still be evenly illuminated, just overscanned. Enter EHT at the Second Anode to the rescue! Since these “spent” electrons no longer posses kinetic energy, they are now pretty easy to grab and suck them out. They're just sort of floating around in there. After striking the front of the CRT screen, the negatively charged electrons are then attracted to the positively charged aquadag that lines the bell of the CRT. They are conducted along the aquadag, out the second anode connection and into the EHT unit (flyback) and, eventually, passed to ground.

***** Boy I thought I could write long replies lol What you say sounds good but I was only reciting from my college days from 1981-3. My memory may have failed a tad maybe. Can I ask you this? You say the expansion of the picture is due to the Electrons being repelled by the negative charge cloud, if so why isn't the middle of the expanded picture completely or unevenly distorted? I was shown the result of low EHT in class and the picture was normal but larger and dimmer. I have trouble with accepting the flyback of the line o/p signal to the line o/p transformer has anything to do with attracting electrons, Feeding this signal through a few voltage doubler circuits involving Diodes and Capacitors, the flyback part of the signal has little effect due to these components and the next sweep signal simply adds to the voltage thus giving the 'doubling' effect. This seems sound to me but am willing to be shown otherwise. I learned my Electronics during these college years but haven't dealt with a CRT TV since then and by the looks of it, never will, I'm glad to say.

No, these probes are intended for DC or very low frequency measurements with a meter. There are special HV oscilloscope probes available from various manufacturers for that purpose.

High voltage probe design for high frequency measurements is not trivial. I am not aware of simple low cost solutions.

Thanks Alan. I figured there wouldn't be a simple solution. I was thinking of some method that didn't involve direct measurement. Asking doesn't hurt though. :) Thanks for your quick response. All the best... Jim

I'm certain that the probes and instrumentation used for high voltage utility work today is much safer and more robust. Probes like the ones shown in this video are intended only for low energy/capacity applications, not high power apps like that.

I'm not quite sure, but my guess would be mid-60s to mid-70s.

I think you're right,the guy of who i bought,said me exactly the same thing.

Sorry for my poor english.

That is correct if you use the "low-medium-high voltage" nomenclature commonly used in power systems and generation-distribution. For example I work in digital electronics, anything below 3.3v is low voltage and over 12v is high voltage. So it depends on the context. For instrumentation, anything over 1kV is high voltage.

The probe shown in the video is rated to 50,000V max. It is no longer manufactured by RCA. Fluke makes one that is rated to 40kV: www.fluke.com/en-us/product/accessories/probes/fluke-80k-40 Cal-Test also has a 40kV probe. They're pricey - $100-$300 or so. Here is a probe rated for 100kV: www.cpshv.com/products/500.htm Measurements of such extremely high voltage typically requires specialized equipment such as: vitrek.com/4700-precision-high-voltage-meter/

That's what I am working on at this time. What is the wattage rating of the resistors and pot that you used?

+jpmvidal High Voltage probes are designed to be connected to a particular impedance or a particular type of instrument. A 10MHz HV probe is most likely intended for connection to an oscilloscope with a 1Mohm input impedance, so it may not read properly on a DMM. You would have to consult the probe's datasheet to be sure.

+Raja Gama Suhadanto If the probe does not state that it is suitable for AC measurements, then I would not use it. High voltage is not something you want to take chances with.

+w2aew thanks for youre respons

I'll add this to my list of videos "to do".

***** Thanx, that would be more than great!

It depends on the particular probe. It will have the maximum rating on the label of the probe.

ik it has been 6 years but how did you embed your link into a blue text? very curious about it. =)

@@ChamasGemeasAndrePetya Magic using what youtube wanted.

+bones007able The DMM can measure negative voltage - so the connections remain the same.

I have a analog meter

+bones007able You'd have to swap the leads, but you must be very careful - this may put the metal parts of the meter at dangerous voltages. It may not be designed for that.

so if I earth ground the clip , should give some protection ?, it has internal 10meg resistance, most DMM I find locally harbor freight , menards etc... do not list any internal resistance , if they do they are no where near 10 megs...

+bones007able HV probes like the one I showed MUST be used with a meter with 10M input impedance. WIth other HV probes, your mileage may vary. CAUTION: Measuring such high voltage with equipment that wasn't specifically designed/rated for it, even if using a HV probe, can be lethal. Don't do it.

The resistor in that probe (the one with the meter) is an 800Mohm resistor, which is too high to be read with a Fluke 289 (maximum reading of 500Mohm), so it will show as OL even if the resistor is good. You'll need a different meter to measure that resistor. The meter movement can be tested separately (see my video on D'Arsonval meter movements). For what it's worth, here is the manual for the HV probe with the meter: lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Heathkit%2040%20KV%20Probe%20Meter%20Model%20IM-5210.pdf

I must admit that I did not know my meter well enough, but I was thinking about the limitations of it, when I wrote this message - sorry about that. But, how would I know if the resistor is working or not? When I measure the meter itself, I can see the arm moving a little, so I was thinking that the resistor isn't in working order. Also, there are 2 similar resistors in the front part of the probe, but the bottom one (closest to the tip) is a different color, it is darker brown - is that normal? Is that is how your probe looks to you? Or they are identical in color? Thank you for the manual of your probe, mine doesn't have a SWITCH on the probe. You are FAST in replies, I'm a subscriber now! If you have any suggestions what else I could try, I'm all ears. Have a great day!

I've seen the resistors have different colorations, so it isn't necessarily an indication that it is bad. If your resistor is composed of two parts, each one *might* be lower than 500M, so maybe you can measure them individually. As I said, you should be able to test the meter separately to be sure it is right. The one in my meter is a 50uA movement - I don't know what your might be.

Mine say 20 000 Ohms and I think it is working, based on my small experiment. I don't know if I can measure the resistors separately, it seems to me that there is some slick cover holding them together, so I did not want to break the seal (or whatever it is that holds them together). But even per schematics, also in the manual you have included in your reply, there isn't much of parts that can go bad. What I wanted to test is my transformers from couple microwaves that work, but I wanted to see how much high voltage they produce (the specs say about 2200V, but I do not know for sure, since I do not have any other meter that works to double check that). I also made a project from these transformers and it would be nice to have more precise measurements to be sure. Do you think I can safely cut off the cover, that holds the resistors together, so I can measure them individually? You can email me directly to czecht@gmail.com so I could reply with pictures and video. Or if you have Skype, you can find me under: Tonda Fleming (my computer in my hobby room). I want to thank you for all your help!

I would think that they would be much higher than that, which seems to indicate 20kohms. Even 20Mohms would be somewhat small (two of them in series would be 40M, which would result in 2mA of current, which would be asking a 40kV source to provide 80W of power! Maybe they're 20G ohm - that would make more sense, but also make them unreadable with your DMM. Definitely do *not* remove the cover - it is part of the insulation package. Damaging it, removing it, etc. will compromise the safety when using this probe. If you want to measure the output of the HV transformers, try driving them with a lower amplitude input - maybe from a step down transformer, a variac or even a function generator. By driving with a lower input, you can then safely measure the output, which will also be proportionally lower, verifying the ratio of the transformer.

I suspect that the input impedance of your multimeter is changing with the scale setting, which changes the divider ratio. High voltage probes like these are designed for a constant, fixed value input impedance. If your meter doesn't provide that, the readings will be wrong.

***** thanks sir, i figure it out i wasnt connected the ground to the circuit.

+dxdx666 Because it likely also has another resistor shunting the the meter, likely approx 1Mohm.

+w2aew Yes, I agree. My point is that wasn't mentioned in the spreadsheet and you don't mention it in this video too (when describing construction of the probes). The devil is in the details ;)

Some probes, like the one I was using, use the 10Mohm input resistance of the meter as part of the voltage divider.

This probe is probably 30-40 years old, before shrouded banana plugs were used. Also, if the probe were connected to a substantial high voltage source, the shrouds would not be adequate to shield you from the high voltage.

If this is a 50kV probe w/ x100 attenuation, a shroud wouldn't shield against 100s of V? I guess the fact that this is a point probe and not a clamp or clip means it's not as important

The 100x voltage divider is only complete when the probe is connected to the meter. If the banana plug is not in the meter, then the full voltage will appear at the banana plug. No shroud will protect against that.

Ah ofc, thanks.

The cam has stereo microphones, and it was positioned over my right shoulder. That put me closer to the left mic. Doesn't it make it sound like you're sitting next to me? LOL. I'll try to remember to change it to Mono for future videos.

***** I actually find stereo less fatiguing in videos than mono. Maybe because I tend to use headphones and stereo gives a pleasant feeling of a more open space. To each their own I guess! :) Another great video, thank you so much!