measuring very high resistance

[unclejed613]

i forget which monitor manufacturer it was, but even with a diode split winding on the flyback, they tapped the focus and screen divider from the anode voltage. those flybacks had a distinctive failure mode..... the anode voltage would arc from the top of the focus pot assembly to the nearest piece of heat sink (the one for the horizontal output transistor). triplers were most common in sony tv's and rear-screen projo tv's. the HV wiring got really interesting in projo tv's that used distribution blocks to split the HV 3 ways. the tv would have a rather large flyback, then the HV wire from that would go to a distribution block and 3 HV wires came out of that to go to the tubes. others used a tripler with 3 HV wires, and still others used 3 separate flybacks.

when i was young, flybacks were not encapsulated in plastic, and had a separate rectifier. i used to have piles of 1B3 tubes when i was a teenager, as well as 6DQ6 tubes (the horizontal output tube that was most common). later the tube was replaced by a silicon rectifier, but the flyback was still "open frame". eventually somebody figured out that they could put diodes between each "pancake" and encapsulate the whole thing.

 

[tcmtech]

I liked those old open frame fly back coils! They were my first HF high voltage source I ever made. I just used a simple 12 volt self oscillating push-pull circuit on a hand wound primary.
I could easily get a solid coronal discharge that was a good 1/2 inch thick all the way around the secondary on some of the fly backs! And pull an arc a good 3+ inch's off the HV lead!

 

[unclejed613]

i used one with the same push-pull circuit to make an ozone generator. the actual ozone making element was a piece of stranded wire soldered to the high voltage lead at one end, and the strands spread out in a fan shape at the other end, and a piece of grounded pcb about 1 or 2 inches away from the open end of the strands. a computer fan would blow air through the ozone assembly. it didn't generate enough ozone to cause headaches, but enough to deodorize the air on a small production floor. i had to replace the corona electrode about once a month, because the stranded wire would oxidize rapidly and the wire would turn to green dust. you could see the blue glow at the ends of the strands from a few feet away.

i remember i had to "fudge" the bias divider for the bases of the transistors because the simplest push-pull driver circuit i had was designed for germanium transistors. IIRC the oscillation frequency was about 1Mhz. i recently built an ionophone using the same circuit, and modulating the +12V with audio. an ionophone is a "speaker" that has no moving parts. the audio modulated corona discharge generates pressure variations around the discharge that is audible as sound. the modulation is accomplished by putting an audio transformer in series with the 12V input to the push-pull circuit and feeding the transformer with a few watts of audio.

 

[tblo163]

Just a thought! I had a similar problem with 0ne of my multimeters,it would not give an accurate reading when testing resistance.The problem was caused by constantly testing HIGH dc amps,the probe wires had built up a higher resistance than normal.when touching the probes together (coninuity mode) it showed a much higher reading than it should have.I substituted the leads and it was fine again,when these leads build up this kind of resistance,they are useless,and only fit for the re-cycle bin,
GOOD LUCK TERRY

 

[unclejed613]

i used to trickle charge car batteries with a 12V open frame supply that had foldback current limiting. i had some 18ga clip leads i used between the power supply and the battery. the power supply was current limited at 6A. one time i had lost one of the 18ga leads, and without thinking used a 22ga lead instead. i came back a few hours later to find that the battery voltage had only gone up to 5V from the original 3V. the 22ga clip lead had burned open right at the crimp on the alligator clip. i found the original 18ga clip lead and put it back and finished charging the battery. after that i began soldering the ends of clip leads when i get them. the crimps have enough resistance in them to cause problems with high currents, and i suspect many ohmmeter leads are crimped as well.