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#1
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Homebrew 3kV Power Supply
I recently got a high voltage transformer that I'm going to use to build a
HV power supply for some future homebrew tube amps. I'm curious if I'll need a high voltage voltmeter? I'm new to the high voltage world and so need some guidance or 'tips' in building HV circuits. I have already consulted the ARRL Handbook for all of the safety precautions, so I'm not so much looking for that sort of information, as I am practical tips in putting together the circuit and having some sort of meter to use in order to check various voltages throughout the circuit & on the output. If I do need a voltmeter capable of measuring kV level voltages, what brands/models should I be looking for? If not, what equipment will I need? Thanks, Jason KB5URQ |
#2
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I'd add a caveat that when dropping down from
the high voltage, do it with a chain of series resistors, each physically separated from its neighbour so that you don't get flash-over. i.e., restrict the voltage over each resistor to less than a couple of hundred. "Bill Turner" wrote in message ... On Sun, 23 Jan 2005 19:39:41 -0600, "Jason Dugas" wrote: If I do need a voltmeter capable of measuring kV level voltages, what brands/models should I be looking for? If not, what equipment will I need? You don't really need a high voltage meter per se. If you think about it, the current through the bleeder resistors is directly proportional to the total HV, so all you need is a low-value 'sense' resistor at the bottom of the string, and then measure the voltage across it. The only tricky part is compensating for the loading effect of the voltmeter across the sense resistor, but even that is basic ohm's law. |
#3
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Carbon composition resistors are not linear above a few hundred volts.
There are resistors specifically designed for this purpose. You can also purchase Fluke, Heath or Eico HV probe on EBay for about $20. If you are building a high voltage supply I would strongly urge you to take a look at some of the supplies manufactured by Collins, Heath, Hallicraftes, Drake etc. in the 1960's and 1970's -- there are several layers of protection, failsafe and redundancy in all the power supplies for their amplifier so that the operator wouldn't fry themselves. "Airy R.Bean" wrote in message ... I'd add a caveat that when dropping down from the high voltage, do it with a chain of series resistors, each physically separated from its neighbour so that you don't get flash-over. i.e., restrict the voltage over each resistor to less than a couple of hundred. "Bill Turner" wrote in message ... On Sun, 23 Jan 2005 19:39:41 -0600, "Jason Dugas" wrote: If I do need a voltmeter capable of measuring kV level voltages, what brands/models should I be looking for? If not, what equipment will I need? You don't really need a high voltage meter per se. If you think about it, the current through the bleeder resistors is directly proportional to the total HV, so all you need is a low-value 'sense' resistor at the bottom of the string, and then measure the voltage across it. The only tricky part is compensating for the loading effect of the voltmeter across the sense resistor, but even that is basic ohm's law. |
#4
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That's news to me! Would you care to expand on it?
If one could look at a carbon atom in isolation, how is the conduction mechanism changed by the size of the applied electric field? "John Walton" wrote in message ... Carbon composition resistors are not linear above a few hundred volts. There are resistors specifically designed for this purpose. "Airy R.Bean" wrote in message ... I'd add a caveat that when dropping down from the high voltage, do it with a chain of series resistors, each physically separated from its neighbour so that you don't get flash-over. i.e., restrict the voltage over each resistor to less than a couple of hundred. |
#5
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Are these "HV probes" simply high voltage voltmeters?
"John Walton" wrote in message ... Carbon composition resistors are not linear above a few hundred volts. There are resistors specifically designed for this purpose. You can also purchase Fluke, Heath or Eico HV probe on EBay for about $20. If you are building a high voltage supply I would strongly urge you to take a look at some of the supplies manufactured by Collins, Heath, Hallicraftes, Drake etc. in the 1960's and 1970's -- there are several layers of protection, failsafe and redundancy in all the power supplies for their amplifier so that the operator wouldn't fry themselves. "Airy R.Bean" wrote in message ... I'd add a caveat that when dropping down from the high voltage, do it with a chain of series resistors, each physically separated from its neighbour so that you don't get flash-over. i.e., restrict the voltage over each resistor to less than a couple of hundred. "Bill Turner" wrote in message ... On Sun, 23 Jan 2005 19:39:41 -0600, "Jason Dugas" wrote: If I do need a voltmeter capable of measuring kV level voltages, what brands/models should I be looking for? If not, what equipment will I need? You don't really need a high voltage meter per se. If you think about it, the current through the bleeder resistors is directly proportional to the total HV, so all you need is a low-value 'sense' resistor at the bottom of the string, and then measure the voltage across it. The only tricky part is compensating for the loading effect of the voltmeter across the sense resistor, but even that is basic ohm's law. |
#6
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Airy R.Bean wrote: That's news to me! Would you care to expand on it? If one could look at a carbon atom in isolation, how is the conduction mechanism changed by the size of the applied electric field? The paint on the resitors is not a perfect insulator - it breaks down as the voltage increases. This is why there are high voltage resistors. Not rocket science exactly. And if you are going to stuff around with HV, make sure there is someone aound who can do CPR when you fry yourself...... 73 de VK3BFA Andrew |
#7
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On 25 Jan 2005 05:52:49 -0800, "Andrew VK3BFA"
wrote: Airy R.Bean wrote: That's news to me! Would you care to expand on it? If one could look at a carbon atom in isolation, how is the conduction mechanism changed by the size of the applied electric field? The paint on the resitors is not a perfect insulator - it breaks down as the voltage increases. This is why there are high voltage resistors. Not rocket science exactly. And if you are going to stuff around with HV, make sure there is someone aound who can do CPR when you fry yourself...... 73 de VK3BFA Andrew I don't buy the paint theory much . . . The original answer specified a few hundred volts per resistor and that isn't exactly high voltage . .. . The common radio shack flame proof 1/2 or 1 watt sizes would be my choice for ruggedness. A long time ago I repaired vacuum tube TV sets. I'd find an occasional high value resistor with a short in it, or very lower than tolerance reading. These were usually high value resisters with relatively low current, across higher voltages ~400-500 and up. When I asked about it, I was told that when resistors dropped high voltage DC (these were carbon comp 10%'rs - back then) for long periods of time, the copper in the leads migrated into the carbon and lowered the resistance. In the case of something like a screen resistor - it could go for quite some time before it caused a noticeable problem - or at least severe enough for the customer to have the set looked at. It was a frequent problem in the old tube type CB transmitter output stages - so RF may have accelerated the problem? I have an old "boat anchor" style variable HV supply I picked up at a ham fest. It has a 100 ua meter on the front measuring the 1 KV output. The dropping resistor is part of the bleeder string - six one watt resistors. Stay safe. If it can kill you - respect it. I saw one of my colleagues take a hit from an ancient high power Navy AM transmitter. The thing had every safety device imaginable on it (in fact the safety interlocks were the most troublesome part of the devices). He followed protocol and picked up the shorting bar in the compartment and put it to the HV caps - no arc so he assumed it was safe (it had crowbar relays that short the supply when the covers are removed, the shorting bar was extra safety). He took it from his hand on the shorting bar (the ground was broken). A spark shot from his ass to the scope cart behind him. He suffered no physical damage - but he went into shock and wouldn't go near that transmitter again. |
#8
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The original rectum-frier, no doubt.
Which reminds me of the article I found and appended..... "default" wrote in message ... A spark shot from his ass to the scope cart behind him. -----OOOOO----- In article , writes... Hi, Would you please tell me what transistor do and how to do so? What is the difference between PNP transistor and NPN transistor? What is the concept of using a transistor as a switch? Thanks a lot. SemiConductor Theory -------------------- (c) 1997 by Gareth Alun Evans A transistor is rather like the human alimentary canal, after the typical USA diet of burgers and chips; - it constipates, as do semiconductor diodes with no applied bias - the available holes get filled in and nothing can move. The base current is like a small application of laxative; some of the constipation passes through, until the effect of the laxative wears off. The total throughput depends upon the Mobility. By applying a continuous feed of laxative, then a continuous current passes through. Applying too much laxative results in saturation - ie, there is a limit to the maximum throughput, depending on the external circuit; in this case, the maximum rate at which you can feed in the burgers at one end. (If you are a customer of MacDonalds's, here in Chippenham, Wiltshire, UK then this rate is very low - I have been there twice, and both times, the service was *APPALLING*.) The difference between PNP and NPN is the direction. In the old days, PNP was used, whereby one injected from the rear end, using a sort of huge syringe - hence PNP - "Put-in Near Poo". More recently NPN is more common, where the laxative is entered via a carrier of some sort, usually chocolate and so we have NPN - "Now Pleasant Nutrient". Despite the adverse effects, the USA diet of burgers and chips carries on, and recourse has to be made once again to the chocolate. Now the ratio of the carriers of the constipation, the burgers and chips, is much higher than that of the chocolate. Thus they are referred to as the Majority Carriers and the Minority Carriers. If you indulge too much, you find that the vendor will provide you with a paper bag, known as an Excess Carrier. More recently, there are problems with impurities and you find that the opposite effect occurs. You have no time to reach home before diarrhoea takes over. You have no option but to stop the car and nip over a gate into a field. Hence the Field Effect Transistor. This time you have to inject something to STOP the flow. Now, assuming that there was a certain control over events; nothing happened until the Gate was encountered, you then became the Source of flow, and the field itself acted as the Drain. What was originally dirt, became grass, was consumed by the Cow, you ate it as a burger, and it has now returned to the topsoil, an effect known in the trade as Surface Recombination. (Incidentally, did you know that Diarrhoea is hereditary? Apparently it runs in the jeans.) Some of the impurities accumulate in your rear end, and no matter how valiently you try, you cannot rid yourself of them. Hence In-de-Bum is known as a Try-Valient Impurity. In the same way, Arse-nic, well known for its ill-effects and accumulation in the body tissues is known as a Pent-Up-Valient Impurity. -- 73's etc de Gareth G4SDW (nee G8DXY) GQRP 3339 |
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