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Need a new multimeter that goes past 1KV

Discussion in 'Home Brew' started by ElectronTubesRule, Sep 28, 2011.

  1. ElectronTubesRule

    ElectronTubesRule Active Member

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    Ok my fluke is dead and my Mircronta is no better both of them stop at 1000V AC and DC. So I have been scroling through web sites and my eye's are bleeding.....I do not car if it is analog or digital and I am not a brand snob either. The only reason I own Fluke,Wagner,Klein, Milwaukee, and other high end brands is because I was an Electrical Worker and Union at that and we could by tools at cost through the company. They never took much out of each paycheck so as long as you did not quite with a balance their was no interest and no rush to repay.... So I do not care what companies name is on the case they are all made in Korea or China! It just has to have decent resolution and be at least as durable as my Radio SHack Micronta which is better then 15 years old and still going strong unlike my Fluke.

    Ideally I would like something that went up to 3000V ac and DC current up to say not less then 2 amps. Digital or analog and I do not need anything else in it since I have the ability with my other 2-3 multimeters to test diodes, transistors, capacitance etc....Oh I do not care if it is bench top or hand held. I am only going to use it on amplifiers I build for myself and son. So not like I am going to be cranking 100amps a year to sell to people or making house calls....LOL

    Most of the stuff I have seen stops at 1000VDC 750AC....

    I considered using resistor inline but that seems to me like it would not be an accurate way to do things? I am not an electrical engineer though so if that is what everyone else does do give me the low down on how you do it. What I thought about doing was taking a down out from one of the amps I have specifications for and sticking resistors inline until I got a reading of Zero then using that value as a reference point.



    Do they make probes with any type of attenuation factor for use with DMM's???
     

  2. Kamikaze

    Kamikaze Active Member

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    What do others do?

    Spend a little more time asking folks who actually build and use what they built.

    Then spend a little more time figuring out what the voltage will be.

    Since you are building, use a panel mounted meter.

    Poking high voltage should not be necessary.

    Save the Fluke for safer jobs.
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Look on Ebay or elsewhere for a Tripplet 630-PLK but be carefull. IIRC they made two series with the same model number and only one of them had the extended high voltage range.Those meters will have two extra jacks in the lower left corner of the meter labeled "5000 DCV" and "5000 ACV". It will read up to 5000 volts AC/DC and up to 10 amps DC. I have one and it works great. I used it for over 20 years servicing AM/FM broadcast transmitters with up to 4800 volt power supplies. These meters may be old but they still work great and have a nice big meter that is easy to see.


    [​IMG]
     
  4. Kamikaze

    Kamikaze Active Member

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    Your broadcast xmitters did not have working internal meters?
    What would you possibly measure in a broadcast box that factory metering wouldn't cover?
     
  5. Shockwave

    Shockwave Sr. Member

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    If you need to measure thousands of volts, you will either have to buy an old analog meter as has been suggested or another alternative is to buy a high voltage probe for an existing digital meter. They usually divide the voltage down by 10 times. Be careful not to confuse this with a regular "times 10 probe" that was not designed for high voltage.

    With respect to the meters in broadcast transmitters, they do not replace the technicians test meter. Seeing plate voltage on the internal meter only indicates the power supply is producing voltage. It is no indication that this voltage has made it all the way to the tube anode. That requires further confirmation with the external test meter.
     
  6. Kamikaze

    Kamikaze Active Member

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    A condition which can be checked with the circuit cold. Visual for carbon traces and ohm meter for opens.

    Not a good idea to encourage people on a radio interest forum to poke high voltage.

    A little troubleshooting experience will out most high voltage faults without poking around a hot circuit.
     
  7. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    B'cast transmitters have basically a plate voltage meter, plate current meter, an RF ammeter and a multi-meter that is switch selectable from the front panel that reads various currents like RF driver grid current, cathode current etc. Unless you have ten foot long arms or a neck made of rubber it's pretty damn hard to and see the front panel meters while working in the back of the transmitter chasing a voltage issue. Another time they come in handy is when adjusting screen voltages on some transmitters that do not indicate screen voltage and not all of them do/did. Some screen voltages we dealt with were well over 1000 volts and were retrofitted with special jacks to accept an external meter. My personal feelings is that if you even had to ask that question then you obviously have no electronics service experience especially with HV circuits.

    BTW, what would you do if the plate voltage was present on the RF tubes but not on the modulators tubes or vice versa? How would you determine where the fault was if you didn't use a meter to find the problem?

    No, there is NOTHING wrong with poking around in an HV circuit IF you know what you are doing and since I did it for over 20 years believe that I DO indeed know what I am doing.
     
  8. Shockwave

    Shockwave Sr. Member

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    I think you would be surprised to know how frequently you will find an old Simpson or Tripplet VOM in the arsenal of tools used by those who service larger transmitters. There are plenty of situations where the fastest way to spot a problem requires confirming the actual voltages present at various points under power. It is not uncommon for a service tech to have to defeat safety interlocks to temporarily connect the meter directly to places such as the tube socket. Many things can be checked cold, but others such as setting voltages that control currents cannot. Captain points out one classic case of the screen voltage on broadcast tubes and that just involves routine maintenance. Complicated troubleshooting often benefits from the educated hands on approach. The only danger is doing this without complete knowledge of where the high voltages are present and knowing how to safely avoid a shocking experience.
     
  9. ElectronTubesRule

    ElectronTubesRule Active Member

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    Well I have to know how many volts and what the current is on my high power transformer's. They are not labeled and they are NOS from the 1980's from a company that went out of Business making Class D amplifiers. I am not going to build my doubler blindly with out knowing what my starting voltage and current is that would be foolish as can be!!!!Like wise I need to know what I have coming out of the doubler under test conditions before I ever even consider installing it in the chassis and hooking it up to the other parts!

    I believe in being very safe and thorough. I would never blindly put anything into a HV circuit with out first checking it completely outside of the chassis! I am a risk taker but I am a calculated risk taker not a Kamikaze and I value my life. I even believe in pre-checking parts before soldering into anything. Nothing takes longer then to have to do a job twice because you rushed and did not check the details!

    What happens if my transformer put's out 2000Volts @ .500 amps and I build my doubler assuming it put's out 1000 @ .800ma???? I could not only blow my dubler but if anything else is hooked to it expecting to see 2500V output and instead it is seeing 5000V guess what???? I just destroyed everything after that because I did not have the ability to test past 1000V and made stupid assumptions based on what I wanted not what I had!

    To be quite honest even if these transformer's had come from say Peter Dahl I would still want to test them before putting them int he circuit. People make mistakes all the time even professionals this is why Surgeons have to have malpractice insurance and I dare say surgeons have more school time and training time then the guys winding transformers! So if someone with 12-16 years of college and 2-4 years of internship depending on what they are wanting to do can make a mistake anyone can! So even if I was apprenticed under say CaptinKilowatt that would not make me any-less likely to make a mistake and watching him do something again while very instructive again would not mean I am some how less prone to screw up!!!

    Observation with out quantifiable data is almost worthless. So first you must have a means to measure that which you observe! I can not measure anything above 1000V right now. That is a problem in my book.


    Thanks guys....I will take a look for that meter.
     
  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Oh I remember defeating the safety interlocks on more than a few occasions. One time comes to mind when I was checking out an old Gates BC-1T that kept mysteriously blowing the 30 amp line fuses. Upon arriving at the tx site to put it back on the air all one would have to do was install new fuses and it worked fine. That was until about 2:30 or 3:00am some morning down the road when it would decide to fail again. :censored: BTW this TX was over an hours drive from home.One such callout had me standing in front of the transmitter with the front door wide open and the safety screen removed and a pair of small metal tangs inserted in the interlocks to defeat them. This allowed me a clear view of whatever may be wrong as I repeatedly engaged the PLATES ON button looking for flashes, arcs, etc. Here is the good part. The big old contactors in the TX would engage with a noticeable "THUNK!" and you could feel a small vibration if you felt the cabinet. The front door latch was spring loaded. After repeated "THUNKS!" of the plate contactor the door latch let go with one hell of a "BANG!!!" as it slammed against the big solid steel door panel the very instant I hit the big PLATES ON switch again. I almost dropped a load right there. :eek: I still don't remember hitting the OFF button but apparently my reflexes are better than my memory. :D
     
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  11. Shockwave

    Shockwave Sr. Member

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    For simple voltage testing of plate transformers there is a safe and easy way to do it. Whatever the rated primary voltage is, apply 10% of that rating. For 120 volt primaries, just feed it with a 12 volt AC transformer or a variac set at 10%. Then you can use you existing meter and be working with a few hundred volts on the secondary rather then a few thousand. Multiply your output by ten times and you'll have your unloaded AC secondary voltage.
     
  12. ElectronTubesRule

    ElectronTubesRule Active Member

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    CaptainKilowatt I have found and purchased that model. The image has the two extra ports on the lower left and it clearly reads 5000ACV/5000DCV!!! Thanks for pointing me in that direction. I spent hours on google trying to locate 2000 Volt, 3000 Volt, High Voltage and permeation their off.... It was a long night that was not at all productive....Thanks!


    It is NOS still has the OEM bar code pick tag on the meter front and on the matching leather case! $42+$15 for shipping! It is exactly what I was looking for but did not know existed!!! Thanks so much!

    So when I go to test the transformers ouput should I put some resistors in line or do anything in particular to test it under load or is a no load power reading sufficient for calculating and designing the rectifier/voltage multiplier.
     
    #12 ElectronTubesRule, Sep 28, 2011
    Last edited: Sep 28, 2011
  13. Shockwave

    Shockwave Sr. Member

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    The no load voltage of the power supply is ideal for determining the required voltage of the caps and diodes since it will be highest then. Just be sure you understand that the DC voltage is going to be 1.414 times the AC for full wave and 2.828 times the AC for a voltage doublers. Diodes should be rated for twice the inverse voltage since there will be that much present when the diode is not conducting.
     
  14. ElectronTubesRule

    ElectronTubesRule Active Member

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    Thanks!!!
     
  15. Kamikaze

    Kamikaze Active Member

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    Any situation where one would want to defeat an interlock and probe a transmitter's B+ supply can be replaced by advanced troubleshooting skills period.

    The only time high voltage is necessary for component testing is when looking for hi potential insulation breakdown. This test can be facilitated using a hipot tester which is current limited.

    Your example CK.... Your am transmitter has B+ on the rf amp but none on the modulator? Look and smell for burned parts, loose connections then check the modulation transformer primary with an ohm meter. If the transformer and associated wiring seems OK take a bench DC supply and short across the primary center to one plate terminal at a time. Turn the supply up until it draws enough current to simulate the average modulator plate draw and look for intermittant drops in current from an open. If the situation is reversed B+ on the modulators but none on the final substitute modulation reactor where I wrote modulation transformer above.

    This is 2011. Any company who employs someone who does hot work exposes themselves to unnecessary financial risk. This is especially true where work arounds are well known. Even a website like this could be a target of a lawsuit if some yahoo gets fried. You guys do give some good advice on occasion but dropping the "I used to be a broadcast guy" and advising someone to measure dangerous voltages is a a really bad idea IMHO. Sorry for my tone but I had one friend who is disabled due to a hot work accident. He was lucky. Another guy I used to talk with was electrocuted while measuring the B+ in his newly built Heathkit 3-500 amp. I'm sure VA3ES remembers him too. Think of the horror and danger to family members who have to deal with the aftermath of such accidents.

    For builders unknown transformers can be checked by powering with a filament transformer and scaling the readings up. If you cannot apply the formula for cap input or choke input and come up with decent accuracy for the voltage in a new circuit it is time to put down the tools and hit the books.
     

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