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-   -   Hickok tube tester calibration help needed (http://www.diyaudio.com/forums/tubes-valves/135385-hickok-tube-tester-calibration-help-needed.html)

tc4all 25th December 2008 12:26 PM

Hickok tube tester calibration help needed
 
I am not he most electronic literate but do try hard. I have a 6000A that is calibrated and now am trying to calibrate my 533A. Filament readings are right on, but my DC volt reading should be 190 +/-2, but it is 202. Calibration instructions say to adjust the meter magnetic shunt if it is a minor difference or the resistor R24 if major. I would think this is minor. Is the shunt the band of metal around the meter body that, by loosening a nut I can vary by about 2 inches? If so, moving that does nothing and it is not magnetic. What have I got wrong here? Any help would be greatly appreciated.

HollowState 25th December 2008 05:12 PM

I think a 10% difference is a little more then minor but not so much more. The metal slider on the meter is steel and shunts the movement's magnet which is inside. It's adjustment is only for very small amounts, like a few pointer widths. So you may need to adjust R24 as read.

Audioxpress website has a very nice article for download listed under Web-exclusive Articles titled "Calibration of the Hickok 539C Tester". Since this model is similar in function to your 533, it may be of some help. It will give you a good insight to the workings of your tester. I'll try a direct link to the PDF file. If it doesn't work, go the their website and follow the above route.

http://www.audioxpress.com/magsdirx/.../schoo2798.pdf

Victor

Zero Cool 26th December 2008 06:04 AM

you must use a 1000 ohms per volt meter. If your using a Digital meter then all your readings will be high.

You can add a resistor in parallel with your meter leads to load the circuit. For example my Fluke 189 has manual ranges of 5, 50, 500 and 1000 volts. So i use a 5K, 50K, 500K and 1meg 1% 1/2 watt resistors in parallel.

I configured some dual banana plugs with the resistors so i can just plug in whatever value for what ever range im working with.


Zc

tc4all 12th January 2009 01:50 AM

Not sure if multimeter is right
 
Thanks for the help. Now that the holidays are over I got back to this and read the article. The tester I am using (Micronta 43 range multitester) says 50,000 ohms per volt (DC) on the outside of the box. There are many ranges to choose from, but that is the indication on the box. Would this mean this will not work for the calibration?
Thanks
TC

llwhtt 12th January 2009 02:48 AM

Yes you can but you'll have to add some resistance in parallel with your leads. You are trying to read 190 volts and I imagine your meter will be on the 250VDC scale. So with the meter on the 250VDC scale your meter will load the circuit with 250 times 50,000, or 12.5M Ohms. The alignment procedure assumes the meter is 1000 Ohms per volts, so on the 250VDC scale the circuit will be loaded with 250 times 1000, or 250K Ohms. Do you see the difference? This is why your readings are so high. What you need to do is figure out what resistance in parallel with your meter will get you 250K Ohms. Then get some 1% resistors for each of your different scales, whatever they are. On the 2.5VDC scale you want 2.5 times 1000, or 2.5K Ohms, 10VDC scale you want 10 times 1000, or 10K Ohms, etc. I've aligned many TV-7 testers with my DMM with these parallel resistors and it works great, easier than finding a 1K Ohm per volt meter!!!!! This pretty much Zero Cool said by the way. Oh, in case you didn't catch it the lower the resistance the greater the load (more current) and therefore lower voltage.

Craig


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