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 1000 Ohms per volt meters
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 Return to top of page · Post #: 1 · Written at 3:56:05 PM on 3 August 2020.
Gandhn's Gravatar
 Location: Windella, NSW
 Member since 5 November 2010
 Member #: 770
 Postcount: 343

Where a circuit voltage chart is provided with other service information, reference is often made to the use of a 1000 Ohm per Volt meter for a very good reason.

I hope my little essay explains why this is so, why a digital multimeter can lead you astray and a simple fudge to help if you only have a newer device.

Harold

1000 OPV


 
 Return to top of page · Post #: 2 · Written at 4:37:57 PM on 3 August 2020.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6352

Document uploaded.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 3 · Written at 5:36:19 PM on 4 August 2020.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 411

Hi Harold,

Well done .... this issue is so easy to forget ... and a good simple 'solution/approximation'.

In general, understanding our how to use a range of Test equipment, its capabilities and its limitations is very a under-rated part of our hobby.

Cheers, IanB


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 4 · Written at 6:20:13 PM on 4 August 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

Yes Harold, that is a good explanation.

My first (analogue) multimeter was 20,000 ohms per volt, same rules apply though.

We should also add that if the circuit specifies measurements taken with a VTVM (as do most vintage TV circuits), that's about the same as a modern digital meter.


 
 Return to top of page · Post #: 5 · Written at 8:40:59 PM on 4 August 2020.
Gandhn's Gravatar
 Location: Windella, NSW
 Member since 5 November 2010
 Member #: 770
 Postcount: 343

Thanks for your positive comments, Ian and Ian.

In a previous life, I spent some 25 years in the test and measurement field, before I was lured into the world of bar code scanning and still have an appreciation for the subject.

Harold


 
 Return to top of page · Post #: 6 · Written at 9:38:40 PM on 4 August 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4345

One can get all meters to lie, if you fail to appreciate how they work and how to apply them. What was used to measure voltages especially in old radios, as noted, is of critical importance. There is a note on one particular early RCA schematic, that states to the effect, "that the voltage measured at a certain point is not that which the Radiotron, is running on". This being the result of circuit loading of the meter used.

Digital meters can be an absolute curse if you try using it on a dirty load like an automotive DC generator. 500 opv AVO is much better. Some have serious issues with RF present on DC as in a Reflexed set. The analogue on DC will not see RF.

Marc


 
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