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Old 1st Dec 2015, 10:52 pm   #85
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 3,769
Default Re: Test equipment for valve radio repair

One of the many rows I had with the idiot physics teachers at school started when I pointed out that a typical digital multimeter on the 1kV range took twice the current of a typical analogue multimeter on the 1kV range (the former having an input resistance of 10M, the latter, being 20000 ohms/volt having an input resistance of 20M). Said teacher believed that digital multimeters 'took no current'.

Mind you the same teacher claimed that an oscilloscope input was direct to the Y plates and thus had an infinite impedance. Well, a few special purpose 'scopes have no Y amplifier and direct input to the plates but most don't! And even if you do go straight to the plates the impedance is far from infinite (there is the capacitance between said plates for a start).
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