Vintage equipment voltage measurement

Put the appropriate resistance across the test leads.

Cursitor Doom wrote

If it is available look a the circuit under test, and see if the high impedance does make a real difference.

Else use the scope probe... Do not some of them modern Di Gital makes also display volts? If meter impdance is too high and no other way add a resistor in parallel to your meter?

100-200k is 5-10v scale on a 20k/V meter. Or use a digital & add your R. High R meters give a more realistic reading than old analogues on high R circuitry.

NT

Why not ignore the voltage notes and just fix it?

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

You're obviously not a service engineer. ;-)

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Oh, I see. I didn't quite understand what Clive was getting at. Would that do the trick, d'ya rechnung?

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I'm an engineer, not a service technician.

This is an electronic design group. I think there is an electronic repair group. The engineering approach to fixing things is to probe around, understand how it's supposed to work, and figure out why it doesn't.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Spot on!

Good Lord!! I've only been reading your comments on this group for the last 20+ years and never really noticed that before! ;-)

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This thread is cross-posted to both ...

What's so hard about putting a resistor in parallel with your meter?

The engineering approach to climbing Mt. Everest is to find out where it is. Learn to climb stuff. Get a bunch of money. Buy the stuff and hire the people you need to climb it. Go to where it is. And then climb it using the stuff.

Never even occurred to me.

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That's what you get when people lack basic understanding of the matter.

Resistance used depends on the range:

better explanation:

John

I've only recently discovered that I invariably overlook simpler solutions. Fortunately I'm only a hobbyist and don't do this for a living!

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This message may be freely reproduced without limit or charge only via  
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And that is clearly true for more than just electronics!

Or you could just read the question:

I'm currently TS on a mid 70s Tek scope the manual for which states the readings given are valid for a meter with a Zin of between 100k and 200k (specifically a Triplett 630NS see link).

Even better would be to understand why they specified VOMs with 20k/V sensi tivity, and the implications with modern instruments.

Back in those days, the commonly-available multimeters were 1k/V and 20k/V VOMs and 11 Meg VTVMs. The cheaper 1k/V would load down the circuit and gi ve an erroneously low voltage reading. With the 20k/V VOM and the VTVM, th is error was usually smaller than the inaccuracy in the analog meter moveme nt.

Resistors had 10%-20% tolerance, and the power line voltage could easily va ry by 10%, so the values in the service manuals were approximate, not a spe cification with a precision of 0.1V. Significant discrepancies could be a hint of the source of a problem (for example, a positive voltage on the con trol grid and a very low plate voltage might be due to a leaky coupling cap acitor).

A modern DMM without modification is fine as it is if you understand what y ou are doing.