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How important is 0.5% tolerance to my VOM/DMM

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gooseEL34:
Hey guys.
I am wondering the following....

For checking +15vDC/-15vDC in a solid state guitar amp, is my crappy Fieldpiece Lt16A sufficient with its 0.5% +/- 1 and only a 1/10th of a mV resolution?

Reason I ask is this.  I am a tinkerer with mostly Tube Amps.  I use a multimeter for checking B+ voltages on the plates of tubes (Valves for you across the pond).   I also use it to check resistances and to check if a component is short or open.

I recently started tinkering with a 1970s Lab Series L5 guitar amp which has a bunch of 741 and 4558 ICs.
It seems to have a 15vDC rail and a -15vDC rail.

Assuming my meter is at worst, 1.5% off.   Will I care?  What I mean is: If I read 15.3vDC and it is actually 23mV off,
Can I assume that the rails are supplying normal voltages?

Thanks
Tim

Anyone suggest a meter with 0.05% DC accuracy that isn't over $250??



IanB:
I don't think you need to worry too much about absolute accuracy here. Consistency and repeatability will be more important.

For instance, it doesn't matter much if a 15 V rail is at 14.5 V or 15.5 V or somewhere in between.

However, if you have +15 V and -15 V rails they should be balanced. If you measure 15.3 V on the +ve rail, you should measure 15.3 V on the -ve rail also. This only requires that your meter has repeatable measurements and sufficient precision to compare two measurements.

KJDS:
I suspect that so long as the rails are between 10V and 18V then the amp won't care, so 0.5% will be more than good enough.

In the 70's the person who designed it probably only had an analogue meter for checking voltages that would have been at best 2% and possibly far worse.

alm:
Unless you move both leads when you go from measuring the positive rail to measuring the negative rail, you also need the meter to be symmetric, ie read the same if the leads are reversed. This is more than just repeatability.

IanB:

--- Quote from: alm on February 28, 2013, 08:50:15 pm ---Unless you move both leads when you go from measuring the positive rail to measuring the negative rail, you also need the meter to be symmetric, ie read the same if the leads are reversed. This is more than just repeatability.

--- End quote ---

This is true. I think all of my meters are asymmetric to some degree, but it is more noticeable on the higher precision meters with more digits.

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