[sdiy] HP 54602B selling on eBay.. DC vertical offsets on some channels or what ??

Mattias Rickardsson mr at analogue.org
Tue Apr 6 23:15:28 CEST 2021

> unless it comes with a current (less than a year old) calibration
> certificate add the bucks it costs to get calibrated it professionally if
> you want accurate measurements.
The importance of keeping your old measurement gear calibrated is sometimes
mentioned when discussing old scopes etc on this list.

I must say that I'm still waiting for the moment when I actually need the
level of certainty that a freshly calibrated unit brings, even in serious
product development. Having a serious multimeter and a
great soundcard+audioanalyzer is much more important, and takes care of
many of the tasks that a well-calibrated oscilloscope traditionally would
be needed for.

My impression is that c:a 1980s' scopes in good condition are often close
enough to the correct values. Even my old scope's built-in DMM always gives
the same reading as my modern Fluke, so I never worry about using it. (I
can only speak for Tektronix scopes, btw, I'm sure there are many
brands aging less charming.)

90 % of the times I use an oscilloscope, it's just for getting a glimpse of
a waveform or two, perhaps also the level, period, timing... but just for a
rough view, it wouldn't matter if the readings were 15 % off. Sometimes I
don't even notice that the red "CAL" knob top is a bit off from a previous
measurement, because it's not important.

9 % of the times I use a scope I need to measure some signal level or
waveshape seriously, but only in relation to another signal or voltage that
is also available for probing, so the absolute precision still isn't

The remaining 0.99999999... % of the times I use a scope... hmm... I do it
just for the fun of it! :-)

That said,
- When I need to measure or compare audio signals and spectra on a more
serious level, I do it with an audio interface on my PC.
- If I were to write technical reports about the products developed, I
would then need - and buy - and use - an Audio Precision system.
- If I were to write research papers, I would THEN need the precision of a
calibrated unit - but then I'd also not shop around for old scopes but buy
a new one. Which I would likely never send away for re-calibration.

To sum up, we live in great times - when old scopes don't necessarily need
to be stellar performers, and when decent new scopes are cheaper than ever!

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