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

Roman Sowa modular at go2.pl
Wed Apr 7 10:08:02 CEST 2021


If you don't mind 15% error on a scope then it's fine, I get your point. 
It's easy to check a multimeter just by comparing with another one to 
see if it's way off. And everybody has at least few of them.
Checking if a scope is more or less within specs is not that easy 
especially if old ebay scope is the only one in the lab.

Calibration means it was fully checked and nothing's broken.
Taking that to synth terms - once I have serviced some big polysynth, 
and it was quite OK when finished, but because not so perfect as I 
wanted, I went through meticulous 2-days long full calibration 
procedure. And only then I could find that there were still 2 or 3 
faults, including a need to replace vintage chip being out of specs so 
much that it was impossible to adjust with trimmers.

All I'm saying, there's not much that can happen in multimeter to make 
it lie and not just go dead. But in a huge device like vintage scope 
with crazy high voltages, heat, airflow, early technologies stretched to 
their limits, and who knows what else, there's so many things that may 
drift in time.

Bottom line, in line with yours - for everyday work I use modern scope, 
for fun I use toy handheld scope or vintage one.

Roman

W dniu 2021-04-06 o 23:15, Mattias Rickardsson pisze:
>     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 important.
> 
> 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!
> 
> /mr
> 
> 
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