O-scope question for you old EE's

[Magnus Danielson]

>>>>> "LC" == List, Christopher <Chris.List at sc.siemens.com> writes:

 LC> Quick tool question for you - 
 LC> If you were going to spend $450 on a scope, would you get a brand new
 LC> 20MHz, no frills, LG-Precision or BK-Precision, or would you get an
 LC> older used 50 or 100 MHz Tek or HP with delayed sweep or some other
 LC> nifty things?

It depends on the shape of it, a good shape HP or Tektronix with the
right modules is a good investment. I recon that you would not need to
spend all the $450 on a old scope to get a good one, but you could
surely spend the money on a good set of probes, since these will wear out.

 LC> Any thoughts and/or experiences to share?

Channels, 2 is a minimum, 4 is a releif (I have a 4-channel 50 MHz Tek
547 with dual timebase and delayed sweep that I bought for $25)
anything above that is a blessing.

Speed. You can't get enought of it... well, 50 MHz will certainly be
well enougth for normal audio (and some but not all of the digital one
encounters).

For older scopes there is a few things to consider:

Shape of pots and switches. Nothing will be such a direct anoying
factor as these failing on you. Consider the feasability of having
them fixed or replaced. Some of the switches for a Tectronix is not
easily replaced since they have the full set of adjustable damping
mounted in the rotating part of the switch.

Feasability of getting (good) spare parts. Replacement of CRT and
tubes will eventually become unavoidable and the correct parts is more
or less crutial here. For tubes you may find good replacements I
guess. Otherwise it is the standard refresh mantras such as checking
the electrolyts etc. Getting hold of Service manuals is a great
advantage and try to ensure to get original manuals when possible, the
photos and commented schematics can be most enlightning sometimes.
The Tectronix Service manuals that I have is really high quality stuff
and it is a great enjoyment reading them.

Heat dispantion, weight and space may be issues to consider. My 547 is
a large, heavy and very power-to-heat-efficient blue thing to use, it
works as a tool with its flaws but I rather work with a modern scope
most of the time if available.

Modules. Most of the scopes that you encounter have fixed input
modules, there are more expensive scopes which uses modules that can
have interesting extra modules. I have for instance a couple of
modules that's coarsest scale is 10 mV/cm and then digs deeper down,
this is certainly something that many scopes can't deal with and is
great for noise analysis. The lack of lower end can be quite anoying,
especially in audio when one have large dynamic ranges. Then there is
diffrential modules etc. Some of the diff modules require a diff
probe, be sure to lay your hands on them!

A function that you would not like to be without is XY plot mode, it
is more usefull than one might think. If a scope also has a I/V figure
tracker (easilly built) you have a even more powerfull tool. An I/V
tracker is a very easy way of comparing a point between a working and
a failing board, you may see broken inputs due to ESD etc. However,
few scopes come with this property (the I/V). Few scopes lack XY mode
thought (I have one which is nothing but XY, it does not even have
variable input sensitivity).

Cheers,
Magnus