[Test-Equipment] Advice about used scopes

[Chris Albertson]

Thanks a bunch for all the info.  Disagreements are good.  Let's us see
both sides of a point of view.  As for my use of the scope.  I do want
to be able to look at the waveform from  radio transmitters that works
at frequencies of up to 50Mhz.   I need to be able to design and test
RF transformers and RF mixers and filters at frequenies up to 50Mhz.  I
want to see what is being sent to the antenna (or more likey dummy
load)... A 20Mhz scope may not work for that

As for measurements.  My guess is that any used scope will not be
calibrated well and the cost to calibrate it would be more than the
scope is worth.   I'm working on getting (building actually) a
frequency counter and a peak indicating RF voltmeter  I figure a used
scope is for making relative measurements, comparing signals and
looking at the shape of waveforms (is is clipping?)

My budget really is "$100 and up""  not "about $500".

Now, after reading some downloaded manuals,  I understand the
serviceability of the older analog  4xx scopes.  I've skimmed over the
service manuals and I think they are well written and I might be able
to do some simple maintenance on those "portable" scopes.

Question:  What fails on the 7000 series scopes?  I had the idea that
maybe I could get a 7904 and a good sock of spare plug-in modules.  If
it's the modules like the vertical amp and the time bases that go out. 
They sell for cheap.  I could buy two (or three) of everything.  But if
it's the mainframe itself, well I guess they are cheap enough I could
keep spares too but storage space is an issue.

One more question:  The 7904 has two vertical amp bays.  Do I
understand this right?  With an amp in each bay I could have a dual
trace scope.  Or with a dual channel amp in one bay I could have a dual
trace scope.  What do I get by placing two dual channel amps in each
bay a four channel scope?.  I've also seen scopes with two time base
units.   I've not found this covered in a Tek manual , yet.

The 7000 is looking good _if_ my plan of stockpiling spares would  work
but just getting a 465 seems simpler and will do what I need.  Maybe
buy a "parts" 465 to keep in the closet.





Chris Albertson
  Home:   310-376-1029  chrisalbertson90278 at yahoo.com
  Office: 310-336-5189  Christopher.J.Albertson at aero.org

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