Russell wrote:
Would be curious about thoughts from others who repair their own
gear about what minimum-required scope would be.
This topic comes up periodically -- you can find some posts in the
archives. Here is what I wrote in July 2010, with some further
comments in brackets:
You will likely get a variety of responses. Here's my tuppence worth:
As far as features and capabilities, a fully-featured scope will do
things you don't even know yet that you will want to do, and you'll
be very glad you got it when that time comes. For the most part, you
can just ignore the fancy features until you need them. The work-
horse has, for many years, been the 100 MHz dual-trace "portable"
bench scope with delayed sweep -- with very good reason. This
instrument can do the vast majority of what anyone needs, and they
are plentiful so prices are reasonable.
First-quality scopes (Tektronix and HP) are available used for very
little money these days, so IMO anything less (Leader, B&K, etc.)
should only be considered if it's free. '80s- and '90s-vintage
scopes are cheap and plentiful, so there is no need to look at '70s
and earlier Tek and HP models, either. [There were some decent
models from Hitachi, Kikusui, and Philips, but they are all a full cut
below Tek and HP. I used to recommend the old Tek tube scopes,
but they are old enough now that you will spend more time fixing
them and chasing down intermittents than using them on other
equipment, and some parts are devilishly hard to obtain.]
I am very partial to the HP 17xx series -- my 1742A, which I
originally purchased new in 1982 and which was on and working 10-12
hours per day for its first 15 years, still meets its specifications
and the screen looks as new. IME, HPs are generally easier and less
costly to repair than the equivalent Tektronix models (the Tek 465
series is particularly difficult and costly to repair). A
properly-working HP 1740A or 1742A can be had for $50-150. Even a
properly-working Tek 2465A digitally-controlled analog scope
shouldn't run more than $200-300 (the 2465Bs cost more because they
were the last of the line, but they aren't any more capable).
So, unless the budget doesn't extend as far as $100, I'd get a 100
MHz dual-trace HP or Tektronix from a reputable seller.
Most people use 10x probes almost exclusively, but for completeness
you'll probably want a couple of 10x and a couple of 1x probes. IMO,
name-brand (Tek or HP) probes are well worth the money over generic
probes. If you shop carefully, you can get good ones for $15-25 each
(though you'll see many listed for ten times that). Make sure the
compensation capacitor range on the 10x probes matches the input
capacitance of the scope (this is generally clearly marked on both
the scope and the probe).
These days, you will also find digitizing scopes in the $200
range. However, to get similar performance (>/= 50 MHz "one-shot"
capability) and quality to the analog scopes mentioned above, you
would probably need to spend $400-$900 (the Tek TDS2xxx scopes would
be the ones to look at, IMO).
The Rigol digitizing scopes have also been very popular lately. Note
that most digitizing scopes put out all kinds of RF garbage, so they
may not be suitable for working around receivers. Also, due to the
limited bit depth of the A/D converters and low screen resolution,
affordable digiscopes have noisy traces. On the other hand, you can
make all kinds of measurements on the waveform, and often get a crude
FFT of the input. And many of them will output to a thumb drive
and/or computer so you can save copies of the data and/or traces easily.
Asking prices on ebay for all of this stuff vary all over the map,
and by far the large majority of listed items do not sell for their
ridiculous minimum bids or reserve prices (check the "completed
items" view to see what sold, and for how much). I have had
reasonable success contacting sellers after their items were up for
several cycles with no bids and making much lower offers.
As always, it pays to study the instruction and service manuals for
models you are considering, so you can interpret the listing photos
properly and ask any questions you need answered to help determine
the working condition as best as you can from a distance.
Finally, let me stress once again the importance of good probes. You
may need to wait a while to get genuine Tek or HP probes at a good
price [$15-35 each, complete with ground leads and spring hooks], but
the effort will be well worth it. Make do with some cheap
substitutes (Pomona, etc.) until then.
Best regards,
Charles
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