[Amps] oscilloscopes -- TSPA

["John T. M. Lyles" <jtml@lanl.gov>]

> I'm interested in acquiring a used solid-state oscilloscope for ham use.  I
> know this isn't the place to ask, but hope that people who hang out here
> can point me to a ham radio homebrew or similar mailing list where people
> would have good advice on which models, what to pay, etc.  There are
> skillions of Google results based on searching for the above topics but
> nothing, so far, that looks like the right answer.
> 73, Pete N4ZR


As for a suitable home oscilloscope, I wouldn't even bother with 20 
MHz or 50 MHz bandwidth units anymore. If you can, get 100 as a 
minimum, as they are so easily found anymore.

I used to nurse along an Hp175 monster, wich 4 channel plug in, etc. 
It was a hamfester scope and heated the room with all the tubes in 
it. When i finally solid stated I went to the Tek 7603/7623/7633 
series of mainframes, as they can be found around $100. Having played 
with a few 465 and 466s at work over the years, I was not so 
impressed with ease of service. The 7600 series isn't much better, 
however, but slightly bigger boxes and more spacious inside. These 
scopes require you to pull off a zillion small plugs and wires, to 
remove a board to get underneath where another assembly is hidden.

 I used Nuts and Volts classifieds and bought mine from one of the 
Colorado surplus dealers near Denver. The Tek plug-ins are quite 
diverse in function, and easy to find also. For instance, i have a 
plug in which can be used to measure DC coupled with a high common 
voltage, and has a built in offset that can dial out the voltage to 
see ripple, small noise, etc. Sure you can do this with AC coupling, 
but you also get distortion if you are looking at very low freq 
events through a coupling capacitor. I got the storage frame (7623 is 
fine enough) for doing fast transient work, such as fixing 
photoflashes, and catching glitches. The storage modes are funky on 
these things, but they do work well once you learn how to run them. I 
have a big screen 7603 version mainframe that holds my 7L14 spectrum 
analyzer/tracking gen plug ins and also a 7L5 analyzer for low 
frequency work. The big advantage of 7600 and 7800 series from Tek is 
that they were the first to have built in character generators to 
display the units on the screen. This really helps when you are 
sticking a x10 probe in, as it autoswitches to the correct V/div on 
the screen.

While I love my big Tek solid state scopes, here is a piece of free 
advice. When they have a HV failure, give up and don't try to fix 
them. Too much trouble to get to the HV section.  Also, you can get 
another mainframe for so cheap nowadays. If you live in a humid 
climate (I don't) you should power up the scope occassionally and let 
it run and dry out, as a good HV arc inside can finish the HV 
assembly quick. I have a 7633 carcass thats like that now. Can't give 
it away. Keep the scope clean, around the air vents, and vacuum it 
out once in a while. Otherwise you risk HV failure.

If i was doing it all again, I would look at the Tektronix TDS2000 
and TDS3000 series of 'plastic' portables. They are incredible, and 
we use them extensively at work, up to 500 MHz BW, 4 channels, all 
digital, RS232 or centronics printer output, LCD, color, etc. These 
are in the $1000 and up price range, but you can leave them on all 
the time, and they are small and light for field use. Being a ham, 
though, I understand the need to look for bargains, so I still like 
the old 7600 series a lot. Tek has it hands down over most of the 
older Hp scopes, and both are far ahead of a lot of the Far East 
imports, in terms of quality of components such as switches and pots. 
The first annoyance of a boat anchor scope is the range switch 
intermittant! The second is a HV problems, either bad ripple creating 
a dashed horizontal display, or jumping erratic display or blank, no 
HV.

73
John
K5PRO


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