View Full Version : Oscilloscopes, Oscillators, etc

louped garouv
05-10-2007, 02:51 PM
So I stumbeled over some "ancient" test equipment... :)

a HP 233A Audio Oscillator and a

HP175A 'scope with the
1780A AUX plug in (single or normal sweep, manual or external arming) and 1750A dual trace vertical amplifier plug in (dual trace and differential display, .05 v/cm to 20 v/cm sensitivity, 9 nsec rise time (DC to 40 mc bandwidth))

and a manual....

and a DEC H758-a power supply

what exactly would this type of stuff be used for? and can i kill myself tinkering around trying to learn to use it?

05-10-2007, 03:51 PM
and can i kill myself tinkering around trying to learn to use it?

Depends on where you stick your probe... but yes, you can.

Could be useful as general purpose electronics test equipment
if in working condition.
Read some books, take some courses, be safe. :) -grumpy

louped garouv
05-10-2007, 04:00 PM
starting out with the manual...


then on to web research...

05-12-2007, 08:49 PM
Yes, there are folks who restore old test gear much like the speaker folks here. The problem is that the investment and labor required is usually much higher due to the *very* specific parts involved and the alignment usually required after any restoration/repairs involved.

For the oscillators, its important to look at alternatives provided by your PC and an external sound card. You can find a signal generator in software to drive your sound card that will usually generate less distortion than one of the old oscillators - and you'll be able to get it set right on frequency easier, too.

For the 'scopes, these are trickier to restore and can be costly - especially if you don't do the work yourself. The alternative here is to purchase a decent little scope for $300 or so, which would be less than your restoration costs if you have to have someone else do the work.

HP made great gear but they were designed for engineers by engineers. I know as I spent the past 20 years of my career with HP. This means that most of the operation manuals were written assuming you know something about why you're using the gear. If this isn't the case, then perhaps you'll need to do some education for yourself.



05-13-2007, 01:57 PM
I don't know the scope model number but a couple of things to know are that the rating on a scope is the point at which it will be 3db down. The same is true for the probe. So a 10 meg scope with a 10 meg probe will be 6db down at 10 meg. meaningless at audio frequencies. More important is that the probe ground is ground and this can cause a lot of trouble. You should get an isolation transformer to plug the scope into if the ground lead will ever need to be hooked to something that shouldn't be grounded and it almost asuredly will. Any transformer with two 120v windings can be used as an isolation transformer so you should be able to find a suitable transformer surplus and/ or used very cheap. You need to insulate the case of the scope also. Safer is to use an isolation transformer on whatever you are testing but this can call for a much larger and expensive transformer. HP was better on some of their scopes. Some HP scopes were close to flat at their rated frequency but it's supposed to be the 3db down point. Also most 1 to 1 probes are slow. Faster probes will be 10X or more and there will be a trim cap and a test point for adjusting a square wave so that the wave form is acurate. The only safety point I can think of is the isolation. Many things (including pre-employment tests) get blown up over not isolating ground. Hope this is of some help. If the scope is isolated and the ground lead is connected to something hot the case of the scope will be hot. REMEMBER this.

05-14-2007, 09:42 AM
Well there's some truth and info in there somewhere :) as well as more info that if
used without further education could also kill you.
Just take it slow and start with low voltage circuits until you feel well informed
(not from here) and comfortable in what you're doing.
As was also mentioned, older/used equipment can be good for learning and for some
basic trouble shooting, but not necessarily for validating performance.


louped garouv
05-14-2007, 09:57 AM
I think that the units are working, but will take them to a local neighborhood tube audio tech for a look through/testing...

the unit came from the estate of a former HP & later Digital Electronics Corp engineer...

all the tubes light and a fan engages when power is applied... the trace find button works as do the intensity/focus/alignment adjustments

i'm doing some more reading now, and am finding quite a bit online...

after awhile and some reading, i'll pick up some probes and play around with it for awhile (after the unit's been blessed), then probably try to sell them to finance some tube audio DIY effort.....

hopefully i can find someone very interested in this sort of equipment...



05-14-2007, 03:49 PM
If your tech can calibrate the gear to spec, and also verify that it's still good after being powered up for several hours, (i.e. no thermal drift), have him put a calibration sticker on it. If it can't be calibrated, or won't stay that way, there'll be little value.

Using test gear that lies to you is worse than having no test gear at all, so those that use it don't generally consider "vintage" gear very desirable. That said, some of us can't justify the $ for the latest models, and settle for older stuff with enough documentation to keep it up to par ourselves. Fortuneately, sites like BAMA and others have most of the manuals needed to do so.

05-14-2007, 05:38 PM
I'm sorry grumpy, I think I may have used a scope once or twice and I've sure seen a fool or two not understand about isolation. Today's kids have battery powered units and wouldn't understand what all the fuss is about. Hook a scope up to medium voltage (one designed for it) and check out the precautions. I suppose I shouldn't offend so easy but sometimes one gets to feeling that one knows how to do so few things anymore that when they take the time to give a step by step, primarily on the safety part.(speaker terminals are sometimes a no no for scope ground leads) it's a little hard to be dismissed out of hand by someone who's credentials one has no knowledge of. There I vented. I defended myself and I don't believe I said anything offensive to or about anybody else. at least that was the intent. As far as calibration. What is necessary depends on the work you are using it for. It is important to know how accurate it is or isn't so you know what it's appropriate for and so that you don't adjust things to your scope if they are more accurate than the scope is. A lot of scopes never have the amplitude used for anything but relative readings in which case it's not important if 5 volts is really 5 volts as long as it's linear and stable. just an example. If this is a tube type scope they tend to be more popular in the winter than the summer. Someone will get that.

05-15-2007, 04:43 AM
In it's day it was one of the finest 500W heaters money could buy.

05-15-2007, 09:20 AM
Thom, it's not clear to me what prompted an apology... although I sort
of understand how you might have been offended... sorry for that.
Internet doesn't convey expression or intent very well...

I don't think anyone here questions your experience, myself included.

A dismissal of your concern and well intended info was not my point...
that there was good info as well as incomplete info (enough to get someone
killed without further training and education) was my point. It's not
possible to give a step-by-step electronics course in a single email.
High voltages and oscilloscopes (especially tube units) are not exactly
introductory material, even if isolation transformers are added to the

I -know- we both had Louped Garouv's best interest and safety in mind
so I hope we can both be happy with that. :)

In regard to cal... I would consider old/uncalibrated equipment to be useful, but
for indication only, much like an uncalibrated ohmmeter can be considered a still
useful continuity checker. You have to know how to interpret the lies :D
(understand the limitations).

gotta go.


05-15-2007, 06:39 PM
Sounds like we agree. Thank you.

05-16-2007, 04:19 AM
Yeah - no one wants to let the magic smoke out of loupie Garouvie ...
it'd be an awful shame.

louped garouv
05-16-2007, 05:16 AM
Yeah - no one wants to let the magic smoke out of loupie Garouvie ...
it'd be an awful shame.

myself included......

the tubes are so pretty tho'.......

almost can't resist.....