Signal Generators, Oscilloscopes, Test Sets

[Thyristor]

A basic audio lab really only needs:-

An audio oscillator / signal generator.
An oscilloscope (a proper analogue one....just get a Tek, avoid Gould/Advance, they are not worth the bother)
A dummy load.
A digital multimeter, although 2-3 can be handy, to measure multiple parameters, on first light up, say.
For radio, add an RF signal generator, say an Advance E2. (I think mine's a Taylor)
And a frequency counter can give a nice, warm fuzzy feeling!

I favour test gear from the 70s, and 80s, no software, no fiddly menus, and most importantly, manuals are usually available, so this stuff is, in itself, repairable.
Most of my stuff is 30-40 years old, and still going strong, it was built to last!
My Fluke digital meter still has an old 1982 cal sticker on the back.

Some nice stuff here for ideas (scroll down a bit)
http://www.njohnson.co.uk/

However, on watching various youtube blogs, everyone seems to need at least 130 oscillloscopes, 265 multimeters, and 87 spectrum analysers......

[tony brady]

If testing power amplifiers a THD meter/ analyser with a monitor output is also useful.
Use channel 1 on the scope for the signal output from the amp and channel 2 for the monitor output to view the THD residual. This is useful for setting up bias current as the crossover distortion can be seen on load and it's also easier to find the maximum power at the onset of clipping as the residual rises substantially

[John Caswell]

It might be worth looking out for AWA (Amalgamated Wireless Australasia) products, particularly the F242 automatic analyser, and the G233 audio oscillator - excellent products and greatly underrated - beautifully built, the only minor problem on the F242 is the meter plastic surround cracking/disintegrating but Araldite cures a lot of problems.
The Tek 500 series of test equipment is excellent but now tends to be expensive, as are the the Sound Technology products.

John

[mhennessy]

Originally Posted by tony brady

If testing power amplifiers a THD meter/ analyser with a monitor output is also useful.
Use channel 1 on the scope for the signal output from the amp and channel 2 for the monitor output to view the THD residual. This is useful for setting up bias current as the crossover distortion can be seen on load and it's also easier to find the maximum power at the onset of clipping as the residual rises substantially

Yes, and as well as watching it, listen to it! Some test sets have a built in loudspeaker for this, but many don't. With practice, you can tell a lot from the sound of the residual - the harmonics of a 1kHz sine wave fall into the most sensitive region of our hearing.

[pipeline1979]

Thanks to everybody for their opinions. For somebody just considering this as something to try in my spare time it's important to take it one step at a time, so knowing what I need most to begin with is really good. I agree that something to analyse/measure distortion is less immediately necessary and would be something I would pick up later if the right thing came along. And I would favour something simple, older and repairable. Absolutely, the first thing to understand is what I want to measure, how to do it and what it proves.
Things like putting together the dummy loads, maybe installing some cheap test speakers etc. seem like a useful place to start.
I've got an oscillator lined up if I can get it delivered. The last thing is the scope, here I'll probably just get an analog Tek or Hameg.

[Thyristor]

Despite what certain youtube blogs might have you believe, you need very little to get started.
You're certainly on the right track; an oscilloscope and an oscillator can show you so much.
You don't even really need a true RMS meter; I dare say that John Linsley-Hood, Peter Walker, Mike Albinson, Harold Leak, and Arthur Radford didn't have them, more likely an AVO8, perhaps an ancient Solartron.

Use a digital multimeter to check your DC circuit conditions and a scope for AC. For instance, by carefully looking at your output trace, you can 'see' distortion, see here:-

http://www.jacmusic.com/techcorner/S...ch102/thd.html

Learning how to interpret your results is equally as important, look out for books by Gordon J. King, I have several of his books, all are practically oriented, also 'The Audio Technician's Bench Manual' by John Earl (which is Gordon J. King by another name!)

Coming back you youtube (ugh!) W2AEW has done some excellent relevant videos (I think his videos are the best on youtube, but each to their own)

[Radio Wrangler]

You mention Arthur Radford... well he did have to develop an ultra-low distortion meter and matching oscillator and even put them out as products (I suspect they were Bailey designs)

What we don't know is what special test equipment all these people had. J L L-H certainly quoted lots of distortion figures. I suspect Leak and Walker had distortion measuring rigs and a variety of valve voltmeters, also audio wavemeters were on the go in the period.

Most probably they didn't have true RMS metering, but they would have had an interesting variety of other things. True RMS meters really only come into their own when making noise measurements.

[Diabolical Artificer]

Regarding a distortion analyser, it's possible to get an HP or Marconi cheaply if you wait and keep a look out, but as other's have said, this is one of the last bits on your list.

One thing I would advise is to put some thought into the ergonomics, the layout of your bench. For instance, my variac and lamp limiter are on the left, so I can switch the DUT (device under test) on with my left hand whilst holding a probe say in my right hand. Speakers dummy load etc in the middle, as an amplifier say or most gear has it's outputs at the back. DMM and other stuff on my right.

Your in a fortunate position as you have an empty test bench, mine has gone through several incarnations, I wish I'd had more idea when I started. It's good to stand there with an amp in front of you and go through the motions of testing it with only virtual test gear. Oh and put lots of thought into where your mains distribution is going to go. Your going to need lots of plug sockets and cable management to start with.

So, you can start by making a dummy load, a lamp limiter, a junk speaker with a switchable resistor in series and get a cheap MP3/4 player, all cheap to get or make.Oh, and don't forget the bench, make it the right height for a start, so you don't b*gger your back. Mine is high as I'm tall, and I stand to work, not sit. Also don't forget the lighting, you need good strong light to see what your doing, if like many of us with iffy sight, magnification too. One last thought, keep your bench small but compact. If you have a big bench, it will soon fill up with piles of tat. Having a small working area makes you tidy up and keep things neat. Don't forget the safety aspect too.

Lastly don't forget to have fun; get the breadboard out ( another cheap piece of test gear) and knock up a few circuits and make some noise.

Good luck, Andy.

[Radio Wrangler]

The fun part is crucial.

The audio and radio world is littered with people for whom it's stopped being fun, but they haven't been able to stop.

If you can look at something you've done and say "Er, that didn't work, did it?" and laugh at your own antics, you'll survive with your sanity intact.

David

[Brian R Pateman]

Originally Posted by Radio Wrangler

The fun part is crucial.

That is so true.

I have always worked on the principle that if you don't enjoy it then go and do something you do. I've been very lucky as I've been able to apply that to work as well as hobby.

Certainly in my working life there have been many incidents which have sent me back to the drawing board in a small cloud of smoke. That said I have colleagues who would not agree that my sanity is intact.

[G4_Pete]

One thing I allways have hanging within reach is a Steinel Master Check 1 . I use it mainly for capacitor checking and discharging it indicates and provides a discharge path plus you can take it off and then re-check in case there is some sneaky re-charging mechanism.
Pete

[Nymrod121]

Originally Posted by G4_Pete

" ... in case there is some sneaky re-charging mechanism."
Pete

Dielectric re-absorption?
Best wishes
Guy

[Skywave]

For measuring the output power from an audio amplifier, you don't necessarily need a full-blown output power meter. Assemble a resistive dummy load, the resistance value appropriate for the amp., and with a generous wattage rating, and use your oscilloscope. With the dummy load connected to the amplifier's output and the scope connected across it, slowly increase the voltage across the dummy load to the point just short of waveform clipping - as seen on the 'scope. Then using that 'scope, measure the peak-peak voltage across that load. The power dissipated is then (Vp-p)²/8R, where R is the resistance value of that dummy load.

Al.

[Radio Wrangler]

Planning what you need and what order you're going to get it is one thing, but reality has a way of getting in on the act. Things won't become available in the planned order of precedence.

Decide on what sorts of things you'll need eventually. Then familiarise yourself with which makes and models would be OK and which would be great (and which aren't worth bothering with). Armed with this preparation, you can pounce whenever anything useful pops up somewhere.

The pecking order only comes into play when you decide to pay full whack because there is something for which you have a more immediate need.

David

[John Caswell]

Hi all,
There are some 100 Watt 4R metal clad resistors on eBay at present which in a series/parallel arrangement and bolted to a large piece of Ali would make very nice 8R dummy loads of up to 400watts.

John