31-12-2020, 07:59 PM
I honestly think it's personal preference. I've never used an AVO8 professionally or at home. Growing up, I had an Altai analogue multimeter, but moved to digital as soon as I could and didn't look back (late '80s, I'd guess). I did rescue a couple of AVO8s from work, but they've remained in the attic, which is a shame in many ways, but at least they haven't been converted to a table lamp yet!
There are instances when a DMM will give a higher reading than an AVO8, and that can be confusing when comparing readings from a set to those given in the documentation, which would have been produced using an analogue meter. But that's never caused me a problem - voltage readings are pretty nominal anyway.
Some say that analogue meters are better for following a signal that is varying. Personally, I'd say that was a job for an oscilloscope. 'Scopes are cheap and readily available, so there's no reason not to have one. That wasn't the case back in the '70s, of course, and many radio workshops had to get by without one - but that was an economic decision, not an engineering one. You do occasionally meet people on forums from that era who still labour under that attitude, and that's a shame.
But then, I'm spoilt. I was given a 'scope when I was 16 or 17. It had a fault, but it was useable for many tasks. At the time, I had a Saturday job in a local shop, and the engineer there kept his brand new Hameg 'scope under a dust cover, and only brought it out when it was absolutely necessary. And because he hardly ever used it, he was quite slow at driving it. He would have fixed things much faster if he went to it sooner, and used it more often. Back in those days, my 'scope was on all the time I was in my workshop - it helped to keep it warm! I often used it instead of a multimeter, as for most things, precision and accuracy is not important, but seeing what was happening was. A multimeter won't tell you if there's noise or ripple on a supply rail, even if it will tell you the average DC voltage to 3 or 4 decimal places!
Another example - if you're in any doubt about that AGC cap, stick the 'scope across it. Assuming that one end of the cap is returned to earth (that's usually the case), then if you see any trace of an audio signal on the top of the cap, that tells you the cap is bad. No fancy ESR meter needed! I have a Peak Atlas ESR meter, but hardly ever need to use it because I'm so used to diagnosing bad caps from circuit behaviour. It's useful to confirm that a suspect cap really is bad, but I hardly ever use it as a diagnosis tool. I know I'm at risk of being like my former colleague who'd never use his 'scope, but it's actually quicker for me to just probe around a circuit with a 'scope than it is to measure caps with an ESR meter. But if I had less electronics knowledge, then I'd need to rely on an ESR meter rather more.
All that said, for vintage transistor radios, it's leakage that stops things working. Or caps drying out to the extent that they've lost capacitance. ESR is rarely a factor (and ESR starts to rise long before the cap is bad enough to fall in value) - when you look at the circuitry of a transistor radio, you can see that low ESR is not a requirement of most caps. But an ESR meter is really handy when fixing switched-mode power supplies - which is what the vast majority of modern repair work consists of. Before switched-mode power supplies, hardly anyone was even aware of ESR.
There are instances when a DMM will give a higher reading than an AVO8, and that can be confusing when comparing readings from a set to those given in the documentation, which would have been produced using an analogue meter. But that's never caused me a problem - voltage readings are pretty nominal anyway.
Some say that analogue meters are better for following a signal that is varying. Personally, I'd say that was a job for an oscilloscope. 'Scopes are cheap and readily available, so there's no reason not to have one. That wasn't the case back in the '70s, of course, and many radio workshops had to get by without one - but that was an economic decision, not an engineering one. You do occasionally meet people on forums from that era who still labour under that attitude, and that's a shame.
But then, I'm spoilt. I was given a 'scope when I was 16 or 17. It had a fault, but it was useable for many tasks. At the time, I had a Saturday job in a local shop, and the engineer there kept his brand new Hameg 'scope under a dust cover, and only brought it out when it was absolutely necessary. And because he hardly ever used it, he was quite slow at driving it. He would have fixed things much faster if he went to it sooner, and used it more often. Back in those days, my 'scope was on all the time I was in my workshop - it helped to keep it warm! I often used it instead of a multimeter, as for most things, precision and accuracy is not important, but seeing what was happening was. A multimeter won't tell you if there's noise or ripple on a supply rail, even if it will tell you the average DC voltage to 3 or 4 decimal places!
Another example - if you're in any doubt about that AGC cap, stick the 'scope across it. Assuming that one end of the cap is returned to earth (that's usually the case), then if you see any trace of an audio signal on the top of the cap, that tells you the cap is bad. No fancy ESR meter needed! I have a Peak Atlas ESR meter, but hardly ever need to use it because I'm so used to diagnosing bad caps from circuit behaviour. It's useful to confirm that a suspect cap really is bad, but I hardly ever use it as a diagnosis tool. I know I'm at risk of being like my former colleague who'd never use his 'scope, but it's actually quicker for me to just probe around a circuit with a 'scope than it is to measure caps with an ESR meter. But if I had less electronics knowledge, then I'd need to rely on an ESR meter rather more.
All that said, for vintage transistor radios, it's leakage that stops things working. Or caps drying out to the extent that they've lost capacitance. ESR is rarely a factor (and ESR starts to rise long before the cap is bad enough to fall in value) - when you look at the circuitry of a transistor radio, you can see that low ESR is not a requirement of most caps. But an ESR meter is really handy when fixing switched-mode power supplies - which is what the vast majority of modern repair work consists of. Before switched-mode power supplies, hardly anyone was even aware of ESR.
