Roberts R66

[LyntonP]

Didn't realise you had a variac. Excellent idea.

All the gear, no idea!
Lynton

[ppppenguin]

Didn't realise you had a variac. Excellent idea.

All the gear, no idea!
Lynton

But when quoting please put your own contribution OUTSIDE the quote box.

[LyntonP]

Didn't realise you had a variac. Excellent idea.

All the gear, no idea!
Lynton

But when quoting please put your own contribution OUTSIDE the quote box.

Like this?

[LyntonP]

I'm assuming you are using a modern electronic meter and not an old analogue meter which is badly out of calibration?

Unfortunately not Terry. All I have is dmm which is probably 20 years old, and an AVO 8 which was being thrown out at work a number of years ago. Probably a good time to invest in a new multimeter, but that will have to wait until the next pension day!
Lynton

[Refugee]

If you have got a good 15 volt battery in the AVO go for the rectifier with it on high ohms range.
With readings between all the terminals both ways it will tell us all what the diode arrangement is in the rectifier package.

[Old Sparky]

An AVO 8 in G.W.O is a perfectly good, if somewhat bulky & heavy, multimeter. All you have to remember is that on DC voltage ranges it's resistance is 20000 ohms per volt, which means that it loads the circuit under test more than a DMM, or, for that matter, a Valve Voltmeter, does. This means that the voltage read on an AVO (or any other Analog meter for that matter) will be lower than that shown on a DMM, most of which have i/p resistances of at least 10 Megohms. The readings published in the service data for your R66 were probably taken with an AVO 8 in any case - they may even have used an AVO 7 for this purpose back then, and, IIRC, the i/p resistance of the 7 on DC ranges was only 1000 ohms per volt. Besides all the foregoing, I'm temped to say 'what's wrong with a 20-year old DMM if it's in good working order. Until it developed a not-easily repairable fault, I was using a Fluke 77 which would have been getting on for that age when it failed.

[ppppenguin]

The readings published in the service data for your R66 were probably taken with an AVO 8 in any case - they may even have used an AVO 7 for this purpose back then.....

Definitely not. Unusually for a set of that period, the voltage readings were taken with an Avo Electronic Testmeter. This has a high input impedance. A modern DMM with 10M input impedance is a sensible alternative. Won't make any difference to the filament voltage measurements as the impedances are low.

A cheap DMM is all you need. Under £10 from many suppliers. For example: https://www.screwfix.com/p/lap-mas830b-d...600v/75337

[Terry]

The only trouble I've ever experienced with an AVO 8, assuming no mechanical damage, is reading low on AC. Where I first worked, all of our AVOs developed this problem one by one and were sent back to AVO for repair/recalibration.

I've got one of those Screwfix meters because, when we weere in the process of moving, my trusty 20+ year old true RMS Wavetek DMM was still in the old house and I needed one here.

Mark Hennessy has done an intensive review of £10 DMMs in this thread, which is worth looking at.

There is no reason that your old DMM shouldn't be up to the job but, if you do want to get up to date, you might be interested in this one.

You won't get it instantly like the Screwfix model but, when I bought one recently, it didn't take long to arrive.

Here it is, if you are interested.

I must admit that I was lucky as it was on special offer at the beginning of January and I got mine for just over £10 including delivery!

[LyntonP]

A cheap DMM is all you need. Under £10 from many suppliers. For example: https://www.screwfix.com/p/lap-mas830b-d...600v/75337

By coincidence I have a gift card for Screwfix. They do another meter for around £30.00. Would this be significantly better?
 Ideally I would like to check capacitance as well.
Cricklewood electronics do a meter for around £12.00 been considering one but not sure of quality?
Lynton

[Terry]

They do another meter for around £30.00. Would this be significantly better?

I was interested in these comments from a customer: "Useful little meter for general electrical installation and test work. It is not ideal for electronic testing and setting as the resolution is quite poor @ just 10mV. You couldn't set a DC bias voltage to say 2.5mV. It just reads 0.000.

Another small gripe: Unless you have 20/20 vision, some display symbols are too small to see clearly. "

This meter from Banggood is very similar to the AN8002 but includes capacitance readings too. It's discounted during February so it is actually a few coppers cheaper than the AN8002!

Capacitance ranges are from 10nF to 10,000µF [1] - resolution on the lowest range is 1pF.

[1] Actually quoted as 9.999nF to 9.999mF but I've simplified it. Similarly, the highest resolution is stated as 0.001nF!