Golborne Vintage Radio

This circuit perhaps isn't strictly 'Home-Brew' as I certainly didn't design it. I don't know who did as I found the circuit in an electronics lab when I was at college. This was a photo-stat of a photo-stat... so I've re-drawn it.

It has far more uses than the usual testing of fuses &c and even gives a pretty good guide to the state of capacitors.

There's no need to get hung up on the speaker impedance as over the years I've used everything from 8Ω to piezo transducers.

Mine has got an 80Ω one along with a socket so I can use this a high (ish) impedance test speaker. I've also added another one so I can use the tester's output as a crude signal generator.

Basically the higher the tone it makes the lower the resistance it's testing. Very high resistances will produce a series of pips and it's surprising how it can be pipping every couple of seconds on things that other meters have read as infinity.

I've had one for twenty-five years now (Tempus Fugit and all that) and found it immensely useful. There's an audible continuity tester on my DMM but I don't like it because it's too quiet and... well... digital in that it either bleeps or not.

I hope other people find it of use.

Joe

I like that Joe - think I'll knock one up tonight since TV is, as usual, boring rubbish. Trying to think of something to show/tell about myself.

Colin

Thanks, Colin; it's only taken the best part of three years for somebody to reply to this thread!

Since then I've added another 555 so it can also be used as a dedicated signal injector.

A also made another continuity tester with an LED and a couple of 2N2222s to keep in my jacket pocket. It's not as good as 'Old Faithful' though.

http://www.youtube.com/watch?v=l5eZ69JrL14

- Joe

It's only taken the best part of thirty years but I've finally designed a PCB for this:-

[attachment=12723][attachment=12724]

- Joe

That's a useful idea. I have a different continuity tester that's handy when there are multiple circuits to be identified. One end is a 9V battery and bleeper. It can be used as an ordinary tester. The other end is the magic bit. I forget the circuit so would need to open it up but it's basically a bridge rectifier, capacitor and a couple of other bits. When connected to the tester it warbles instead of bleeps, hence showing that you're connected to the same pair of wires at each end. Because of my video background the connectors are BNC on each unit. Hence BNC to croc clip leads are needed for other purposes.