Wow guys this very simple device which I made up according to directions from my technician is briliant for detecting short circuits and preventing disasters such as the meltdown I had with the Hotpoint Radio in tech advice.

It consists of 3 * 60 watt globes with the first one wired ( active ) directly to the active connector on the bulb socket and active again going out of the neutral side of the socket and directly to the active side of a switchless power socket. The earth and Neutral going directly to the socket. Then the other 2 bulb sockets hooked up in parallel.

The guy showed me on my own radio how well it works by putting a dead short on the on off switch , The bulbs will glow brightly if there is a short or nothing at all if things are fine . Its absolutely brilliant ( forgive my pun lol ).

Known mostly as a dim bulb tester -- the bulb is goes dim if there is no short and remains bright if there is a short.

The total (incandescent) bulb wattage should be greater than the rated wattage of the radio under test by around 2 times.

I think you have one wired in series? (Not shown in your diagram.)

When using multiple bulbs, you can get fancy and switch them progressively in or out of circuit to vary the total wattage.

No that is actually the correct wiring diagram. The fellow who drew it up actually cut his teeth on valve radios and that is the diagram I used to build it. You only need two bulbs but I opted for three. As I said if your radio is ok then no bulbs light up ( not dim ) and if there is a short then they are bright.

Depends on inrush current of the set/equipment under test. This will vary, depending on design of the load. Some will draw significant current briefly, and then settle down to the rated wattage once valves are operating and capacitors are charged up.

Ok I have a question . He has this operating with a isolation transformer and a variac . Does it Matter which one is in the power point first or can it be any which way. I have not asked him yet but will.

The role of an isolation transformer is to remove the link to earth, which exists at the meter board where usually the neutral link is physically joined to the earth rod. The transformer therefore makes the mains on the secondary side "float" above earth so that anybody connected to earth does not complete a 240 volt circuit through their body.

The transformer ratio is 1:1, 240V in, 240V out, but you need to be aware of its current handing capacity in order not to overload it. Radios are usually light current loads, so you don't need a large transformer.

So, first comes the isolation transformer, and then other stuff such as a variac.

(I should add, that a variac, being by design an autotransformer, provides no isolation at all.)

So I am guessing that it should be isolating transformer then the Dim Bulb Tester and then the Variac because I'm assuming the Bulbs may not like the input being varied. Just putting the queery out there.

Voltage-wise, bulbs don't mind anything as long as it's not above their rated voltage. You can bring a bulb from off to full on via a variac, just like a domestic light dimmer (except that they use triacs).

Standard light globes are a purely resistive load. You can dim them pretty much any way you want. Baretters, that are used in many Australian AC/DC sets are pretty much a 60-75 watt light globe and were a cheap and reasonably reliable way of limiting current flow.

Ah of cause I did not think of the light dimmer situation now that makes things a little clearer.

The light bulb is an old trick, the poor man’s variac.
You can use it to be nice to radios by winding them up gently over 5 or 10 minutes if you want to,
and then also taking time to turn them off. Also, valve radios will happily run at a Voltage
significantly lower than mains, but each radio is too different for a figure.

I was going to bolt a pair of isolation step down formers together in reverse for a “double insurance former”,
then a variac and meters, but it didn’t make sense for the isolation formers to be present in daily use.
The radio next to me is grounded again independently (stake in the Earth) as part of it’s antenna.
Brad might know if there’s a consequence re-referencing it to ground that way, and ever touching the active.
I suspect there would be, and the isolation former defeated the purpose of the RCD.

You can’t go wrong if you buy a good nylon driver, then there’s just no reason to ever deliberately touch one live is there?