Light Bulb Tester

[Speedskater]

A "Light Bulb Tester" is often suggested when testing a new or modified circuit. But it often takes much searching to find the tester. So below is a schematic and photos. I built the tester out of spare parts. I'll let others clarify using the tester.

[Speedskater]

Also see this thread for links and information:

mains light bulb tester.

[Speedskater]

The need for a tester just came up in another thread.
So I thought that this needed a bump.

[wwenze]

Can we have a "Show your light bulb tester photos" thread?

[Enzo]

Google "light bulb limiter" instead of "tester."

[Speedskater]

In another thread simon7000 wrote this about using a light bulb tester to repair a solid-state amplifier:

No, but you can usually repair it without one (a manual).

I don't know your level of expertise so I will outline the entire fix it blind procedure for a solid state audio power amplifier built with discrete semiconductors.

It has a linear power supply, so you don't need to start there.

You will need to build a light bulb box to test your work as you go. This should be a 40W or so light bulb in series with the ac power line.

The next step is to make sure all the fuses are good and then power up the speaker through the light bulb.

The bulb should flash bright when it is first powered up, then settle to a dim glow.

If it stays bright then remove all of the output transistors and check then for dead shorts. If they are good reinstall them and check the driver transistors. After you replace the bad transistor(s) you can try powering it up again. If that doesn't do it it you should check the input transistors again for short or open.

To test the transistors all you need is an ohm meter. You will need to do all six possible connections. All the good transistors will measure the same as their like types (NPN or PNP) the bad output transistors normally show a dead short, inputs often will have an open lead.

If all the outputs, drivers and inputs are good, but it still isn't right, replace the current sources to the input stage.

Most likely is one bad output transistor. If the unit has a protection relay the light bulb will flash and go dim but the relay will not close. Repair is the same.

[DF96]

Also known as a 'lamp limiter'. In addition to the on/off switch, it can be useful to add a switch to bypass (i.e. short out) the lamp. Only use this when you are confident that the equipment being tested works OK.

[AndrewT]

Originally Posted by DF96

Also known as a 'lamp limiter'. In addition to the on/off switch, it can be useful to add a switch to bypass (i.e. short out) the lamp. Only use this when you are confident that the equipment being tested works OK.

yes, this is shown in Decibel Dungeon.

But, I think the switch must be push and hold to make. Otherwise it could accidentally be left ON, defeating the tester.

Very useful addition if it can be made foolproof. I have never added either switch, because I know I will forget. I do realise the switches make the tester much more usable, I'll just need to find a suitable switch.

[simon7000]

You guys really need to subscribe to AudioXpress. I have shown this two or three times.

[6L6]

I made mine from an IEC cord and a simple socket from a broken Ikea lamp --


It may not be pretty, but it works!


It is wired like the example in Decibel Dungeon -