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Old 27th May 2010, 05:20 PM   #1
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Default Light Bulb Tester

Rangefinder writes that "Dim Bulb Tester" is more historically accurate. see post #38

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.
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File Type: jpg TesterSchematic.jpg (43.2 KB, 1331 views)
File Type: jpg Tester2sm.JPG (83.1 KB, 1310 views)
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Last edited by Speedskater; 16th November 2012 at 12:34 AM. Reason: added "Dim Bulb Tester"
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Old 27th May 2010, 05:27 PM   #2
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Also see this thread for links and information:

mains light bulb tester.
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Old 26th March 2011, 06:38 PM   #3
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The need for a tester just came up in another thread.
So I thought that this needed a bump.
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Old 27th March 2011, 04:05 AM   #4
wwenze is offline wwenze  Singapore
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Can we have a "Show your light bulb tester photos" thread?
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Old 27th March 2011, 04:35 AM   #5
Enzo is online now Enzo  United States
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Google "light bulb limiter" instead of "tester."
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Old 27th March 2011, 05:27 PM   #6
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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.
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Old 28th March 2011, 12:25 PM   #7
DF96 is offline DF96  England
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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.
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Old 28th March 2011, 12:47 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by DF96 View Post
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.
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Old 28th March 2011, 01:57 PM   #9
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You guys really need to subscribe to AudioXpress. I have shown this two or three times.
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Old 28th March 2011, 02:11 PM   #10
6L6 is online now 6L6  United States
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I made mine from an IEC cord and a simple socket from a broken Ikea lamp --

Click the image to open in full size.
It may not be pretty, but it works!


It is wired like the example in Decibel Dungeon -

Click the image to open in full size.
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