Compact Dim Bulb Tester Wiring

OverLoad

High On Solder Fumes
I was asked in this thread about the wiring and to show the inside of my DBT. So for tsd71 and other's benefit wanting to build my compact DBT version, I'll discuss it here. Pictured below is the DBT in question followed by the schematic. Also pictured is a quick mock-up I made rather than pulling mine apart so you can physically see how it's all connected. In the pictured mock-up, the black wire is the "hot" path, the white is "neutral" (depicted blue in the schematic) and the green/bare wire is ground. The longer slots on the outlet are the neutral side. In this case the 3 prong plug and cord are standard black, white and green colour coded. I've seen other cord colour coding such as brown, blue and yellow for example. Regardless, it is easy to determine with a continuity check what wires are hot, neutral and ground by knowing the longer slot of an outlet is neutral, the other slot is hot, the middle is ground and that a 3 prong plug can only be inserted the one way.

The hot wire of the plug-in cord goes to the bottom screw of the switch (off position). A wire form the top screw of the switch (on position) goes to the hot side of the top outlet (which has been isolated from the bottom outlet by breaking the tab). A wire from the neutral side of the top outlet (which has been isolated from the bottom outlet by breaking the tab) goes to the hot side of the bottom outlet. The neutral wire of the plug-in cord goes to the neutral side of the bottom plug-in. The ground wire of the plug-in cord ties to the outlet ground screw and the metal electrical box if applicable. The top outlet is where you insert the plug-in socket lamp and the bottom outlet is for your device under test.

The schematic and pictured mock-up obviously don't show the 2 gang metal electrical box that houses the duplex outlet and switch. If you use a metal electrical box as I have, then make sure the box gets grounded as well.




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DBT_Sch.jpg

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I've seen people building these using only a 2 prong plug and worse yet, without polarization :nono:
It's of course fine if your electrical is the older 2 wire outlets (use a polarized plug if you can) but if your electrical is present day Canadian and American code then I can't stress enough that a 3 prong grounded plug and cord be used with grounding and proper polarity strictly followed. In simplicity the DBT is an extension of the wall outlet mains but with a bulb in series on the hot side so wire it PROPERLY and SAFE! :thmbsp:
 
Yeah, thanks. I've got a refurb of a Marantz 2240B in my future so I'll be building one. What wattage bulb did you use?
 
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......What wattage bulb did you use?
I have 4 plug-in socket bulbs each with a 40W, 60W, 100W and 150W bulb for quick changing of the desired wattage I need. The required bulb wattage really depends on the device under test. The smaller the bulb wattage, the more the current will be choked and mains voltage will be reduced. For example, a large power amp that is functioning perfectly may exibit a false bright bulb and may or may not come out of protection on a 60W bulb because of being "choked" too much.

A good rule of thumb is 40 to 60 watt bulbs for small items such as CDPs, tuners etc. For large power amps, usually a 100W bulb is sufficient but rarely do I require more than the 150W.
 
must do a diagram for uk if someone doesn't beat me to it .. we use different coloured wires .plus we have live neutral and earth ..no such thing as a plug in lamp bulb ..
live /hot. brown
neutral/cold. blue
earth green yellow ..
old code was black neutral ..red live ..green earth .. much better but some idiot decided blue brown green yellow was better
 
I was asked in this thread about the wiring and to show the inside of my DBT. So for tsd71 and other's benefit wanting to build my compact DBT version, I'll discuss it here. Pictured below is the DBT in question followed by the schematic. Also pictured is a quick mock-up I made rather than pulling mine apart so you can physically see how it's all connected. In the pictured mock-up, the black wire is the "hot" path, the white is "neutral" (depicted blue in the schematic) and the green/bare wire is ground. The longer slots on the outlet are the neutral side. In this case the 3 prong plug and cord are standard black, white and green colour coded. I've seen other cord colour coding such as brown, blue and yellow for example. Regardless, it is easy to determine with a continuity check what wires are hot, neutral and ground by knowing the longer slot of an outlet is neutral, the other slot is hot, the middle is ground and that a 3 prong plug can only be inserted the one way.

The hot wire of the plug-in cord goes to the bottom screw of the switch (off position). A wire form the top screw of the switch (on position) goes to the hot side of the top outlet (which has been isolated from the bottom outlet by breaking the tab). A wire from the neutral side of the top outlet (which has been isolated from the bottom outlet by breaking the tab) goes to the hot side of the bottom outlet. The neutral wire of the plug-in cord goes to the neutral side of the bottom plug-in. The ground wire of the plug-in cord ties to the outlet ground screw and the metal electrical box if applicable. The top outlet is where you insert the plug-in socket lamp and the bottom outlet is for your device under test.

The schematic and pictured mock-up obviously don't show the 2 gang metal electrical box that houses the duplex outlet and switch. If you use a metal electrical box as I have, then make sure the box gets grounded as well.




002.jpg


DBT_Sch.jpg

001.jpg


002.jpg


004.jpg


005.jpg


006.jpg







I've seen people building these using only a 2 prong plug and worse yet, without polarization :nono:
It's of course fine if your electrical is the older 2 wire outlets (use a polarized plug if you can) but if your electrical is present day Canadian and American code then I can't stress enough that a 3 prong grounded plug and cord be used with grounding and proper polarity strictly followed. In simplicity the DBT is an extension of the wall outlet mains but with a bulb in series on the hot side so wire it PROPERLY and SAFE! :thmbsp:

Absolutely the best Dim Bulb Tester thread ever, great pics, great explanation. I'm sure many DBT's will be built using this thread. I love the compact size....THANKS!:thmbsp:
 
Jon,

I prefer having the switch acting as a power switch because there are quite a number of instances where a power amp for example, doesn't have it's own power switch. I can quickly remove power this way rather than having to pull the plug. I originally built a 3 gang box that included both the power switch and a switch to short the bulb for full mains. I chose to resort to a 2 gang box and remove the bypass switch for two reasons:

1. I didn't like the fact that full mains could so easily be switched on, accidentally or not. If you'll notice I have a shorting plug attached to the front with velcro. Simply pull the socket bulb and insert the shorting plug. This is almost as quick and easy as flipping a switch but you obviously have to be very purposeful about it which I like.

2. The DBT is now even more compact which was my original goal.

You can build it with power switch as is, substitute the power switch and wire it to short the bulb for a full mains switching option or go the 3 gang route and have both. It doesn't stop there either as there other builds and options with things you can add. I'll leave it to the individual builders on how they wish to construct their DBT's.
 
Hi OverLoad, thanks for the reply.

I understand. There's no one right way for these. It's how you want to use it.
 
Bulb Wattage per Wattage amp.

I was wondering if there is a formula for calculating the bulb wattage required per watt of the amplifier. i am in a position where I need to test a 300 watt tube amplifier, and want to run a couple bulbs in series. Any recommendations or comments? Thanks!
 
You don't do a power test (ie 300W max power, etc) with a DBT in-line.

The DBT is just there to bring up equipment that is in an unknown state. The wattage of the bulb will depend on the amount of current consumption at idle. There is no magic rule about a product and the bulb needed.

A 75W bulb will probably allow most small things, such as a tuner, pre-amp, or CD player to get most of the voltage. You might need 100W, 150W, or 200W bulbs to get most of the line voltage to drop across your DUT, if it is a power amp.
 
I have a DBT, but am mulling a design for a new one. My plan is 2 or 3 bulbs in sockets, each on a switch so that adding wattage is as easy as a switch. There are 2-in-1 and 3-in-1 switches that should do that nicely... and another switch for bypassing the bulbs. After this thread, I might put it under a safety cover, one that you'd usually use for covering a switch or plug outside.

I also plan to put in another outlet on a switch for my "hot" tools... so that turning off the heat is as easy as a switch... no more plugging / unplugging the 808.

One of these days...
 
I also plan to put in another outlet on a switch for my "hot" tools... so that turning off the heat is as easy as a switch... no more plugging / unplugging the 808.

One of these days...

I have all my test equipment and soldering gear plugged into a heavy-duty switched plug strip. One flip and it all goes off.

Tom
 
Mine's the same ... only different.

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Handy little devil to have laying about.

* Don't forget to stock up on some spare bulbs. Not sure if these will work with CFLs.
 
Great thread.

I just made a parts list and will build one.

*Update*
Just finished building mine - works great!
 
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