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Quick lightbulb test jig

gonzothegreat

gonzothegreat

Super Member
For years I've used a variac to power up suspect equipment but I've always meant to build a lightbulb jig.

For those of you in the dark about the lightbulb trick, here are the details. Put a 60W (or more) lightbulb in series with whatever gear you are testing. If it tries to draw too much current, the bulb will glow brightly and keep things from going KA-BLOOIE. The gear may not work 100% as it isn't getting full voltage.

Over at the local home improvement store (Menards) I decided to grab the parts needed to cobble one together. I discovered that building one is a five minute job with only four parts.

Parts required for light bulb jig

Two wire extension cord (preferably polarized but NPO is OK)
Westinghouse "Make-a-Lamp" kit (roughly $6)
Light bulb
Wire nut

Cut plug off extension cord and strip both wires. Screw one wire to lamp socket from kit. Screw one lead from lamp kit's cord to other lamp terminal. Wire nut the remaining leads together. Assemble lamp socket and screw in bulb. Mission accomplished!

Plug the gear into the outlet and plug everything in. When you turn on the gear, the light should briefly glow brightly then grow dim.

Considering this doesn't even require a soldering iron, *nobody* has any excuse not to have one of these.

IMPORTANT NOTE!!! REALLY IMPORTANT!!! I MEAN IT!!! YOU'LL BE SORRY IF YOU DON'T READ THIS!!!

If you are testing a VFET amp like the YAMAHA B-2 or the Sony VFET line, do not use this test device. You could possibly fry the VFETs and you'll be left with a large boat anchor full of shorted silicon.
 
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You are correct sir!

The other handy gizmo to buy/build if you don't have one AND if you do any work on transformerless circuitry (e.g., "All American Five" tube AM radios) is an isolation transformer.
 
Screw that stuff..............I just toss the set into a filled bathtub and determine by how much it sparks if the caps are good or shorted.


Why is it you guys always chose to do things the hard way?

Anthony
 
Originally posted by heathkit tv
Screw that stuff..............I just toss the set into a filled bathtub and determine by how much it sparks if the caps are good or shorted.

Why is it you guys always chose to do things the hard way?
Click to expand...

Well, the last time I did what you suggested, my roomate was shaving her legs and she wasn't too happy with the new bath toy.
 
When a fuse is blown in a piece of equipment, we always get out the series light bulb short checker at our shop. We replace the fuse and then put the device on the short checker until we have found the fault...it is great for troubleshooting shorts in transistorized stereo receivers as well as checking out tube type devices. I use a 60 w. light bulb.
 
I built one a couple of nights ago to check my thrift store Pioneer SX2000 out. I used leftover junk in my garage. It took 2 Electrical box's, a GFIC outlet. a switch, a duplex outlet some stripped romex, a salvaged 3 prong power cord, the appropriate covers, and an old bulb socket that plugs into a duplex for temp lighting.

I used a single box for the GFIC and wired the power cord into its line posts. I joined the 2 box's with a short conduit run and ran the romex wires from the GFIC load posts to the other double box.

EDIT: I should have mentioned this: Be sure to wire the black wire to the Gold side and the White wires to the “white” or silver screws. This keeps the hot and the common polarized properly.

The black went to the Switch, the switch went to the gold side of the duplex outlet. I removed the snap out bridge on the gold side so the 2 outlets were isolated on the GOLD SIDE ONLY. I wired the white wire to the “white side of the duplex. Mounted both switch and duplex to the metal cover and screwed it down.

I marked the “input” duplex as LAMP and circled it with magic marker. Plugged the lamp socket into that outlet and marked the final outlet LOAD.

Now I have 3 usable outlets. All protected with GFIC. The 2 GFIC outlets are house current and useable for anything. Gear, test equipment the unit your working on. If it is shorted, or just wired dangerously, the GFIC will tell you, instantly! The load outlet gets whatever you use for a load in the bulb socket as a limiter. The switch allows me to control the output load directly.

Worked great! And has an extra layer of protection with the GFIC.

I’ll try to post/host a pic.




loadtester.JPG
 
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The other handy gizmo to buy/build if you don't have one AND if you do any work on transformerless circuitry (e.g., "All American Five" tube AM radios) is an isolation transformer.
Click to expand...

What is an Isolation Transformer? :dunno:
 
Light bulb thing

I use a 60-100watt bulb depending on the amps power. . . Any amp that I dont know and know it has been sitting a long time I soft start it with my light bulb thing. . .

BTW be sure your speakers are not connected especially with Adcoms. . . they go into oscillation or something, make a funny noise that I never heard before. . .

I can tell if a 850/1050 Pioneer is biased corectly as I have checked so many. When you first turn it on the bulb shines bright as the caps charge then the light dims to a soft orange if the bias is set right. If the light goes out completly bias is too low. . . On a 1050 Pioneer anyway. . .
 
Isolating the equipment from the source helps reduce
shock hazzard or damage to the equipment if the unit
being tested has a fault.
 
OK, thanks.

Wouldnt a GFIC do as much or more? any issues and the power is cut, now!

or is it also to limit spikes and other variations? Wouldn't those get pumped over also, or are they smoothed out by the transformer?
 
All a GFIC does is cut power if the current through the neutral does not equal the current through the hot.

Just like glen65 says...a transformer gets you one step away from being directly plugged into the AC mains.
 
Isolation transformers eliminate the hazard of being shocked by a "hot chassis" set. AC/DC tube radios and TV's had one side of the power line connected to the set's ground. If you had the plug plugged in so that the chassis got connected to the "hot" instead of the neutral and you touched the chassis, you got a shock. Using an isolation transformer insulates the otherwise "hot" chassis and allows you to work on the set safely. Most current TV sets are also "hot chassis" sets, incidentally...saves having to use an expensive power transformer.

TP
 
Since we're tossing around a few different terms, let me try to clear things up.

A variac just varies the line voltage. Variable AC. Mostly good for slowly bringing old gear up to full voltage so the caps have the chance to reform and not pop like a zit. Some variacs have isolation transformers built in but most don't.

The lightbulb jig just limits current to the device under test. If something is shorted, the bulb will glow brightly. The shorted DUT (low resistance tries to draw high current) causes the majority of line voltage to be dropped across the lamp. The added resistance of the lamp limits current.

An isolation transformer passes line voltage through a high power 1:1 turns ratio transformer. This keeps you from zapping yourself when working on hot chassis TVs and tube gear. Not really needed if you only work on solid state stereos. Please note that an autotransformer may *look* like an isolation transformer, but it doesn't isolate.
 
Great thread for DIY...

When I'm working in the shed I just tell the kids to come check on me if the lights in the house dim or flicker. They actually did once when I welded my screwdriver to a chassis...

I think this is a great thread. I am definately going to build a jig before I try to power up my current project :thmbsp: .

Thanks for the insight,

griz780
 
Interesting this came up again today. I had to work on the heater this evening to figure out why it wasn't going. there was a CB on the main panel and a switch woth a funny lookin box on it. no power was getting to the heater. I pulled on the box and whaddaya know, its a single hole fuse box. Power at the center of the fuse hole, but none to the heater. Fuse looked good. Hmmm, Ohms meter test and bingo, the fuse (regardless of appearance) is blown.

What does this have to do with this thread? When I went to get fuses, (Yes I bought spares...) in the same rack are more of these little one hole fuse boxes. Several styles, but either switched or with a duplex outlet were available. Tear off the little box cover over the fuse and you have a perfect unit to make the light bulb test jig. They ran about $7... All you need do is decide switched or duplex and get a box to mount it. a couple of romex clamps and scrounge a grounded cord with a plug on it...

I'm done, but for those planning one :naughty:
 
OK, for those that don't want to spring for a variac, (I bought a small 3A one, but its not built into a box as yet...) I have been reforming the caps in a Motorola tube amp, and used my Dim Bulb Tester to do it.

I also did some documentation on actual voltages achived with various bulbs, and there measured resistance just for grins.

Keep in mind. all this tester cost me was a 240 watt bulb, since I didn't have one of those laying around. All else I already had...

Dim bulb tester - Bulb ratings and results.

Load Motorola Mono Tube amp, .62A @ 117VAC (72W)

bulb wattage - ohms resistance - resulting Voltage @121VAC

40 - 26 - 67
60 - 19 - 81
100 - 10 - 91
150 - 7.5 - 100
240 - 5 - 110

The collums spacing may suffer, But you get the idea...

I'm not certain what kinds of resistance tolerances lightbulbs carry, so your mileage may vary...
 
tester

Outlawmws, That makes a dandy refrigeration compressor starter too, if you are in to that. The bulb does the job of the relay!

Steve
 
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