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Cold Cathode Tube Voltage and Speaker Questions Answered

My brother has some cold cathode tubes, some about 6" long, some about 12" or more. I was thinking of hooking them up to my bike, as shown in one of the great Instructables here, but I wasn't sure of the voltage. I don't want to over-power the tube, and bust it. Plus, the two wires coming out of it are in this black connector, so I don't know which is positive or negative. The tubes put out blue light, if that makes any difference.

I have an old sports radio, which works pretty good and could be turned up really loud. I desoldered the speaker, and hooked it up to a pair of wires coming from a head phone jack. I plugged it into my iPod, expecting loudness, but no - I had to hold it up to my ear, on full volume, to hear it. Is it because the iPod isn't outputting as much voltage or current to the speaker as my radio was? The radio used 3 AA. I really wanted a portable speaker that actually put out big sound, so I didn't have to have those buds stuck in my ear.

Thanks y'all!


concerning the speakers, it sounds like you have a very mismatched "impedance". If you can find out the output impedance of you iPod, the speaker "should" have its rating on the back metal guard around the permanent magnet (should say something like 4Ώ , 8 Ώ, 16Ώ etc. )

The speaker says 8 ohms and .5 Watts.

. I'm with Goodhart. I think your speaker impedance is too high.

Adding to my other comment about giving it more power, I happen to have a pair of computer speakers. I currently use them in my room to play my music, but they have to be hooked up to a wall. Do you think (and how could I do it) I could run them off of DC power, i.e., batteries? If you need a picture, I can take one. I've looked in the main speaker, and it has a pretty big transformer. I don't know what this brings the needed voltage and current down to, though. THanks for your time.

> Do you think (and how could I do it) I could run them off of DC power, i.e., batteries? . Should be able to run them off of batteries. Check the output of the wall wart for voltage and ampacity. If there is a transformer in the speaker, the wall wart may be putting out AC and the rectifier is in the speaker. . If you have a sub-woofer, the "transformer" may be part of the cross-over network. . If you don't have a wall wart (speaker plugs directly into wall), you will need to ID the rectifier/filter output points.

It has a standard plug; a 2 prong, small plug. No adapter there. The transformer is inside the speaker. The only voltage I saw said 110v, which I'm sure is input from the wall. I don't have a woofer, they are just two small speakers. One thing I've noticed is that the speaker in the main box has a round metal cap on the back end. It stands out because it's silver-metal colored, not the yellow-ish color as usual. I don't know what that is, and it doesn't have any markings on it. Again, thanks.

. The 120V will go to one side of the transformer. The other side of the transformer will go to a rectifier and possibly a filter. Try using a voltmeter to locate the rectifier/filter output (probably be between 5V and 15V DC). You should be able to hook up your batteries there.

Ok, I think I see where you're going with this, and this is going to sound really newbie-ish, but what does a rectifier look like? I took pictures of pretty much all there is to this speaker that I can't explain, so maybe it's there, I just can't see it. Thanks, yet again. ;-)

Speakers 013.jpgSpeakers 012.jpgSpeakers 010.jpg

. I don't see anything that is obviously the bridge. I think the IC is the amp, but not sure, it may be the bridge.
. Check the labels. Cx = capacitors, Rx = resistors, VRx = variable resistor, Jx = jumper, etc. IIRC, Dx = diodes.
. Where do the different wires go? I can't tell which is 120VAC (top right?), speakers, etc. The red/black pair looks promising - common color combo for DC.
. Diodes come in several forms. Most I've seen in similar applications are tubular with axial leads - like the resistors in your pics. Some are clear glass (usually very small), some are black with a silver band (or cone-shaped) on one end.
. Four diodes to make a rectifier bridge. Sometimes they are packaged in one small IC.
. Do you have a VOM (volt-ohm-milliammeter)? If not, you can pick up a "cheap but good enough" one for $5-10 at most auto parts stores, electronics stores, Wal-Mart, etc.

Labels - I looked at all of them, and here's ones that you didn't mention - LDx, which is just a green "power is on" LED; Ax, which are holes, bigger than ones wires would go through, and there is nothing in them. Some have a small amount of solder around the edges on the bottom of the board, but that's it. In the last picture above, in the south eastern region of the board, right below the two capacitors, you can see one, A12. Under the transformer it says SP-1700, which might be a number. The wires - If you are looking at the middle picture, you are right on the wall cord; the red/black pair lead to the speaker which is housed in the main box. The southwestern wire leads to the auxiliary jack. The southeastern pair leads to the other speaker. Diodes - I have the black w/ silver band type. Wouldn't you know it - 4 diodes together. Yes, I have a cheap meter which measures volts (AC and DC) and amps. It has an Ohm symbol on it, though I do not know if it measures them (seems as if it would, though.) Thanks yet again.

> Wouldn't you know it - 4 diodes together. . OK. The four diodes will probably be hooked end to end, in a rectangle. Two of the "opposite corners" will be the AC in and the other two will be the DC out. If they are wired standing up, then you will have do do some investigating to figure out where the corners are. . Turn everything on. Put your meter on AC volts with the range at 120V or greater. Try any two opposite corners. If you read ~110VAC, that's the input. Check until you get two corners with ~110VAC - don't use these. Verify the DC voltage on the non-AC corners (15V range should work). If you have an analog meter (needle), try to make sure you have the polarity right or you can bend the needle. . Hook up your battery (observe polarity) with a switch to the DC points you found. . Say a prayer and turn the switch on.

Thank you so, so much. I haven't had a chance to do it yet, with school and football, but this weekend will hopefully be fruitful. I will definitely be posting back soon. Thanks again!

> the speaker in the main box has a round metal cap on the back end. It stands out because it's silver-metal colored, not the yellow-ish color as usual. I don't know what that is, and it doesn't have any markings on it. . I'm guessing that it is a magnetic shield (for your monitor) and that you're missing the one for the other speaker.

OK, just making sure it wasn't something having to do with this. Oh, and the other speaker has one, just missed it.

So, is there anyway I could fix that, like perhaps give the speaker more power?

Looks like the symbols didn't make it through....after each number should be an "ohm" (Omega) symbol. 4Ω 8Ω 16Ω


10 years ago

CCFL tubes take like 1000VAC (at least as a starting voltage), and therefore need a special "inverter" to drive them. The only voltage you have to worry about is what the inverter is designed to take. Unfortunately, the surplus supply of cheap 5V inverters seems to have dried up, and it looks like the cheapest way to get an inverter these days is as part of a CCFL car or case-mod kit. Those will usually run off 12V. On the bright side, if you find a cheap inverter, the tubes should be reasonably interchangeable; check for sales at the local automotive dealer. (The inexpensive inverters are also somewhat insensitive to input voltage. A 12V inverter might "work" from 6 to 20V before frying anything. If you get a laptop backlight inverter, it will be more complicated, more sensitive, and more efficient.)

Thanks for the help. Is this an inverter?

CCFL 001.jpgCCFL 002.jpg

Yep. 12V (80% certainty) in on the red and black leads; positive to red, negative to black. The white wires are outputs; looks like this inverter will power two tubes. Output polarity doesn't matter. If your tubes don't have matching connectors, you probably want each connector to power one tube, with one of the wires at each end.

. What indicates that it is (probably) 12V?

Not a lot; I'm assuming that most "cased" inverters are going to be 12V. The more questionable ones are usually bare boards for maximum compactness. In this case, the case looks very "automotive" as well... (note that this doesn't hold for EL inverters for "glow wire" and simlar. They seem to regard input voltage standards with complete disdain. There are 3V inverters that have a 9V battery snap, for instance. Sigh.)

Do you have any idea how many mA/hour the tubes would draw? It might be an unanswerable question, since I'm the one with the tubes, but it's okay. Thanks again!

The small inverters I've used seem to draw a couple watts (350mA @ 5V); for two lamps and 12V input, I'd expect yours to use 500 to 1000 mA or so. (yeah, the backlight in your laptop draws a lot of power...)

Awesome, it all worked out! Thanks! The only thing left that I have to deal with is that I don't have a female connector to fit into the one with the red and black wires. I'm sure I'll figure it out though. The tubes look good. Thanks again!