Any electronics dudes out there? Please help.

[rplace]

I have 4 carver TFM-25 amps. They are prone to burned out bulbs for the meters. A guy on ebay sells replacements in the form of LEDs rather then bulbs. He has them in both blue and original white. I would like to get some form my amps, but 20 bucks for 2 LEDs seems high to me. I would need 4 pair so it would cost 80 bucks, ouch.

I know very little about electronics, but figure if somebody pointed me in the right direction I could probably get the right parts. What do I need to know? Any sort of restriction on size, load, and wattage if there is any on LEDs. Is there anything I can look up about the amp that would help you help me?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5793007654

[Frzninvt]

Look at it this way, you buy these once and that is the last bulb you'll buy for them. Or you can get the standard bulbs in bulk and just keep changing them every time they burn out.

My DBX BX-3MkII amplifiers were the same way I had to keep a stock of replacement bulbs around and move the unit out of the rack, remove the top cover and remove a few pieces to swap out the burnt bulb. It was a pain in the butt, I would buy the LED's just so I sould not have to mess with them again.

I am pretty sure you can source them elsewhere but like to said you need the right voltage, brightness, etc.

[Hardhead]

You're really paying for the installation instructions, not the LED's. You can buy one set of LED's from the the eBay guy to get the instructions and find out which bulbs to use, and then buy the rest of the bulbs at an electronics place like Mouser, etc. for a couple of dollars each.

[rplace]

Thanks to both of you for the quick response. Instructions are not the issue. That is covered in the manual. All I really need is the correct type of LED...assuming there are different types of LEDs. I guess that is my real question. Not know much about electrical stuff I don't know if one LED is the same as the next or not. If they are different how does one go about finding the correct LED to replace a standard filament bulb. I have opened my amp up and can see that is a standard filament bulb.

[dragonfyr]

I have sent a few mails around to see if anyone knows the proper specs for the LEDS. But simply knowing the specs for the current bulbs would help alot, as then it is rather easy to determine what changes must be employed to substitue LEDS.

This is not rocket science...which is indeed fortunate as the NASA folks are a bit busy right now trying to discover the characteristics of foam!

But Digi-key is a great place to source them once we can figure out the proper values and the mod necessary.

[johnyholiday]

contact the feedbackers, an pick their brains,20 bones, skidaddy!

[dragonfyr]

Here is the preliminary reply, but I have requested the assembly specifications.

I will be happy to provide specifications on the lamp assemblies themselves. However, because these are covered only by a provisional patent at this time, I won't release any specs on the components that make up the lamp assemblies. As soon as the full patent is granted, I will be happy to provide data sheets/schematics on the internal components. In fact, I spent quite a bit of money on the plastics that are used to make these lamps. It is special tamper-proof plastic that will outsurvive the components should heat or chemicals be used.

Will post the results...

[Mark Hardy]

The whole trick, but also the only trick, with LED's is that the forward resistance is very, very low. Any given LED is rated for a specific voltage drop, and thus there is a "correct" current through it. You will almost certainly need to add a resistor in series with the supply for theoriginal (incandescant) pilot lamps to put in an LED. This is well-understood in the trade, but I learned it by testing an LED with a 9-V battery. The LED literally POPPED (exploded) from the current that tried to pass through it!

Ohm's Law is your friend!

EDIT:

Here's an LED series resistance calculator page (offered "as is"):

http://linear1.org/ckts/led.php

Another LED how to:

http://www.kpsec.freeuk.com/components/led.htm

In theory you can use an LED with an AC supply, since it IS a diode... I am guessing that you need to think about the peak voltage, rather than the RMS voltage, of an AC supply (which is probably what your existing pilot lamps use), but I am not so sure on that point.

[dragonfyr]

I will post the instructions and picture of the LEDs sent to me that are being sold on EBay.

But I wonder if you might be better off exploring the direct replacement of the incandescent bulbs with LEDs by companies such as :

http://www.theledlight.com/ledbulbs.html

This would be much easier as it would be a direct replacement.

OR:

Otherwise, I would simply look at sourcing an LED directly from electronic component suppliers and having it modded yourself. I am simply having some difficulty getting the data as I don't know what you are looking for and what 'it' is (the values specifically) that you are replacing!! (but this should be a simple matter of requesting the data sheet for the LED you like and looking up the specs on the existing bulb!!). Once you know what you have and what you desire, the mod to change the voltage and current supplied to that which is requires should be relatively simple!

[dragonfyr]

Here are the installation instructions. The basic component values are present at the end.

[rplace]

I got the install instructions too at the end it says:

Never mix incandescent and LED lamps in a series circuit.

Electrical Specifications:

8VDC

20mA

Does the 8VDC and 20mA help in determining the values I would need for the LEDs.

Perhaps, this is not as simple as I envisioned. I thought I was just soldering an LED in place of an incandescent lamp and all I needed to know was what LED to use. If this guy has actually bundled together "some components" to replace the lights and not simply bought LEDs for pennies and sold them for 10s of dollars then I would gladly buy from him.

Like I originally said I don't know much about electronics. I can hook up a surround system with the best of them. I even wired my entire basement from the breaker box to the outlets. I own and maintain two electro-mechanical (old style) pinball machines. However, when it comes to volts, amps, resistors, capacitors, transistors and the like I am in the dark.

Do you more savvy electro-nerds think this is a simple replace a light bulb with an LED or is it more elaborate and I should cough up the 80 bucks? I surely dont want to mess up the power in my amps by being a tightwad over a few dollars. On the other hand if I am going to tear it open and solder in new lamps from Carver that will burn out again why not go the LED route.

[Malcolm]

Ignoring mechanical and luminance issues, replacing an incandescent lamp with a LED is really easy. Once you have selected a LED, you just need to determine the supply voltage, the voltage drop through the LED (forward voltage) and the maximum current you can pass through the LED without destroying it. Besides the LED, you need a resistor to drop the voltage and limit the current. Assume a 12V supply, 5V forward voltage and 10 mA current. For purposes of these calculations, treat the LED like it is a 500 ohm resistor (5V/.010A) in the circuit. Once we have done this, we can just treat the LED and resistor as a voltage divider. We have to drop at least 7V across the resistor or we will destroy the LED. So, the resistor needs to be 7/5 of the that for 700 ohms (7V across resistor + 5V across LED = 12V supply). I don't think this is a standard size, so you can go up to the next standard size which I think is 750 in a 5% tolerance. It can be a 1/4 watt resistor because it only has to dissipate .07W (7V x .010A).

FWIW a blue LED, a resistor and a bit of heat shrink tubing can be had for a few bucks. I think what you are paying for with this guy is knowledge. Kind of like paying an electrician $95 to replace a blown fuse: $5 for the fuse and $90 for knowing what to do.

If you want to replace bulbs that are socketed (bayonet, screw, etc.), there are direct LED replacements made for many popular incandescent bulbs. They generally cost in the range of $5 to $20 in unit quantities. Anyone interested can find them at Digikey.