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Carver Amplifier Lights

mingodog

mingodog

Mingo The Wonder Dog !!
Does anybody know what voltage are the meter light bulbs on the Carver TFM amps ? I need to replace them but don't want to pay the 20.00 bucks that people on ebay want for a couple of $2.00 bulbs that can be bought at a radio shack or similar store... any help is appriciated. :thmbsp:
 
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mingodog said:
Does anybody know what voltage are the meter light bulbs on the Carver TFM amps ? I need to replace them but don't want to pay the 20.00 bucks that people on ebay want for a couple of $2.00 bulbs that can be bought at a radio shack or similar store... any help is appriciated. :thmbsp:
Click to expand...

You could measure the voltage present to them and either source appropriate new bulbs or wire in LED's.
 
I'm getting a TFM-45 shipped to me next week :banana:
I'd be curious to know this too as I hear they burn out quickly.
 
Rich, I have a TFM-75 with the lights still working but from what I hear they will fail, could you post a sketch/schematic for the mod you performed to your Carver?

And yes, I can shake the whole building from the foundations with this thing... :D

Toni

pustelniakr said:
I got tired of the meter lamps burning out on my Carver, so I put in some white LEDs. Sweeet! :thmbsp:

Rich P
Click to expand...
 
kerozene said:
Rich, I have a TFM-75 with the lights still working but from what I hear they will fail, could you post a sketch/schematic for the mod you performed to your Carver?

And yes, I can shake the whole building from the foundations with this thing... :D

Toni
Click to expand...

The unit I modified was a TFM-35x. It is currently installed as the power amp for my congregation's sound system. The mod was so electrically simple, that if I did draw a schematic, it probably was on a scrap of paper, which I kept only long enough to complete the job. It is really inconvenient for me to try to open up the unit to refresh my memory.

Essentially, what you need, is a resistor in series with the LED. It is possible that the original meter lamps (2) were in series, and were supplied with a DC voltage. If I recall, the lamp board, actually had a pair of pads available to install the resistor, with a jumper installed.

The positive supply voltage goes to the top of the resistor. The bottom of the resistor is tied to the anode (+) of the LED. If the two lamps are in series, the cathode (-) of the top LED is tied to the anode (+) of the bottom LED, and the cathode (-) of the bottom LED is tied to the lamp supply return (-). If the lamps are not in series, the cathode (-) of the single LED is tied to the lamp supply return (-), and you will need a duplicate circuit for the second LED (resister and LED), tied to the lamp supply in the same way (parallel connection).

Now, if the lamp supply is A/C, you will need to put a steering diode across each LED (cathode to anode). This is so the LED is not reverse biased more than a volt or so, during the negative half-cycle (current will flow through the diode). LEDs don't like to be reverse biased. To pick the resistor value, subtact the on-state LED voltage (if in series, 2x LED voltage), at the recommended forward current (typically around 2v per LED) from the lamp supply voltage, and pick the resistor value so the the remaining voltage is dropped across it at the desired forward current: R (in ohms) = remaining voltage (in V) / forwardCurrent (in amps)

The resistor power rating should be at least twice the power dissipated by the resistor: P (in watts) = forwardCurrent * forwardCurrent * R

I'm not is a position to draw the circuit, but maybe another can do it.

You will need to orient the LEDs so that they do not shine directly into the meters, cause the illumination will not look good. Instead, aim the LEDs into white reflectors, that bounce the light into the meters. That way the light will more evenly illuminate the meters.

I hope I haven't confused you too much.

Rich P
 
I don't know if they are the same as the MXR130 receiver, a fuse style lamp with wire out of each end, but I just went down to the shop and checked the service manual. It calls for a 12V 70mA lamp.

Rob
 
Just a note on the "white" LEDs...

The light produced is actually created by passing the light from a blue LED through an amber phosphor, so the light is slightly bluish. With my Carver, which has silvered meter scales, this looks most excellent.

I just thought you should know...

Rich P
 
BroonsBane said:
Rich, you have a good pic of how she looks lit up?
Click to expand...

I have no pics of the unit, but I can "try" to remember to take a couple when I go to services tomorrow...

Rich P
 
OK. Here are a couple of pics, showing what the white LEDs look like in my Carver...

Both Meters.jpg
System.jpg

Rich P
 
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I am pushing this subject up. I am looking for source to buy the lamps from. There is a guy on Epay asking an arm and a leg for his lamps. Does anyone know where to buy the lamp for a Carver TFM 15cb?

The solution from Rich is excellent and one day I'll try it.
 
I just restored the images that somehow had gotten lost.

When ready to do the LED version. I got my white LEDs from Radio Shack. As you can see, they worked just fine.

Rich P
 
LEDs do not generally come in voltages. They come in currents.
  1. What you need to know is what current an LED is designed to operate at.
  2. Then you need to know what DC voltage is used to supply the original lamp. (Note that, if the original voltage is AC, rather than DC, you will have to modify the circuit that you come up with to drive the LED, because LEDs hate to have reversed voltage on them. You will need to add some kind of rectification.)
  3. Then, you need to know what voltage you will measure across the LED, when it is operating at the specified current. This voltage does not vary much, once the necessary minimum operating current is reached.
  4. Then, you put a resistor in series with the LED, sized so that the voltage left, after the LED takes its part, will be measured across the resistor at the operating current of the LED. The resistor must be physically sized to be able to handle the power consumed by the resistor, without damaging it (heat).
The above is complicated. Some manufacturers have come up with LED-resistor combinations for specific voltages. There may be some who make such combinations that include the ability to handle AC voltages. You will need to measure, or see in a service manual or schematic, the voltage that the lamp will need to handle. Then search for the combo you need.

The amp I discussed above was a one off, and I have not needed to go back in. I did the lamp replacement on the fly, so if there is documentation for the design, I left it taped to the inside of the amp. I do not remember the requirements or the design. I still have the amp, but it is installed in a sort of auditorium, where I speak regularly. I do not have access to take it out of the system, open it up and measure...

Sorry.
Rich P
 
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