CARVER TFM 15 Power Amp meter Lamps
- Thread starter AnthonyD
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Hello
Yes, but I did not see any voltage reference to the meter lamp nor amperance
It’s there in the schematic- it’s not in the block diagram. Are you able to understand schematics? I’m not trying to be a jerk. I just don’t know what your level of understanding is and I could just tell you the answer, but I think it’s better for you to find it on your own. It took me less than 30 seconds it’s not hidden just look for the meters. You’ll see the lamp you’ll see the voltage, just follow the line back to the source.
One last thing I see they are in series which means if one burns out the other one won’t work either. A ohm meter would tell you which one doesn’t work but you may want to just replace them both anyways so they’ll look the same. And again, since I don’t know your level of electronics understanding since they are in series, once you spot the voltage, divide it in half and that’s actually the voltage that you want to search for in a bulb.
PCMALO
Member
So it looks like the original TFM-15 bulbs were probably 6V. Plenty of sellers on the auction site are selling 12v bulbs for the TFM-15. So would two 12v bulbs in series be brighter or dimmer than two 6v bulbs in series? There are also some 8v bulbs available so maybe that would be a good compromise depending on whether one would like a brighter or dimmer illumination?
Hello
Thanks for your response. I called someone at the carversite, I think it was just a saleman who looked up from a schematic what the correct meter bulb voltage should be. And, he couldn't even come up with the right voltage value. I think its 8V @ 300mA? Yes, many sellers on e-bay are selling various voltages. I do lots of vintage restorations and upgrade and I really never cared for LED's since I like to keep the original design parts. So, I think its an 8V bulb. According to ohms law in a series circiut if 1 bulb burns out they all burn out except in parrallel circuits. But, I still would like to know what the actual voltage is??
Thank yo
Anthony
PCMALO
Member
Well the schematic shows a voltage to the bulbs as being 13.6v. But what I'd love to know, due to my limited electronic knowledge, is whether two 12v bulbs in series is brighter or dimmer than two 6v bulbs. I would assume the illumination level of two 8v bulbs would be somewhere in between.
audiotemp
Super Member
Voltage does not determine the brightness of a bulb. Wattage (volts x amps) does. That said, two 12v bulbs in series driven by 14v total is likely to not be very bright and two 6v bulbs in series there are likely to burn out quickly.
PCMALO
Member
Yep, the originals are indeed frosted, axial bulbs. The bulbs I'm looking at on eBay are all axial and 99% are unfrosted. They also vary between 100 and 200mA, so the 200mA versions would be the brightest, right? I don't need them to be super bright, so I'm thinking to get a couple 8v, 150mA bulbs and rough them up a bit with some sandpaper. I would just like them to illuminate the meter needles now that I've fixed them and they react normally. I don't need them to light up the room!
One of my original bulbs still works but I don't know if there is a way to determine its voltage and amperage by looking or measuring. The only measurement I get from it is about 16.5 ohms from terminal to terminal.
It sure would be nice to know the actual voltage and amperage of the original Carver TFM-15 meter bulbs ...
I don't have the answer to your question but I bought the axial leaded ones on eBay for my TFM-15, they were listed as 12v 150ma and they are a perfect brightness. Not super bright, not dim.
I also have a carver tfm-35 that's still on the original bulbs and it the tfm-15 with these new bulbs matches it.
I also have a carver tfm-35 that's still on the original bulbs and it the tfm-15 with these new bulbs matches it.
PCMALO
Member
Also mine are clear glass not frosted. I don’t recall what the originals wereExcellent info, thanks a lot!
Excellent info, thanks a lot!
Here’s a pic hard to get a good one but this one came out pretty accurate
audiotemp
Super Member
Here's a better answer about under- and over-driving bulbs.
A 12v bulb driven at 7v (~60%) will draw about 75% of its rated current, produce only about 20% of its full-voltage light output, and last up to 500 times its rated lifetime.
A 6v bulb driven at 7v (~120%) will draw about 115% of its rated current, produce about 180% of its normal light output, and last only about 10% of its rated lifetime.
A 12v bulb driven at 7v (~60%) will draw about 75% of its rated current, produce only about 20% of its full-voltage light output, and last up to 500 times its rated lifetime.
A 6v bulb driven at 7v (~120%) will draw about 115% of its rated current, produce about 180% of its normal light output, and last only about 10% of its rated lifetime.
PCMALO
Member
Well, if the original Carver bulbs were 6v, that might explain why they burn out so reliably and quickly!
audiotemp
Super Member
I guess it's possible that the 13.6v in the schematic is supposed to say 12.6v, in which case two 6.3v bulbs in series would make some sense. Then 150mA through the 10 Ohm series resistor would drop the 14v indicated before the resistor to 12.5v, and every thing would be hunky dory---except as you say the bulbs would burn out pretty regularly---which I guess they did.Well, if the original Carver bulbs were 6v, that might explain why they burn out so reliably and quickly!
Bob was genius so maybe he was sourcing magic bulbs (or whatever) that would have a decent lifetime even without under-volting them?
