Anyone here know everything there is to know about obsolete miniature incandescent lamp bulbs?

62vauxhall

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#1
In particular, a replacement for the pilot lamp in a Realistic QA-680 four channel integrated. It's fed from the rail voltage which I measured at ~42 volts.

It's not my amp, I just offered to check it out for someone and fix if possible. None of the parts vendors I've checked so far has anything of similar physical size that uses 40 volts.

IMG_4961.JPG
 

MarkWComer

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#2
Too big to be a “grain of wheat” bulb.
Looks similar to the ones used in old Califone tonearms.
 

62vauxhall

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#9
Pilot as in 'i am on' light?

Neon??
Yeah, the "on" light. They were called pilot lights at one time and I never got past that.

No electrodes to be seen inside so I guess that's a no to it being neon. There does look to be supports inside for an extra long filament though.

Is there any easy way to adapt an LED to operate with ~40 volts DC?
 

J!m

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#12
I had something similar looking in (one of my) Kenwood pieces. The metal sleeve slides down to get to the juicy bits. I had the repair manual so I knew the voltage of the bulb in my case…

it might be a 100vac bulb that would burn dim at 40-odd volts. There are other voltage bulbs of course but they are not common.

The switches on the plasma consoles have pilot lights. They push in (120vac) and are “telephone switch lights” or something like that. A black plastic tip with to leaves on either side. Bulb has a flat top (not suggesting it’s what you need). Point is, they are available but you have to “focus powa” on your google-fu glasshoppah.
 

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#13
Yeah, the "on" light. They were called pilot lights at one time and I never got past that.

No electrodes to be seen inside so I guess that's a no to it being neon. There does look to be supports inside for an extra long filament though.

Is there any easy way to adapt an LED to operate with ~40 volts DC?
Absolutely, just a matter of the having the right resistor in series. A 1W 2.7K resistor in series will do the trick.
 

62vauxhall

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Absolutely, just a matter of the having the right resistor in series. A 1W 2.7K resistor in series will do the trick.
Well darn, I just checked what resistors I have and nothing close. But I did find a couple, or at least one, 12 volt 5mm green LED. I labled it "soft green" and it was in a bag with another 5mm LED but it is unlabled. Probably another of same.

I also have the smaller 12 volt blue LED's that came from one of your light boards. The board was for a 400 with very dark meter lenses. I had to swap blue for bright white so as to see the meter scale and needle.

I'd like to use what I have on hand if possible and I do not care if the light colour is blue or green. There are no other competing lamps present on this amplifier.

Will a 1W 2.7K resistor work with any colour LED? My understanding is that LED colour dictates resistance. Whatever the case, I need to get one or some of the appropriate resistor.

Instead of having to pay shipping costs for a few fiddly small pieces like I do now, it sure was convenient having a local parts shop somewhat nearby.
IMG_4962.JPG
 

Gepetto

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#16
Well darn, I just checked what resistors I have and nothing close. But I did find a couple, or at least one, 12 volt 5mm green LED. I labled it "soft green" and it was in a bag with another 5mm LED but it is unlabled. Probably another of same.

I also have the smaller 12 volt blue LED's that came from one of your light boards. The board was for a 400 with very dark meter lenses. I had to swap blue for bright white so as to see the meter scale and needle.

I'd like to use what I have on hand if possible and I do not care if the light colour is blue or green. There are no other competing lamps present on this amplifier.

Will a 1W 2.7K resistor work with any colour LED? My understanding is that LED colour dictates resistance. Whatever the case, I need to get one or some of the appropriate resistor.

Instead of having to pay shipping costs for a few fiddly small pieces like I do now, it sure was convenient having a local parts shop somewhat nearby.
View attachment 57324
When you are dropping 37V across the ballast resistor to power a 2-3V LED, it does not matter what color it is. The forward voltage drop only matters if your voltage source is like 5V where a small change in the voltage across the ballast resistor will make a sizable forward current difference. You can use any value resistor between 2.7K and 4.7K to do the trick. That gives you a wide range to choose from.
 

nakdoc

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#17
The original lamp is probably 12 volt. The circuit uses a series dropping resistor, something like 330 ohm 2W in series with the lamp. The voltage you measured is open circuit voltage. Once a good lamp is installed, the voltage drops to 12v. A LED conversion with resistor will work fine if you get the polarity correct
 

62vauxhall

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#18
So I have discovered. There is a 1 watt 470 ohm resistor on the power supply board in series with the pilot light bulb.

Not sure what the proper bulb voltage is exactly. I tried a couple of 12 volt miniature incandescents and obtained different voltages with different bulbs. Even though they were 12 volts, milliamperages were different.

But be that as it may, after hooking it up, it looks like one of my green 5mm LEDs with a 4.7K ohm resistor will do the trick. Not terribly bright but adequately bright.

And thanks for the responses.
 
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