Looking for an Odd Light Bulb: 8V .25A "Pigtail" for Meters

[Enzo]

If I had a relay with a 100ma coil current, I'd want to use at least a 200ma transistor to switch it, and preferable more like 500ma. If I look around the shop and find I have no 500ma xstrs. I surely would not pass up a 3 amp xstr in stock for the opportunity to order the smaller one. For that matter, I am sure I have soldered 1000v ceramic caps across volume controls for brightness. I doubt there will be 1000v across that pot any time soon.

The data sheet tells what currents the part can handle, and it is up to you to design in a comfortable margin for safety. Don't think there will be a lot of surge current. Beyond that, don't try to out think yourself.

[bob p]

oops. i deleted my last post when i was trying to edit it. sorry about that Enzo -- i didn't mean to make it look like you're talking to yourself.

on a related note, how much wattage rating is going to be needed in the series resistor? i don't think there will be a lot of voltage drop, and the current is going to be 350mA or less, so I'm thinking that those great big 5W resistors used in the previous example won't really be necessary.

[Enzo]

The whole point of the resistor is to limit current. Look up the natural drop across the LED, and the resistor soaks up the rest of the voltage from the rail, whatever that might be for you.

In the case where you already know the current, then I^2 R = P. Then add your safety margin - like double or triple the necessary wattage. SHouldn't be a lot.

[dd123]

Hey, did you ever find the 8V 0.25A lamp for your Carver? I need an 8V 0.3A for a Kenwood KR-6600 and I haven't had any luck finding one either.

[billybillybilly]

in regards to the odd 8v bulb ...

Hey, did you ever find the 8V 0.25A lamp for your Carver? I need an 8V 0.3A for a Kenwood KR-6600 and I haven't had any luck finding one either.

hey dd123,

some years back , i found a Kenwood KA-6150 in the trash . brought it home and figured out that it still worked , but the channel selector switch was bad (and the 8v bulb). i removed the preamp section and ran some pedals straight into the poweramp . sounded decent enough .
anyway , as far as the odd 8v bulb in it , i replaced it with (if i remember correctly) a 12v bulb of the same physical size (not to sure of the ma rating) . it was something they had in the parts bins at radio shack so i know its not a hard to source part . it worked just fine as far as a replacement bulb goes ... light up the VU meters as intended . i ran the amp hard for 1-2+hrs many times and didnt melt the boot .

[dd123]

That's great info, thanks. I'm on it! Maybe I can find a big Radio Shack that still has lots of small parts.

[jrfrond]

I have a TON of that style 8V lamp in stock, but they are bare leads and clear bulb, not blue. You can tint them with Sharpies. Let me know if you need any.

Now, if ANYONE can help me with 3V Axial lamps for an old Altec 1220 mixer, I'd be much obliged.

[dd123]

John, here's a pic of the lamp I'm looking for (the top one) and another lamp I might need (the lower one). The 8V 300mA lamp sits in a rubber boot with the leads coming out the bottom. The base of the lamp is about 1 3/16 inches in circumference. Is that what you have, either with or without the boot?

Do you have the other lamp, too? I believe it's 50mA. It has long leads -- 1 1/8 inch.

[jrfrond]

The bottom one is easy. I have those. The top one, not sure. Have a number off the side?

[Enzo]

Oh geez, I thought we were chasing these things:



Hmm, what is that little based lamp? There is no flange or bayo pins. I have lots of 8V bayo based lamps

[jrfrond]

Oh geez, I thought we were chasing these things:



Hmm, what is that little based lamp? There is no flange or bayo pins. I have lots of 8V bayo based lamps

Actually, that's what I am looking for! The lowest wattage I have is 6V. I need 3V. Practically extinct. I might have to go with LED's.

[Enzo]

MCM sells them in 6. 8. 12v. DOn;t know where to find 3v ones.

What runs on 3v? is it worth modifying the gear to provide 6v to the lamp?

[jrfrond]

The piece is an Altec 1220 mixer. The meter lamps are a series string of ten lamps fed by an unregulated 30VDC supply, which is on a separate transformer winding, so there is no more voltage available. I have those same lamps from MCM in stock, and they won't do the trick. Like I said, I will probably go with high-brightness LED's, but the issue with those is that the lighting angle is narrow as compared to a lamp, and the white is almost blue-white, i.e. very cold. I've been searching for different color temps.

[Enzo]

DOn't white LEDs have about a 3v drop? There are ways to diffuse pointy light sources, but I don;t know if you want to go that far.

And ten 3v lamps in series is abuot the same as two strings of five 6v in parallel. ANy chance there? Break the string between 5 and 6, and run wires to the respective ends to parallel them.

[jrfrond]

The series-parallel option was one that I was tossing around, but this mixer doesn't readily lend itself to modification. However, with a little "reptile dentistry".....