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

[bob p]

I'm looking for a light bulb that has been VERY difficult to find:

Stanley 8V, 0.25A bulb. Its a "pigtail" type bulb with two wires coming out of the back.

I've also seen them rated as 8V, 0.3A or 0.35A.

This bulb was very common in Japanese built HiFi gear in the 1980s. It was often used to illuminate power meters. The bulb mounted in a blue rubber boot that was pressed into a cutout in the plastic meter assembly. The two wires came out of the back of the boot.

Does anyone know where to source a part like this? I've been looking high and low without any luck. I think that the bulb just might be unobtainable.

If all else fails, I guess I could convert the electronics over to use a different bulb, but finding the right part would be a lot simpler than modding a bunch of gear.

TIA.

[Enzo]

I have a huge bag of insulated wire lead bulbs. Most are unidentified. Whenever I need one, I get out the bag and connect them up one at a time to the voltage I need and find one that works. The wire colors do not seem to follow a pattern

Did you know that in the regular miniature bayonette base bulbs - like the #44 or #47 found in Fenders - the color of the glass bead means something? The two suport wires that stick up to hold the filament are imbedded in a small glass bead. The color of the bead indicated filament type. At least to a degree on some of them.

The 44 draws 250ma and has a blue bead. The number 47 draws 150ma and has a brown bead. There are also pink, green, white beads. I have to admit I don't know if they follow this anymore, but it was the case back in the day.

I'll see if I have any leaded bulbs bagged as 8v. I just gave a buddy some 8v bayonette bulbs for an old Pioneer reverb unit last night. 8v lamps were common in Asian stereo gear indeed.

But meanwhile, check out MCM stock numbers:
25-140
25-160
25-500

www.mcminone.com

Oooh. WHile at MCM, check out the bulb puller tool. Stock number 25-2520. It is a rubber tube that fits snug icer a bulb, so you can install a bulb in a recesssed socket. Ever have trouble getting agrip on a bulb down in a hole? I hav ebeen using one of these for 20+ years, and when you need it, it is a lifesaver.

[bob p]

I never knew that they were insulated wire bulbs. I thought that they came with short naked wires on them.

The 44 draws 250ma and has a blue bead. The number 47 draws 150ma and has a brown bead. There are also pink, green, white beads. I have to admit I don't know if they follow this anymore, but it was the case back in the day.

i didn't know that. but then there are lots of things i don't know.

is that a general truth for all of those little bulbs? for example, would a 12V bulb with a blue bead draw 250mA at 12V, an 8V bulb with a blue bead would also draw 250mA at 8V? So the blue bead means 250mA at whatever the lamps rated voltage turns out to be?


I've been looking for that Stanley 8V 1/4 mA bulb for quite some time -- its the last step that's needed to finish the repair on that Carver M-500t. Interestingly, I found the same bulb last night in an old Kenwood integrated amp that had a lazy meter in the right channel (shorted diode).

Here's a picture from the Carver. the plug sits in a blue rubber boot, and the blue boot fits into a round hole that's bored into the meter plexiglass. The light actually enters the horizontal piece of plexiglass, but illuminates the vertical segment after it bends. maybe they're doing a total internal reflection sort of thing. Here's the photo:

[bob p]

here's another photo of the bulb i need.

that's not my bulb, my photo or my smokes.

but notice the blue bead!

[bob p]

the MCM 25-500 is kinda small (micro size), but its got the right voltage and current rating.

are the full-size bulbs like the ones in the photos above really that hard to source?

[Enzo]

I didn't realize you have tha large one. Most of them are smaller.

Bulbs come both with bare leads, and with insulated wire attached, depends on what the OEM wanted.

If I recall, if you pop the bulb out of the rubber boot there, you will find bare wires with the insulated wires crimped on. It would be no problem to rewire a new bulb, but the original part likely came with the trailing wires. AH! I see the second photo shows exactly that - crimps. Solder would work as well for you.

Is that glass bulb the same size as the glass on a #44? Nothing would stop you from tack soldering wires to the brass base of a regular 8v bulb.

As to the bead thing, all the blues I could see in the chart were 250ma. The other colors were not as consistent. WHat was consistent was that a particular number bulb would always have its proper color. Exactly how the code worked is lost to history as far as I know. I found it interesting that the bead color was not simply random or decorative, it was official.

Given an 8v rail, a 6.3v bulb, and 250ma draw, a series resistor of about 6.8 ohms would make it work. At about half a watt dissipaetd, a 1 watt or larger resistor needed.

It is still possible I have one of your lamps. I'll dig through it here on a break.

[bob p]

I didn't realize you have tha large one. Most of them are smaller.

yes, the OEM lamp is kinda large, but then the Carver meters are HUGE, maybe 4x3 inches each. the amp actually uses two of those bulbs, one for each meter.

Is that glass bulb the same size as the glass on a #44? Nothing would stop you from tack soldering wires to the brass base of a regular 8v bulb.

Believe it or not, I had actually thought about soldering a wire to the base of a screw type or bayonet type bulb, but I thought that approach was too much of an amateur hack, so I didn't give it any serious thought. I kept having visions of the wire popping loose off of the bulb's tip because of the lack of a good mechancial connection. (I'm a "wrap the wire around the turret" type of guy, you know.)

I still haven't found a decent source of 8V bulbs (regardless of base type). It seems that 8V bulbs aren't very popular any more.

i dug through my box of old bulbs, and i did manage to find a GE type 44. Yep, it has the blue bead. The bulb I'm looking for is a bit larger than a #44, so it would seem that a #44 would fit in the hole. then all that I'd have to do is to modify the supply voltage. I'm still a little worried about the solder connection though -- the bulb would be too skinny to fit well into the rubber boot, which would mean it would be hanging upside-down by the wire that's tack soldered to the tip of the bulb.

I was thinking that if I had to go the route of soldering onto a bayonet or screw type base, maybe a #51 would be a pretty close match -- 7.5V, 0.220A. CEDist has those.

Taking the complete opposite approach, I had also thought about buying some 14 VAC pigtail bulbs and changing the little lamp transformer in the amp, though that would be a last resort.

By any chance would you have a spec sheet that shows the number of lumens for that OEM bulb? I've never been able to find data for it, but that's probably because all of my data sheets are new and that bulb seems to be old and out of production. optimally i'd like to find something that produces the same number of lumens. but i don't even know where to start. a vintage spec sheets might help.

[bob p]

BTW, I've found a slew of old Tung Sol T3-1/4 bulbs, and I have no idea how they're rated. They are a T3-1/4 screw type base, and some of them have the number 2.4 on them followed by a triangle. They have a white bead. I'm guessing that they're a 2.4V bulb, but I don't know the current. I was wondering if your chart might list something like this. Thx.

[Enzo]

All the references go by bulb number. Or we can select a size and shape and go down the voltages to find a bulb number that fits our application.

As to soldering to bulbs, the tip is lead anyway, so soldering to that should be reliable. I worry about the shell. I usually abrade away the finish with my fiber eraser or a file to expose the raw brass. That takes sodler well. I don't worry about it coming off any more than the other solder joints.

Amateur is when you do it instead of just getting the right part so you don't have to spend your allowance. When you do it when the options are faking it or not doing it at all, then it is "resourceful."

Lumens??? Who knows, the 8v bulbs don't seem to have an identity. But you can tell how bright a 44 is, and look up its lumens. Then compare that to the 51 or whatever bulb you consider. SOme of the 6v long life bulbs - like 10,000 hours - are much dimmer than standard use 44/47.

If you have to mount a smaller bulb in the boot, set it to where the filament lines up best for the illumination required, then smear on a dab of silicone to keep it there.

If you are going to mount a special transformer, why not stick to 6v? The really common bulbs can be used.

In my 1957 ref book, I see #41 bulbs: white bead, 2.5v 500ma, T3-1/4 mini screw. #43 same thing in a mini bayonette. My contemporary catalog (SHogyo) shows the same. I can't find my Chicago Miniature book, am trying to download a new one now.

I have a few 12v lamps similar to the one you need, no 8v. I have just a few 8v mini bayonettes, but I do seem to have a pile of 8v in a screw base. Yes T3-1/4.

[bob p]

Amateur is when you do it instead of just getting the right part so you don't have to spend your allowance. When you do it when the options are faking it or not doing it at all, then it is "resourceful."

I feel better then. I'm moving my way up the ladder.

Lumens??? Who knows, the 8v bulbs don't seem to have an identity. But you can tell how bright a 44 is, and look up its lumens. Then compare that to the 51 or whatever bulb you consider. SOme of the 6v long life bulbs - like 10,000 hours - are much dimmer than standard use 44/47.

I don't have a Chicago mini catalog, but there is a LOT of their stuff in the Allied catalog that I've been using as my Chicago mini reference. I checked with all the "usual suspect" distribitors and I've had a devil of a time finding info on some of the older bubls. It seems that 8V bulbs have gone the way of the dodo. Perhpas that's why they're not listed in the newer catalogs.

The best spec sheet I was able to find online was the Sylvania miniature & automove lamp data sheet. Its got 3 pages of bulbs listed, but some of the dodo bulbs aren't listed.

Here's the information I had found that was helpful:

Bulb #   Size      Base           Life  Lumens  Amps   Volts
41       N/A
43       N/A
44       T-3.25    Mini Bayonet   3000  11.2    0.25   6
47       T-3.25    Mini Bayonet   3000  6.32    0.15   6
51       N/A

So although I don't have data for many of the bulbs we've been discussing, I do have data for the 44 and 47, and I have both of those bulbs on-hand for experimentation. I was just hoping to find data for the 8V 0.25A bulb so I'd have a reference point.

If you have to mount a smaller bulb in the boot, set it to where the filament lines up best for the illumination required, then smear on a dab of silicone to keep it there.

does the silicon separate from the rubber boot easily when its time to change the bulb, or does the silicone get you through a one-time repair? I I have been giving thought to dispensing with the rubber boot, and adapting a bayonet socket. It might require drilling/tapping one hole into the plexiglass for mounting. I'm not too keen on that. It might crack.

If you are going to mount a special transformer, why not stick to 6v? The really common bulbs can be used.

its REALLY tight in there -- I had a lot of trouble accessing the screws to get the 8V transformer out. its practically un-doable, even with a 12-point box wrench, without removing the amp's PT and a lot of other wiring. if i'm forced to go the transformer route, i'd prefer the tiniest transformer I can find, as most of the low-voltage low-current transformers I've looked at seem to be too large to fit. perhaps something in higher voltage, like 28V would take up less space.

[bob p]

Lumens??? Who knows...

One of the things that several "resourceful" people have tried to do with the Carver meters is to replace the incadescent bulbs with LEDs. I havent' seen a good adaptation yet. All of them seem to suffer from one of two problems: suboptimal power supply adaptation, and insufficient illumination.

I saw one fellow who took a group of 3 LEDs, arranged them into a triad (held together by silicone), and stuffed the assembly into the 8V lamp's rubber boot. The resulting meter lights were pretty dim even though he was using high intensity LEDs. The high intensity LEDs trade off beam angle for intensity. Instead of having a wide angle of illumination, they have a very narrow beam focus of about 8 degrees. When mounted perpendicularly to the plexiglass, they don't provide a lot of direct illumination into the plexiglass, to do the "total internal reflection" thing. Even the bright LEDs are still pretty dim compared to an incadescent bulb. I think that more illumination is needed. But it would help to know what type of luminosity is provided by the OEM 8V bulb, just for reference. Then there's the alignment problem wit the narrow-beamed LEDs.

The other issue I've seen in the on-line LED adaptations is that nobody bothers to provide a scaled DC power supply that's spec'd for the LEDs. Most of them seem to just hook up LEDs to the AC supply, and it if works, the project is finished. I haven't seen any rectification, regulation, voltage dropping resitors, current limiting resistors, etc. They just hook up the LEDs, see that they light up, and stop there.

[Enzo]

I don't know that CMI et al ever made the 8v lamps, as far as I know, they were a Japanese phenomenon.

Oh, silicone generally peels off tings - somethings better than others maybe - but it usualy comes off easily enough.

[Steve Conner]

When the going gets tough, the tough get... Side emitting Luxeon LEDs
http://www.lumileds.com/products/line.cfm?lineId=1

The side emitting models are designed for firing into holes in light guides and plexiglass signs, and they are rated at a whopping 1 Watt

[Enzo]

Watt!!!!

[Steve Conner]

Yes, 1 watt, Bob will have to wear sunblock anywhere near his hi-fi!

I've had reasonable success in making my own edge-lit plexiglass faceplates. I use 1/8" clear plexi with the legends I want laser-engraved into the back side, and a bunch of 3mm ultrabright LEDs firing into the edge of it.

That is the problem: they have to shine into the edge, and if you just stick a bunch together like that guy Bob mentioned, the light comes out in the wrong direction and gets wasted. The side emitting Luxeon was designed to solve that problem, but I'm sure you could achieve something just as good by tinkering with regular LEDs, 2-part epoxy and a Dremel.

BTW, the blue lit bridge they show on that page is actually in my home town