I recently acquired a set of the above in a swap. Inside is a light bulb with a Ba15d double bayonet base, and a shape that appears to be S8. "94 W" is stamped on the base.

Any idea where to get a replacement?

As they say, a picture is sometimes worth a thousand words. I'd have to dig mine out to see what was in them, but I'd bet its basically a standard locomotive bulb -- usually there are two variations 15 watt and 30 watt (15s11 and 30s11, I think?).

The product I'm thinking about is near the bottom of the page in this link:

http://www.epowerrail.com/pdf%20PRD%20f ... %20121.pdf

Power rail is a good source if you know what you need. Specialty Bulb in New York is a good source if you need some tech support.

Hope this helps.

ETA

Yeah, this is going to be interesting.

The B15d base is common to automotive bulbs. You can look at S8 size bulbs in lots of places on the Internet to see their sizes and equivalents. I believe this is essentially the same thing as a single-contact turn signal bulb, like an 1156. The 'catch' is that, in order to see the appropriate current to make the light on 72V instead of automotive 12V or military 24V, the bulb is rated at 94 watts.

There are a couple of approaches you could use. If the marker is to be used only for display, you could just hook it up to a 12V power source or transformer and put in the appropriate bulb (AutoZone et al. have the standards, places like Grainger have specialty bulbs like xenon or LED)

If you need the thing to work on 72/74V, a logical (to me) approach may be to use a dropping resistor arrangement of some type, as on streetcar lighting, to get the effective voltage down to where a commercially-available bulb would fit.

A more sensible approach would be to use LEDs of comparable illumination power, and put in an appropriate dropping resistor, heat-sinking arrangement, etc. Then connect this to the shell and terminal of a B15d base, and if you need to, attach a cut-off envelope over the base (be SURE your heat-sinking arrangements are good!) v There are some good online LED calculators that should make choosing the right resistor easy.

Thanks for the replies.

My intentions (if possible) was find 12V, 72/4/5 and 110 to be able to use them on what's available.

LEDS of the appropriate brightness would be great, especially for 12V

Home Depot was able to identify the wire as 14 guage, and has stock wire that's rated for 600V and has oil resistant insulation.

It's more likely I'll be using 12V.

So 94W =94 watts? Man that seems like a lot power for such a small bulb.

Anybody tell the EPA?

You have to remember that 'watts' here has a different purpose; it's to control the current given a particular voltage.

Current is what produces the level of brightness. So depending on the voltage, you want to adjust the 'resistance' of the bulb to where you get the right current.

The 12V and "94W" bulbs will produce the same general amount of light when driven from their 'proper' voltage sources. Remember E = IR and P =EI (or I^2R)?

Your "94W" bulb would nominally draw 1.31A at 72V and 1.27A at 74V. We don't care what "R" actually is because we don't really need to find it; what we care about is the 'wattage' that produces a target current at rated voltage.

The 12V wattage equivalents are (rounding) 16W and 15W respectively. That's the general range of wattage to look for at Auto Zone or wherever if you want equivalent brightness. I doubt that a fixed focus inside the bulb is really necessary for one of these, but short of seeing a picture of the filament in your 94W, I can't tell for sure (and am unfamiliar enough with the internal details of markers that I have to say so).

"Remember E = IR and P =EI (or I^2R)?"

No, my knowledge of electrical formulas drops off considerably after Ohm's law. I MIGHT be able to prove RMS voltage given the integral for Sin(x), but that's about it.

I've been informed that the "94" doesn't stand for the wattage, that"94" is a a type of bulb. Looking it up, I see that No. 94 miniature bulbs are designed for 12.8V and produce 15 mean spherical candlepower or about 188 lumens, and have the S8 globe and BA15d base.

I think, in the interest of not changing bulbs, I'm going to look for a LEDs that produce equivalent light, not terribly historical, but perhaps more practical.

Here is one page showing the size 94 bulb

And here is a link that shows the 28V version of milspec MS15584-2

I note that they say 'railroad' as an application, but that bulb would likely make like a flashbulb if you plugged it into 72V ... a 72V version of this bulb would have a VERY small rated amp draw.

My guess, given this, might be that the "W" means 'white' instead of a color like red or amber. I am looking to find a more appropriate reference for a "W" but it is not in the ANSI numerical code reference.

Perhaps they are not the original bulbs to begin with?
Mike Tillger

From what I hear, I suspect that you are exactly right.

"Perhaps they are not the original bulbs to begin with?"

So.. how do I find out what the originals were?

Easiest way would be to examine what is in an existing marker running on either 32V or 72/74V. There ought to be all manner of folk on this list who know intimately what style of socket, bulb, and wire is found in contemporary lighting.

If you know what the light came off, you could consult a supply firm that sells railroad equipment, and see what configurations of marker lamp they sell for diesel applications.

I have no idea whether some steam applications used less than 32V on lighting dynamos -- but you are in a community of experts. What you have now is explicitly running on a 12V system. The only other '94' code bulbs I have found are 28V, which is close enough to 32V that I think it might be workable ... but before putting money into something that makes the marker less convenient, I'd try the above.

Different railroads used different bulbs in their locomotives auxiliaries, even headlights. I doubt you can determine the original bulb with out knowing who the marker lights were manufactured for. Our GP9 locomotive uses 64 volt bulbs in the marker lights, 110 volt bulbs in some warning devices, 6 volt bulbs in the speedometer, 30 volt headlight bulbs, 74 volt ditchlight bulbs, 74 volt 15 & 30 watt bulbs that would fit your markers are used in the gauge lights and cab lights. Most steam locomotive marker lights used a 15 watt 34 volt medium base screw in bulb, which was also used in the gauge lights. Remember watts is an expression of power not brightness, even though that has been the term used to define household bulb brightness by most manufacturers. Markers did not need to be very bright as during daylight hours, many railroads used flags to convey the same meaning as the locomotive markers.

I went and dug out a pair of MLM markers that I purchased on eBay some 10 years ago. The bulbs were still in the markers which showed no evidence of having been 're-wired' for alternative use...electrical supply lines appearing to be snipped from their source (but again, with eBay you can't be sure). The bulb bases were marked W 1142 which on one website describes their C 1142 bulb as being "18.4 Watt, 12.8 Volt, 1.44 Amp Miniature S-8 Bulb having a Double Contact Bayonet (BA15d) base, 2 inches long, 1 inch in diameter, 21 candle power, clear, incandescent, with an average life of 1000 hours, and being equivalent to the GE 1142 and Osram/Sylvania 1142...which leads me to believe that the "W" in W 1142 stands for Westinghouse (and the "C" on the website's bulb for their manufacturer, CEC). This also makes me think that the "W" on your bulb actually specifies the manufacturer of the #94 bulb that has already been mentioned in this thread (a cursory search shows that Westinghouse no longer makes these two bulbs).



Another interesting thing I noted when 'Binging' images of 1142 bulbs was that more than 95% of the images were of LED versions of the bulb...better get those incandescents before they're completely gone (see your reference to EPA in above posting).

Hope this has been of assistance in your quest.

sc 'doc' lewis


EDIT POST-SCRIPT: When you think about it, the described markers were primarily caboose markers and in the post-kerosene steam era it would require an awful long run of your Home Depot 14 gauge, 600V wire with the oil resistant insulation to get to the power source up at the engine...let alone the logistics of the thing. Sources indicate that cabooses were set-up with generators that were belt-driven off of the turning axles, with the generated electricity being stored in batteries (hence the term "battery box"). It would seem most reasonable that these generating/battery systems would be the very common 12V system...pardon the pun, "but why re-invent the wheel?". So, IMHO, little need to wonder about Ohm's Law, 94 watts, 72 Volts, etc. It would appear that either the #94 or #1142 bulb will work for your application, be it incandescent or LED.

"very common 12V system...pardon the pun, "but why re-invent the wheel?". So, IMHO, little need to wonder about Ohm's Law, 94 watts, 72 Volts, etc. It would appear that either the #94 or #1142 bulb will work for your application, be it incandescent or LED."

Agreed. While I am curious as to the original equipment, it is very unlikely that where I plan to use it, It will be powered by anything but portable 12v power source or maybe Household 110AC.

I doubt that it's interpretive value will be affected by the guts. I just want to more or less duplicate the amount of light that would have been seen when these things were in service. All I want is to avoid some 85 year old guy saying, "hey dummy, it's way to bright (dim)".

If an LED works without looking like a midget star,cool. They last forever and draw less power.

In any case, thanks to all.