Replacement bulb for microscope lamp

Olumin

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Im using a Olympus VT-II stereo microscope mainly for inspecting parts and tools and for working on watch movements. It comes with a transformer and model LSG lamp which uses a dimmable 6 - 8 volt tungsten lamp.
This is the info provided on the Olympus parts catalog:
bulb.PNG


There are a very few places that sell original replacements but they are no longer made and very very expensive for what it is.
Im guessing this bulb is using some sort of standard Bajonett and can be replaced by another standard model of bulb? Please let me know what the replacement would be. Mine is still working fine for now and has for decades but its from the 70/80s and Id like a replacement or two just in case.

Edit: ah damn this isnt even the right forum. Please move this if necessary thanks.
 
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fivemega

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It would be more helpful if you can take and post a picture of actual bulb and size (diameter) of metal base part also pins.
 

snakebite

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looks like a common 6-8v automotive bulb.
just get a lifetime supply cheap and use that glass frosting stuff.
WARNING!
the glass frosting cream contains hydroflouric acid.
handle with care.
your bulb may be near eol with the darkening i see.
 

Olumin

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looks like a common 6-8v automotive bulb.
just get a lifetime supply cheap and use that glass frosting stuff.
WARNING!
the glass frosting cream contains hydroflouric acid.
handle with care.
your bulb may be near eol with the darkening i see.
What are those called officially? Searching for 6-8v bulb does not yield any good results. Does it have to say 6-8v? Or is 8v ok? This still has to work with the transformer.

And yes its probably close to dying. But its amazing considering how long it must have lasted.
 

louie

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I don't know anything specifically about this, but a little Googling told me that:

-discontinued by Olympus in 2018
-showing as available from Hybec in Chicago (I don't know anything about the company)
-Hybec says it's an 8volt, 2A with a BA15S base and a G6 frosted globe, which looks like a 15mm diameter bayonet, like shown by Snakebite.


Your unit looks like this lamp is a separate unit on an articulated arm. Is there some lens or diffuser that goes over the housing? Your replacement may not need to be frosted, but I bet it helps. Some measurements of the dimensions fo the lamp and position of the filament might help see if the auto lamp might work. Also, how does the transformer controller work? Does it convert to DC and vary from 6-8 volts? Or is it AC? My guess is that the voltage rating is somewhat loose, and anything with a "nominal" rating of 6 volts would work.
 

Olumin

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I don't know anything specifically about this, but a little Googling told me that:

-discontinued by Olympus in 2018
-showing as available from Hybec in Chicago (I don't know anything about the company)
-Hybec says it's an 8volt, 2A with a BA15S base and a G6 frosted globe, which looks like a 15mm diameter bayonet, like shown by Snakebite.


Your unit looks like this lamp is a separate unit on an articulated arm. Is there some lens or diffuser that goes over the housing? Your replacement may not need to be frosted, but I bet it helps. Some measurements of the dimensions fo the lamp and position of the filament might help see if the auto lamp might work. Also, how does the transformer controller work? Does it convert to DC and vary from 6-8 volts? Or is it AC? My guess is that the voltage rating is somewhat loose, and anything with a "nominal" rating of 6 volts would work.
I can measure tomorrow. Transformer: http://www.alanwood.net/olympus/transformers.html
Mines the TF.

The LSG has a focusable spherical optic which screws into the housing (threads can be seen on last picture). Looks like this (not my imagine): https://thumbs.worthpoint.com/zoom/...ight_360_6f7d1eda09743db915a755246374642d.jpg
 

LEDphile

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Running an 8V lamp at 6V results in a lower output from the lamp, but a rather longer lifetime. At 6V, that lamp was likely drawing about 9W. A #81 lamp is a clear bulb and slightly lower output than stock, but is pretty close and is plenty cheap enough to try as an experiment, especially if you can find one locally - shipping will likely be several times the cost of the lamp.
 

Olumin

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Running an 8V lamp at 6V results in a lower output from the lamp, but a rather longer lifetime. At 6V, that lamp was likely drawing about 9W. A #81 lamp is a clear bulb and slightly lower output than stock, but is pretty close and is plenty cheap enough to try as an experiment, especially if you can find one locally - shipping will likely be several times the cost of the lamp.
those #81s certainly look right. Ill look into those. The ones that I can find in Germany are 6,5v. Someone suggested to frost them with etching creme, I might try that. Also looking at #81s I can see "Ba15s" and "R5W". I find a lot of results with that. 6v lamps. Also warm led ones, no idea what CRI is on those (high cri is very important for microscopes).
 
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snakebite

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looks like it.
not sure what that will cost shiped.
btw i remember several 8x series automotive 6-8v bulbs.
i would pick the highest current one and overdrive it.
none are 2a.
at $1 ea shipped for a box of 10 and a few $ for the frosting cream you are set a long time .
so what if they last 10 hours vs 100.
 

Olumin

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Just to make a quick update. The lamps that I ordered were very disappointing in terms of brightness & light quality. Even when frosted they were not suitable to be used in a microscope.

I have now ordered a Ba15s to G4 ceramic adapter (which are surprisingly common) and will use a Phillips 5761 or 7388 projection halogen lamp in it, which is specially made for such applications. The brightness is overkill but its what I have here anyway, and since I can simply underdrive them this is no problem & will prolong lamp life. This method will give me far more options.
 

electrolyte

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I've purchased a lot of aftermarket lamps for microscope illuminators, but not for many different microscopes. I've got a drawer full of 50W halogens at work right now for our Nikon inverted compound 'scopes. Fortunately, they are a common lamp used for, I believe, for some sort of theater lights. (The optics on these 80s 'scopes are superb and i got them for not much money. You'll have to pry them from my cold, dead hands.) Keep in mind that halogens were used for color temperature/photography reasons. The lamp intensity can be adjusted by voltage for observation purposes if not photographing in color. For photographs (tungston film) you had to you've got to fix the voltage in a specific range and slip some neutral density filters in the path if that is too bright.

This obviously does not apply to this stereomicroscope situation, but the illuminating light in a compound microscope must be focused on the specimen just as the image-forming light. I found out that the wrong lamp can make this difficult. I once bought a hand full of no name 50W halogens and noticed the the filament was oriented 90 degrees to what I was used to. I could not get them aligned well in my 'scope and tossed them into the trash.
 

fivemega

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Can you pot a 5761 bulb into automotive bayonet base?
I have done that and you need to be extra careful.
 

Olumin

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i noticed this bulb with vertical filament.
would it focus better in a reflector?
The lamp does not utilize a reflector. I doubt it would be possible to fit one.

I see Osram selling G4 with vertical filament. Might be interesting for flashlights. Particularly Osram 64275, 64265 & 64250. I am unsure tho, since some dealers show pictures with vertical filament, and others with horizontal. Exact same product designation, different product pictures.
 
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