I'm messing with my gauge bulbs trying to increase the lumens. I installed a bunch of the #293 bulbs as suggested in another post and they are pretty dull. About the same as the 1895 OE bulb. So as I'm pulling the old bulbs I notice there are a couple of real bright ones in the center cluster. They are either a 755 or 55...the 7 looks more like a T but whatever. There are both 755 and 55 mini bulbs around. But, both of those bulbs are 6 volts even though they are marketed under auto indicator lamps. In fact, there is a 755 offered as an aircraft lamp bulb with a 50,000 hour expected life...for 99 cents each. I like that....OK the question, what is the deal with the voltage on these mini bulbs? I see bulbs down into the 5 volt range and up to 14.5. Would a 6 volt bulb run brighter in my 12 volt car system then intended and prematurely fail? Or is there something reducing the voltage in the system? Its a royal pain to access the tach/speedo bulbs so I want to install long life bulbs and forget about em....

Thoughts?

The OE 1895 and 293 are both 14 volts.

ALL bulbs in these cars were 12v. A 6v bulb will definitely be brighter, but prolly won't last as long...it really would depend on how much you actually drive at night, with the lights on.
One caution about using brighter lamps, tho....brighter usually means hotter...that tends to melt things.
You could do the LED upgrade, and have both brighter, and longer lasting instrument lamps with less heat, and less draw on the 'lectrical system to boot.

I've been thinking about installing 1 or 2 LED bulbs into each gauge....that way the dimmer has some effect and maybe I won't need my sunglasses to look at the gauges? I dunno....such a simple concept without a simple answer.

But how would those 6 volt bulbs be used in cars and small aircraft? There must be something that reduces the line voltage right? Otherwise premature failure seems imminent.

Running a 6 volt bulb on 12 volts will make it burn brighter and hotter and it will most likely melt your plastic.  The plastic used does not like the extra heat.  I have a section where the previous owner put in a brighter bulb and it deformed the plastic. 

Yes I understand the dangers of the heat and decreased life. I was just questioning how those 6 volt bulbs are used in what is typically a 12 volt system. And the research shows that the OE 1895 and the suggested (I tried them and they are dim too) 293 bulbs are all 14 volts. So their wattage/lumen ratings are at 14 volts, not 12 making them dimmer then expected in our 12 volt systems. A couple LED's here and there may be the best solution. Worth a test considering the price is low. 

I agree and have tried to find 12v bulbs just to get a little brighter and have never found them.  mixture of LED and standard may work let us know if you try it and can see how it works.  I think most of the guys do not use their Vettes as daily drivers which I have and will continue even when it has new paint.

I went with tb2k82ce suggestion on my 68 and got rid of the 1895 and went with the 293. I haven't finished with the complete dash harness yet, but when I made a trial check on the lighting I did notice quite a difference in the 293. I think it gave me a 16 % increase in the lumens, and it is noticeable.