Packard Forum Index » Pre-War (1899-1942)

While not a Packard-specific query, I was wondering why #51 and #55 bulbs (correct bulb #'s for my '39 Six dashlights) are listed as 7.5 and 7 volts, respectively?? Other bulbs I have purchased (larger ones) are listed as '6 volt'. My thought is these will work fine, just curious as to why the varying voltage designation? Chris

6v is a nominal value for convenience sake and most but not all 6v bulbs will safely work from 6-8v and some are even spec'd that way. It might be the mfg printing the 7 or 7.5v rating has some govt regulation to contend with or is just being a bit more truthful to fend off lawyers who seem to file class action suits against any mfg advertising a spec the least bit out of order.

A lead acid battery cell puts out 2.1v when charged so with 3 cells in series the 6v battery standing voltage is 6.3v. That number is immediately over the nominal 6v advertised value. For the battery to have a proper recharge from the generator the regulated generator output voltage needs to be on average 1 volt higher than the standing voltage so most 6v generators are regulated to about 7.4v. Any automotive 6v bulb will need to be able to handle that much and that is assuming the regulator is adjusted properly.

Thanks Howard - good answer. I was curious, as the #55's were in modern 'cards' of 2 bulbs, hanging with a million other bulbs on the rack, and they listed at 7 volts. The #51's however weren't there and I had to order them in a box of 10. The box looked like it came out of some NOS inventory and looked very old. These listed at 7.5 volts, thus the question. Appreciate your time. Chris.

I believe the 55 bulb has a higher output than the 51s

Hi JT120, thanks - yes it does; the 55 is a slightly bigger globe, uses nearly twice the power and IS significantly brighter. The 51's go in the gauge clusters while the 55's are for the speedo and clock backlighting. (and the map lights) I bought a box of each and think I will try putting it all back together with the correct bulbs and if I am still unhappy with the lighting in the oil/water and gas/ammeter gauge clusters, I can try a 55 in those too. As things stand, I believe I have gotten the dimmer switch to work properly and it SEEMS to take the lights up to quite a nice, bright intensity. I'll report back my findings once I have it all hooked up and working again. Thanks for weighing in. Happy New Year to you! Chris.