Magneto bulbs and close enough

[Steve Jelf]

When I saw these pointy globes at Hershey I figured they were probably mag bulbs, so I bought some. They have the correct double contacts and even pins, but that doesn't tell the voltage, so I wasn't sure. Today I was cleaning some of them and found the markings which confirm that I figured right. The 9V is clear, but I'm not sure if the CP is 21 or 24. It looks like 21 to me.

These bulbs of a later vintage have the double contacts and even pins, but they are marked 6-8V. They're quite common. But are they any good for magneto lights? Yes, I've found that they are. When I read about mag bulbs burning out I imagined it being a frequent problem, so I was glad to find that both these types of bulbs last quite a while before they go. But I will be keeping a box of spares in the car. The problem I've found with these old bulbs is that sometimes after a hundred years or so the old glue has failed, so when you try to turn the bulb in the socket the glass twists in the base and the bulb is wrecked. If you look closely you can see that I've smeared a bead of glue around the seam hoping that will hold the glass and the base together well enough to survive installation. The glue I used was E6000 thinned with gasoline. I'll also carry a can of silicone lubricant and squirt the socket when I have to change bulbs.

[MKossor]

Steve, Are you running a "Dimmer Coil" in series with the magneto head lights? I would expect a short magneto bulb life and significant safety concern being wired in series if not using a dimmer coil considering the magneto output voltage with engine RPM can reach values in excess of 40V depending upon the magneto parameters (magnet charge and spacing WRT the coils).

Not sure if vintage dimmer coils are readily available. Here is a modern version that may work but a bit pricy to be experimenting with.
https://www.digikey.com/en/products/det ... -4/1984839

[Steve Jelf]

No, Mike, my lights are stock 1915. Ford didn't add the dimmer until late 1917. I've had bulbs fail, but it wasn't a safety issue because I don't drive where and when it would be. I avoid driving on really dark unfamiliar roads even when the lights are working, as that's too scary and dangerous. If you drive fast enough to make the lights adequately bright, that's fast enough to outrun them. My night driving is in town where there are lots of street lights, and on familiar straight roads coming home.

[Novice]

I use this plastic bonding compound to run a bead around My old NOS bulbs and prevent them from turning in the base and destroying the bulb. just run a bead around the base of the bulb and the metal socket then use the UV light on the end of the compound dispenser to harden the plastic. same stuff the Dentist uses to hold Your teeth together. works great and You can build up surfaces with multiple layers. I have one in all My tool boxes. Black end has a cap with a fine needle point under it. for applying the compound. and the other end has the UV light source used to cure the plastic takes a few seconds. hard as nails.

[RichJ]

Jim ,where can Bondic br sourced, Thanks Rich J

[jab35]

Rich: Pretty much everywhere, I see adverts for Ace, Wal-Mart, and of course Amazon. https://www.amazon.com/Bondic-Activated ... 2821&psc=1 I have no association with any seller or the product, but the stuff seems ideal for this application

[Greg Griffin]

I'm not accusing anyone of anything, but just want to mention that heat will pop the glue loose in those bulb sockets real quick; so if you're cleaning the base with a wire-wheel, take it real easy.....

[Susanne]

I'm not sure I'd use a wire brush - steel wool would probably be a lot safer... What I'd worry about (having done it) is trying to melt on new solder contacts to the base and losing the glue that way...