Why did my sealed beam blow?

[silverdorking]

Hi, can anybody advise:-
convertible needed new sealed beam for its mot. Sent for one off eBay and connected it up. Illuminated on main beam for maybe 2-3 seconds then extinguished. Tried it on dipped and same occurrence. Do I conclude that I've 'blown' the unit? If so why/ how? Can't see anything obviously wrong with wiring, any ideas?

[oliver90owner]

It likely has a leak somewhere, allowing the inert gas out and air in. Air plus white hot filament is not a good combination - and they did! May not have been degassed properly at manufacture. Nothing to do with your car being a convertible!

Could also be a 6 volt unit on 12 volts? Never seen a 6 volt sealed beam unit, mind.

[silverdorking]

Thanks for this, definitely not a 6v. Thanks for eliminating convertible issue! No sign of seal failure, I'd no obvious cracks etc!

[ManyMinors]

Secondhand sealed beam units, unused for a long time, often seem to have very short lives. They are usually very reliable but last time I had to replace one, I found 2 or 3 working spares in my garage. Once fitted though none of them lasted long
They don't seem to like sitting on a shelf for years on end.......

[biomed32uk]

For the work and effort involved do the halogen conversion, they work just fine and all you have to do is change an H4 bulb then.

I don't drive her at night much but on the occasions I have the lights are pretty good, and more than enough for what the car is.

[bmcecosse]

Old sealed beams often blow - the air leaks in over time, especially when not 'used' when tiny amounts of air would be burned up by the filament as it goes along. Generally a waste of money buying old sealed beams - I dumped at least 6 old ones without even bothering to test them, which I had 'saved over the years ' a couple of weeks ago.

[silverdorking]

Thanks all! Quite a consensus regarding the sense in fitting second hand sealed beams! Halogen replacements now on order!
Thanks again for your collective expertise!