How
do I know which QH bulb for my old bike?
How
do I know which QH bulb for my old bike?
British
bikes used BA15d (dual filament dipping) bayonet cap bulbs from the 1920s
until early post war. Some marques, inc. Velocette & Vincent carried
on until the mid 1950s. Diag. 10  |
 |
|
These were then replaced
by the British Pre-Focus bulb Diag. 4 |
|
| 6V Dynamo systems | On pre-War bikes it's usually best to stick with 25/25W | |
| Most post war bikes fitted with the Lucas or Miller dynamos can cope with the 35/35W headlamp. There are some lower output dynamos fitted so check the output first. | ||
| If your bike was fitted originally with a 30/24W headlamp it's safe to fit a 35/35W. A safety margin was built in and also provision for sidecar lamps. | ||
| 6V dynamo systems converted to 12V | If you've got the shorter Lucas E3H or Miller dynamos 12V 35/35W is the safe maximum. | |
| If the later Lucas E3L as fitted to most twins then the 45/40W can be fitted. With LED stop/tail bulbs then the 60/55W will be OK, but note that you will be running the dynamo more or less at full output all the time. | ||
| If you're using coil ign. you're limited to 35/35W | ||
| 6V Alternator systems | All 6V alternator systems can cope with a 35/35W headlamp bulb. | |
| 6V Alternator systems converted to 12V | With points ignition 60/55W but with electronic ignition 45/45W or even 35/35W depending on the effeciency & type of the alternator, it's usually best fitting a modern one. | |
| 12V alternator systems T120, A65 etc.. | 60/55W but if electronic ignition is fitted then 45/40W. High output or 3 phase systems may cope with 100W or even 130W. 60/55W is the legal maximum and 60% & even 80% brighter Xenon bulbs are available to fit the modern H4 type headlamp so there's no reason to exceed this. |
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