Originally Posted by Kmonk
GK has a similar bulb like fuse. When I was using GK I had to replace one and was told that while they look like an automotive bulb, they actually have a different filament in them. I would email Ampeg's customer service department.
Not so. At least not for Ampeg. They are straight-up stock bulbs.
usually the number is on the base, often stamped in, but may be just stamped in ink.
The 1156 is a 12V 2 amp bulb, which I don't recall being used, although I don't recall all the cabinets and crossovers. Many cabs used a 28V 1A truck light bulb with a somewhat funnel-shaped glass bulb.
The 28V 1A bulbs were used because the 1A was near the power rating of the tweeter, and the 28V would absorb a good deal of excess voltage.
Bulbs are used to begin with because they have a low resistance when cold, so unless a lot of power is put through them, they are pretty much out of the picture. With excess input (and current flow), they heat up, their resistance goes up, which limits power flow into the tweeter.
Later cabs use several 12V tubular "dome light" bulbs in series, with the only difference being that they have an extra wire welded on each end for soldering into the PCB.