JazzDad said:
The other way around would be bad: running a 12V siren on 6. It would sound like a Chevy Luv starter motor.
I've actually seen that done. Chapel of the Roses Funeral Home in Odessa many years ago had a 1955 Ford Sedan-delivery as their first-out ambulance. It had a roof-mounted Q, two red Federal FS3 single-faced lights, one on each side of the siren, and a PropelloRay light on the front center of the hood. The car was originally 6-volt, but it had an 8-volt Jeep battery. Downside was that the Q was a 12-volt siren. If they let loose on it, it would get just above 1/2 speed and then taper off.
When I worked for their competition, Rix Funeral Home, from 1963-66 that old Ford was Chapel's 3rd out ambulance. In November of '63 we were on our monthly police rotation. All three funeral ambulance services had been running crazy that day because of an explosion at a Phillips gas plant north of Odessa. Three serious burn victims had been taken to Medical Center and were undergoing surgery in preparation for flying them to the Sealy Burn Center in Galveston, which was the only major burn center in those days. So the first-out ambulances from all three funeral homes were stationed at the hospital to make the transfer from there to the airport. Just after noon my boss and I ran on an MVA in downtown Odessa right next to the Central Fire Station. When we got about a block from the scene we could see Chapel's old '55 Ford sitting in the intersection. Mr. Rix made a sour look and said, "Well hell, looks like they've beat us!" But we looked closer and it was Chapel's old Ford that had been in the accident. They were transporting from an industrial accident and had gotten hit in the intersection. The guy who hit the ambulance claimed that he neither saw or heard them. I could understand why he didn't hear the Q if it was only at half-speed; but the guy got the ticket for failure to yield to the ambulance. I used to tell my boss that we needed to trade our 6-volt 28 for the 12-volt Q on Chapel's Ford. We would've had a good 12-volt siren and Chapel would've had something that could've been heard! Never happened!