Batboard

Not really a Motorola question, but what do you all use for testing sirens??? Have several to repair and need a quiet way to test them in the shop. I have a couple ideas, but wanted to see what other shops are doing?? Any help would be appreciated.

get youself a bank of wire-wound resistors that equal 150 watts and about 6-8 ohms. That will load it properly. You can install a small speaker with a volume pot across one of the resistors and adjust to your desired level.


Or....


just duct-tape the output tube of a speaker driver and seal it in a box packed with foam.

If you have an old speaker lying around, muffling it is the easiest way.

A standard siren speaker is 11 ohms. For a siren rated at 200 watts it uses 2 speakers in parrallel (5.5 ohms).
We use 2 x 10 ohm resistors with a switch to turn off 1 resistor (100 watt or 200 watt mode).
We have a small speaker in the test box with a volume control and a seriers resistor to knock it down to a low level to hear whats happening.
We have a meter on the box as well to display the voltage (wattage) across the sirem o/p so we can check level.

Fair Radio sells 100W 6-ohm resistors....

The large wire-wound resistor works well as a Dummy Load -
BUT be sure to mount it with the supplied stand-of brackets -
It will get VERY **HOT**!!

A good way to check what's going on during the test is to
monitor the output with a Scope connected across the load
resistor - verify the square wave outut isn't too badly distorted
to prevent early final stage failure.

jim wrote:get youself a bank of wire-wound resistors that equal 150 watts and about 6-8 ohms. That will load it properly. You can install a small speaker with a volume pot across one of the resistors and adjust to your desired level.

I bought one of the wooden wall mounted PA speakers. It has that nice "vintage" look to it. about 12" square with a slightly sloped front.

The back has a piece of perf board with a bunch of 10 watt wire wound
resistors.

The top has an L-Pad to control the speaker volume. Essentially, I wired the resistors up as a 20 dB pad. It's STILL plenty loud sitting in a shop, but the L-Pad lets you turn it down enough that the other techs don't start throwing things at you.

Jeff