Adding volume control to electronic siren

[Henry455]

I have a Heathkit 55 watt vehicular siren I built many years ago. It has become somewhat of a collectible and I would like to add a gain control pot somewhere in the pre-amplifier section to adjust the volume for demonstration purposes.. Was wanting input on where the best place to add it would be. I have supplied a link to a pdf of the schematic. Thanks in advance for any input.

http://dl.dropbox.com/u/3598300/GD18Sch.pdf

 

[(*steve*)]

There is a gain control shown there as R27. Does yours not have this?

 

[Henry455]

Steve, that gain control is for the PA function of the siren, when you select the siren tones with the rotary switch, the tone multivibrator output signal is fed directly to the first preamp stage (Q7) bypassing that gain control.

By the way, this is the gear I am talking about: