I saw a flash of light coming from inside my cabinet and now it sounds different. What happened?

The protection circuit for the horn found in older SWR models such as the Goliath™ (I & II), Triad™, and Goliath Junior™ (I & II)™ enclosures actually includes a light bulb wired in series with the horn. Under normal conditions, the bulb is cool. As you begin to overload or put more power into the horn, the bulb begins to light and increase in resistance, limiting the voltage going to the horn. At high power levels, you may notice intermittent light coming from behind one of your speakers. This means that the protection circuit is doing its job and that you should probably turn down the attenuator knob. A sudden burst of feedback or a heavily clipped waveform can cause the bulb to open just like a fuse. Replacement bulbs are available and nearly all auto parts stores and gas stations (usually sold as auto "dome" lights; replacement bulb No. 211-2 is manufactured by companies including Sylvania, Phillips and Wagner).