With this circuit you can produce the sound effect passing from one channel to another. The circuit is from Mullard documentation from the 1960s. The transistors may be the BC548.
This protector was found in an Electronics Now from the 90s. The 250 V transient suppressors are common...
A modulated (intermittent) siren, using the four gates of integrated circuit 4001 is shown in...
This interesting circuit appeared in the April 1952 Radio Electronics magazine. The circuit is...