This circuit was found in a Philips documentation from 19678. The transistors are from the period with emphasis on the married pair. Modern equivalents can be used.
This circuit was obtained from an old American documentation, and practically any general-purpose transistor...
This circuit is intended for monitoring an environment. It fires a relay with a sound, but only if...
This circuit is from an old documentation, but perfectly current. In place of the battery, 2 or 4...