This amplifier was found in a 1970s documentation. Darlington transistors can be replaced for modern equivalents of at least 80 V x 2 A, equipped with good heat sinks.
This sound relay or Vox was found in 70s RCA documentation. SCRs can be common types today and...
This two-door doorbell was found in a 1990s US publication. The circuit is still current as...
This sophisticated circuit using a liquid crystal display was found in Radio Electronics from the...