This circuit of 1965 documentation makes use of a tunnel diode to retard a pulse without distortion. The components are from the era.
This source, with slight variations, can be found in other articles in this section and on this...
The circuit shown in the figure was suggested by National Semiconductor in its 1994 Linear...
If you have an old cassette player or bought one from a junk shop, you can set up a small table...