The guys from Green Bay Professional Packet Radio have an excellent page on homebrewing the Kaiser 1059 preamplifier.
For those of you who are wondering what the heck this is, it’s an extremely versatile low noise amplifier which is a true classic of technical surveillance countermeasures (TSCM) work… in other words, a bug-hunters’ favorite toy.
One of the neat parts about this amplifier is that it has four (!) inputs. This means that no matter what the audio source is, the 1059 can probably handle it — just about any microphone will work with the 1059, and if you encounter an unknown line you can clip in the 1059 and check to see if the line carries audio.
Why is this important? Well, any bug sweep has to look at every possible way of getting the signal outside a given area, including both in-us and disused wiring pairs. If the amplifier you hook up to check a line is a poor match, you may miss a faint signal…
Bonus: the page also includes schematics and home-brew writeups for many other pieces of iconic Kaiser gear, and even links to his rare public talk on TSCM at the Last HOPE.