Audio Signal Injector

This decades-old audio signal injector was wired on a piece of perfboard.  All components were sourced from the junk box.

Audio Signal Injector

The enclosure was fashioned from an empty tapered spool of industrial sewing thread, a cosmetic tube cap and a film canister cap on which the push button switch was fixed.

A machine screw, filed to a point and fixed to the cosmetic tube cap, served as the prod.

Audio Signal Injector - Schematic

Over the years, this unit has helped service the audio stages of several ham rigs.

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Quartz Crystal Tester

This unit was built years ago when there was a need to test surplus crystals. It also came in handy as a signal generator for receiver alignment.

It's basically a Pierce Oscillator Circuit which works even with low-activity crystals.

Quartz Crystal Tester

'Octal' and '807' valve bases were wired for vintage crystals in addition to crystal holders suitable for HC-6/U, HC-18/U & HC-25/U crystals.

Quartz Crystal Tester - Schematic

The indicator is a 6V 0.06A dial lamp. Tuning / Loading is done using the PVC-2J 500+500 pf variable. The 2000 pf is switched in parallel for very low frequencies.

Quartz Crystal Tester - Inside view

This tester works in the range 455kHz to 20Mhz, with overtone crystals oscillating at their fundamental frequency.

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