It's basically a Pierce Oscillator Circuit which works even with low-activity crystals.
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| Quartz Crystal Tester |
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| Quartz Crystal Tester - Schematic |
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| Quartz Crystal Tester - Inside view |
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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.
'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.
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.
This tester works in the range 455kHz to 20Mhz, with overtone crystals oscillating at their fundamental frequency.
It's basically a Pierce Oscillator Circuit which works even with low-activity crystals.
Salvaged RF Ammeter
Years ago, a 0.75A 'thermocouple heating element' was salvaged from a meterless BC-442 Antenna Relay Unit. Only recently was it taken out, to build an RF Ammeter for low-power rigs.
A junk-box 50Ω, 1mA FSD moving coil meter, with a bakelite housing, was also put to good use. It has graduations only upto 50% of its scale.
An aluminium baking tray was reworked to accept a couple of SO-239 sockets and the meter.
The unit was tested after completion of assembly and wiring.
A homebrew CW rig was loaded to get a reading of 0.75A on a Weston 1.5A RF Ammeter. The Weston was then replaced by the unit to be tested.
The meter pointer stood at exactly 50% of full scale, indicating that the graduated portion of the scale covered the full range of the thermocouple. Notwithstanding the non-linear output of the thermocouple and the unmarked meter scale, staying within the graduated portion of the scale would avoid damage to the element!
Related post: Adjustable RF Ammeter
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| Salvaged RF Ammeter |
An aluminium baking tray was reworked to accept a couple of SO-239 sockets and the meter.
The unit was tested after completion of assembly and wiring.
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| Thermocouple RF Ammeter - Schematic |
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| Salvaged RF Ammeter - Inside view |
The meter pointer stood at exactly 50% of full scale, indicating that the graduated portion of the scale covered the full range of the thermocouple. Notwithstanding the non-linear output of the thermocouple and the unmarked meter scale, staying within the graduated portion of the scale would avoid damage to the element!
Related post: Adjustable RF Ammeter
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