572-B
The General Radio 572-B Microphone Hummer was introduced in Bulletin 936 (1935) and remained available through Catalog M (1951).
The Type 572-B is a low-power AC source for bridges where waveform and stability are not essential but battery power is important. Its an electro-mechanical device where an electro-magnet in series carbon button microphone act apon a tuned metal reed. The carbon microphone is mechanically attached to the tuned reed providing positive feedback sustaining the oscillation. A set of secondary windings supply two levels of output at 1 khz. The 572-B is used in the following Types, 650-A Impedance Bridge, 1631-A Inductance Bridge, and 1614-A Capacitance. Its interesting to note the Heath Company included the 572-B as the AC generator for their IB1 Impedance Bridge.
Specifications
- Frequency: 1 kHz ±10%
- Output Power: approximately 15 mW into a matching load with 4½ V supply
- Internal Output Impedance: 10 Ω and 300 Ω
- Power Supply: 4½ to 6 V
Links
Photos
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Button Microphone Close Up.
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Button Microphone Close Up.
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Technical Drawing
