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The PP-2088-A/U is a solid-state radio vibrator (“chopper”) that was developed for the German military (BWB) as a drop-in replacement for the mechanical vibrator as used in the military DY-88 power supply. The DY-88 powers the AN/GRC-9 HF transceiver, used by NATO from 1946 until the mid-Seventies.
This solid-state chopper is designed such that it can be used for all 3 DC-voltages that the DY-88 PSU can be set at: 6V, 12V and 24V DC.
It accomplishes this wide range of voltage tolerance by using the existing switched resistor networks already present in the DY-88. Those switched resistors originally were used to limit the current to the mechanical vibrator interrupter coil, for both series- as well as shunt vibrator mode. The PP-2088-A/U uses these resistors in a clever way to adjust the DC biases for the chopper, depending on set input voltage.
This solid-state chopper was developed by Telemit in the late Sixties.
This solid-state chopper works well, but it is not overly efficient. As a result, it has a large heatsink, to cool the two 2N3054 silicon power transistors. The poor efficiency (actually lower than the original mechanical vibrator) is inherent to the design; a transformer feedback-coupled 115 Hz oscillator that operates between class B and C. Keep in mind power MOSFETS did not exist yet around 1970; this device is based on power transistors. Such transistors still have a significant emitter-collector rest-voltage when in saturation, which results in losses radiated as heat.
But the device does the job well, and does not suffer wear like mechanical vibrators do. As such, this was a huge advantage for the military as the much longer life-span of the device simplified the logistics.
IMPORTANT: this solid-state vibrator was a custom development for the military DY-88 power supply. It will NOT work in any other military power supply, even if the original DY-88 mechanical vibrator would have worked in those other power supplies.
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