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AO-28 is the model number of the pre-amplifier used in the B-3, C-3, ?RT-3, as well as the A-100 and ?D-100 series HammondOrgans.

Upside-Down AO-28s?

The AO-28's in A-100's are mounted upside-down. To convert an AO-28 between rightside-up and upside-down operation (or vice versa), two wires going to the swell capacitor must be swapped. A photograph detailing the wires to be swapped is available at (courtesy of ?PeterAbrams.)

External Links

Frequency Response

See AO-28 Frequency Response for plots of the frequency response of an actual AO-28, as measured by BradBaker.

Parts List

?DennisWage has written up a parts list (complete with MouserElectronics part numbers). You can find it at

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