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AO-39 is the Hammond part number of the power amplifier used in the A-100 series of Hammond organs.


The input network of the AO-39 has a high-cut filter in it. This is reportedly to compensate for the lousy bass response of the built-in speakers. If you would like to brighten up your A-100, you can remove this filtering. (I'll fill in the details upon request) -- JeffDairiki

Appendix: AO-39 Parts List


 V1         12AX7
 V2, V3     6BQ5/EL84
 V4         5U4GB

Resistors (Resistors are 1/2 Watt, 10% unless specified)

 R1, R2     47K
 R3, R4     33K
 R5, R6     330
 R7         250 ohm trimpot
 R8, R9     10K  (* remove to defeat high-cut)
 (there is no R10 that I can find)
 R11, R12   100K
 R13        22K
 R14, R15   470K
 R16, R17   1.0K
 R18, R19   100K, 2 w
 R20, R21   220, 1w, 5%
 R22        100 ohm trimpot
 R23, R24   180
 R25        20K, 10 w
 R26        470, 1 w
 R27        200, 10 w
 R28        50, 10 w


 C1         0.1 (* remove to defeat high-cut)
 C2, C3     0.047, 400v
 C4, C5     100uF, 25v
 C6, C7     30uF, 450v
 C8, C9     30uF, 450v
 C10        0.1 (* remove to defeat high-cut)


 120vac 60hz  AO23279
 120vac 60hz  AO23281 (output transformer)

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