Schematic and parts list of the Hammond Preamp AO-28 (B3, C3)

Schematic of Hammond Preamp AO-28 Schematic of Hammond Preamp AO-28

AO-28 Capacitors

AmountCapacityTypeVoltageSchematic Nr.Mouser Part Nr.
125/25VElectrolytic25VC3075-TVA1205
230/25VElectrolytic25VC9, C2675-TVA1412
110/350VElectrolytic350VC5975-TVA1705
130/350VElectrolytic350VC5875-TVA1907
140/400VElectrolytic400VC5775-TVA1712
140/450VElectrolytic450VC5675-TVA1712
150/300VElectrolytic300VC6075-TVA1713
3100PFceramic500VC3,C8,C295982-15-500V100
1150PFceramic500VC355982-10-500V150
2220PFceramic500VC18, C205982-10-500V220
124PFceramic500VC75982-10-500V24
130PFceramic500VC65982-15-500V30
1390PFceramic500VC32**, C35*5982-15-500V390
139PFceramic500VC25982-15-500V39
151PFceramic500VC155982-15-500V50
1680PFceramic500VC175982-19-500V680
182PFceramic500VC245982-15-500V82
10.0015uFceramic500VC3475-715P600V0.0015
30.001uFceramic500VC25,C21,C3475-715P600V0.001
20.0022uFceramic500VC19,C33*75-715P600V0.0022
10.0033uFceramic500VC33**75-715P600V0.0033
20.0047uFFILM100VC11, C1275-715P600V0.0047
10.0082uFFILM1000VC3275-5GAD82
10.01uFFILM200VC575-715P200V0.01
20.033uFFILM400VC23,C1675-715P400V0.033
10.047uFFILM400VC2875-715P400V0.047
30.33uFFILM200VC4,C10,C3175-715P200V0.33
11.0uFFILM200VC1375-710P105X9400

AO-28 Resistors

AmountResistanceWattageTypeSubtypeSchematic Nr.Mouser part Nr.
647K0.5WMetalFilmR6,R16,R47,R52*,R53*,R54*273-47K-RC
21.2K0.5WCarbonComp.R42,R1730BJ500-1.2K
11.5M0.5WCarbonComp.R5730BJ500-1.5M
41.8M0.5WCarbonFilmR30,R32,R27,R4293-1.8M-RC
2100K0.5WMetalFilmR41,R62**273-100K-RC
1100 Ohms0.5WCarbonComp.R2530BJ500-100
310M0.25WCarbonFilmR5,R14,R18291-10M-RC
115M0.25WCarbonFilmR34291-15M-RC
11M0.5WMetalFilmR21273-1.0M-RC
12.2K0.5WCarbonComp.R4930BJ500-2.2K
22.2M0.5WCarbonComp.R7,R2030BJ500-2.2M
12.7M0.5WCarbonFilmR15293-2.7M-RC
1220K0.5WMetalFilmR62273-220K
122K0.5WCarbonComp.R5630BJ500-22K
122 Ohms0.5WCarbonComp.R5030BJ500-22
3270K0.5WMetalFilmR37,R3,R12273-270K-RC
13.3M0.5WCarbonFilmR35293-3.3M-RC
13.9M was 6.8M0.5WCarbonFilmR10293-6.8M-RC
2330K0.5WCarbonComp.R36,R2930BJ500-330K
1330K0.5WMetalFilmR39273-330K-RC
2390K0.5WMetalFilmR38,R63273-390K-RC
139K0.5WMetalFilmR61273-39K-RC
14.7K0.5WCarbonComp.R5130BJ500-4.7K
14.7M0.5WCarbonFilmR13293-4.7M-RC
14.7M0.5WCarbonComp.R5830BJ500-4.7M
2470K0.5WCarbonComp.R8,R1930BJ500-470K
1470K0.5WMetalFilmR48273-470K-RC
647K0.5WMetalFilmR6,R16,R47,R52*,R53*,R54*273-47K-RC
268K0.5WMetalFilmR31, R33273-68K-RC
1820K0.5WMetalFilmR9273-820K-RC
1820 Ohms0.5WCarbonComp.R2230BJ500-820
182K0.5WCarbonComp.R5530BJ500-82K
222K1WCeramicComp.R23, R24588-OX-22K
1180 Ohms5WCementR99280-CR5-180
22.7K5WCementR100, R101280-CR5-2.7K
34700 Ohms5WCementR94, R95, R96280-CR5-4.7K
1900 Ohms10WCementR91280-CR10-910
17500 Ohms10WCementR98280-CR10-5.0K

* These components are for AO-28-1 amplifiers with no code letter only
** These components are for H-AO-28-5 amplifiers

Leslie 122RV Pictures

Here’s some pictures I took of my Leslie 122 RV. From what I could find on  this model I understand that they usually come with a Leslie-designed reverb amp which is not deemed all that desirable, but this one actually has a Hammond AO-44-1 reverb amp in it, the very same as is found in the A-100 series. I think it sounds great, even through the small speaker that is mounted on the side of the cabinet.

Leslie 122 Amp
Leslie 122 Amp
Potentiometer for Leslie 122RV Hammond Reverb Amp

Restored Hammond Service Manual available

A post on the organ forum  provides for the download location of a newly restored version of the Hammond Organ Service Manual for free download, painstakingly put together by Organ Forum member Joey B3.

The new version has been completely re-typeset, some pictures have been replaced with better versions, and some sections and some diagrams / schematics have been reintroduced from earlier manuals that were not included in version 495 from sources such as the original 1936-1944, as well as some manuals from the “pre B3” 50s.

The diagrams/schematics/charts have been scanned in at 600dpi for maximum clarity when zooming in. The scans were taken directly from original manuals of the 50s and 60s, with the exception of the diagrams for the Model E and C2-G. It is available as PDF, bookmarked per chapter. It is a more accessible, cleaner version than the one all over the Internet now and should be very useful to anyone who does not have access to an original.

Covers the following Hammond organs: A, A100, AB, BC, BCV, BV, B2, B3, C, CV, C2, C2-G, C3, D, DV, D100, E, G, GV, RT, RT2, and RT3