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

tonewheel.com has the schematics for building a universal Leslie adapter. It allows the use of pretty much any Leslie cabinet with a Hammond organ equipped with an 122 type (8000 series) control kit. The schematics have been designed in a modular form so you can select the building blocks necessary for your specific application.

The Hammond expression pedal seems to be a mystery to many players, especially those that are more used to playing on clone wheels, even though at least some of these model the original Hammond expression pedal behavior very closely. Many people seem to think that the expression pedal on a Hammond is only used to control the volume of the organ, but this is only part of its function, it also acts as a (passive, non-linear) equalizer (EQ). When the volume is low, higher frequencies are much more attenuated (reduced) than lower ones, leading to a much bass-heavy sound and less pronounced highs. The reverse is true when the expression pedal is put to full throttle (loudest volume), which results in a much brighter sound with relatively reduced bass content.

Thus, you can influence the character setting of the tone by opening or closing the expression pedal. This may lead to an undesired low volume when aiming for a more bass-heavy tone with les emphasized highs, but this can be counteracted by increasing the amplification. This may be accomplished by turning up the Leslie or other amplifier you may be using to amplify the Hammond. This may also make drive your amp into overdrive more easily, so you may need to find the right balance in the settings of the amp and the expression pedal to give you the desired tonal balance as well as a usable travel to adjust dynamics using the pedal.

Personally I like overdriving the Leslie to get a bit of growl, and this gets much easier with the Leslie on very loud, and playing the expression pedal at the low volume end, pushing the Leslie into a nice drive when increasing the volume on the expression pedal.

I’ve compiled a list from  information available on the internet that may help date a Hammond console (A-100, C3, B3, D-100, RT-3)

1958 – Vibrato line box changed from wood to metal

1960 – Side blocks change from wood to plastic

1961 – Pilot lamp added

1962 – Vibrato knob changed from smooth to ribbed (‘fluted’)

Mid-1962 – AO28 transformer colour change from silver to black

Spring 1964 –  Start of using red caps

1965 – Hammond script changed from small to large with new logo

1965 – Foam replaces felt

1965 – Introduction of R/C (resistor/capacitor) networks to tones 37-48 to reduce hum and crosstalk

1969 – Drawbar plastic knob style change to have engraved tones

Additional information can be gleaned from the components in the organ. Speakers (A-100 series) are usually stamped with a production date; the same applies for tubes / valves as well as capacitors.

Here’s some information I found on the tubes / valves in Hammond consoles (A100-series, D100-series, B3,  C3,  RT3)

A0-28 pre-amp:  6X4, 12AX7/ECC83, 12AU7/ECC82, 12BH7, 6AU6 (2), 6C4 (2x)

A0-35 reverb-amp: 6X4, 12AX7/ECC83, 12AU7/ECC82, 12BH7, 6AU6 (2), 6C4 (2x)

A0-44 reverb-amp: 6CA4/EZ81, 6GW8/ECL86(2x)

A0-39 power-amp: 5U4GB, 12AX7/ECC83,  6BQ5/EL84/6P14 (2x)

An inside look at a Hammond tone generator. Shows the oiling system that uses cotton wicks, and explains and demonstrates the workings of the tone wheels.

Here’s a video of the synchronous motor in my A-102 running, with audio.