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.