Hammond M2 repairs

[Greg Pretty]

I have one key that is only partially sounding: lower partials are missing. Any suggestions?

[Enzo]

Key contacts - dirty, oxidised, broken off, something. If that one has drawbars - I don't recall either way - clean them too.

[Rhodesplyr]

There are busbars that run under the manuals, and though they have palladium wire contacts, they can get dirty. Strike the key several times in rapid succession to see if the missing harmonics come back. If they don't, you may have broken wires inside the manual, which requires major disassembly to fix, or you may have dirty busbars that need cleaning. I've never done a busbar cleaning on an M-series organ, so I'm not sure if they come out the same way they do in the larger console organs.

If it were a drawbar problem, you'd have particular harmonics missing on multiple keys, but it's a good idea to spray them with DeOxit.

[Greg Pretty]

Hey that seemed to work!

Thanks for your comments. Being a drummer, this is all new to me. However after I gave the drawbars and the failing key a good exercise the harmonic came back! So that's good! I have also noticed that on the top manual, the four or five highest notes tend to drop off in volume. Maybe this is a characteristic of the instrument?? It appears that generally the lower you play (on either manual) the louder it gets. Is this typical?

Also I noticed that there was no "ratchet" feel to a lot of the drawbars, so I tried prying the metal contacts up so they were more arched. Was this a bad idea??? Would it be a good idea to take an emery cloth to the metal strips?

[Rhodesplyr]

I'd have to check the mapping of the tones to the keys to see if the volume drop on the higher notes is normal. I've never spent that much time playing on an M-series organ. Both The Hammond Forum and Hamtech mailing lists would be much better places to get expert answers on this topic.

The upper tones from the tone generator have series-resonant filters on them tuned to the desired frequency. Over time the paper capacitors used back then drift in value and increase in ESR, detuning the filters, making the organ considerably more rolled-off in the top end. Ideally, the value of the capacitor was matched to the the particular inductor, but replacing them all with 0.1uF capacitors will get you a lot closer to how it sounded when it left the factory. (A few lower tones use .22uF caps.) To peak each filter, you need values between ~0.090uF and 0.110uF Later organs used mylar capacitors that are less prone to drift. Worn tubes, etc... could also limit your high end, and remember that the M-2 has only a single speaker. You're not going to get the same highs you'll get from a Leslie's horn driver.

Around 1954, Hammond introduced "smooth" drawbars that have little ratchet feel, and Hammond players have spent a lot of time and money to get rid of the older ratchet drawbars and replace them with the smooth ones, so you're headed in the wrong direction! LOL.