paully wrote:Paul
impedance is 8 Ohms, and NOT 1000 Ohms. 1000 Ohms is the resistance of the field coil itself.Bri[/quote]
>>>>>>>>>>>>>>
OOPS
. Good catch, Brian. It's been 30 years since I actually replaced one of those things. Should have looked at the paper more closely. To correct what I said earlier, that 1000 ohm measurement doesn't apply to the actual speaker, so it's not a way to ID a regular speaker from a field coil speaker. The passive magnetism check with a screwdriver should still provide a clue, as well as the extra terminals.
FWIW, if the choke was replaced with a regular choke of the same value to maintain the overall operating voltages, and an 8 ohm speaker with a permanent magnet was installed, wouldn't that work for the M2? (OMG, I'm back in class
)
Best, Paul[/quote]
The physical construction seen in the pix posted clearly shows it is a field coil speaker....the "winding bobbin" is visible, versus a permanent magnet.
Somewhere I have a chart of the "standard" color coding for the wiring to a field coil speaker, assuming that Hammond's stuff followed the color code.
IF someone wanted to replace the speaker with a "modern" permanent magnet speaker, a vanilla 8 Ohm speaker would work just fine...IF the field coil issue was dealt with.
The field coil is indeed part of the power supply circuit, acting as a filter choke in addition to supplying the magnetic field for the speaker itself. The Hammond service bulletin linked in an earlier message in this thread suggests a 20 Watt resistor as a suitable replacement for the field coil.
A filter choke would perhaps be a better solution. Hmmmm....750 or 1000 Ohms at 100 mA. Triad and Hammond Manufacturing (no relation to "Hammond Organs") are the only remaining makers of chokes that I know of, at least as catalog items. No luck with either.
OK, so be it. Hammond Organ's service bulletin "blessed" a 20 W resistor as a sub for the field coil. There's the answer.
Bri
PS, I am a HUGE fan of Hammonds. Buy a tube of oil to keep the gearbox happy.
My current studio install project includes a PRIMO-condition B3 and a 122 Leslie as part of the gear in the tracking room. Ohhhhh yess!!!! Smoke On The Water... lol!! The growl of a B3 and 122 with the "expression pedal' mashed to the floor is part-and-parcel of the sound of rock and roll. Or, if you perfer your Hammond/Leslie combo to be a tad less distorted, "Green Eyed Lady" by Sugarloaf is the consumate Old Skool rock song with Hammond all over the place. And, let's not forget Booker T. and the MGs.
PPS, Back In Ye Olde Daze (1970's), the keyboard player in a local band owned a Hammond "A", which had a tag stating it was built by the Hammond Clock Company. Great info here about Hammond Clock, etc:
http://thehammondorganstory.com/
Hammonds kick butt.....and the gearbox, drawbars, etc. are a testament to Old Fashioned American Ingenuity. Don't get me started <g>. Uh..oh..."start" "run" switches hahahha. I can hear the gearbox turning as I type this....and it's a marvelous sound.
