Hammond M2 speaker wiring HELP!!!

[j_howell]

Got an early '50s M2 for free, with a nice, shiny reconed speaker. Awesome. Not awesome- no idea how to wire the speaker back in! I found a schematic, but it doesn't account for the later-added reverb...

[Freakmagnet451]

First of all, the M2 does not use a field-coil speaker like the M1 - correct? Depending on the reverb installation you may need two speakers. Many Hammonds had a second amplifier for the reverb. You need to make sure the output transformers of both amplifiers see a load (speaker) or they will overheat and fail. Just follow the output leads from the output transformers on the main amplifier and hook your speaker up to that. If there is an additional reverb amplifier do the same with it. If there is no room inside the box for another speaker, just run to an extension cabinet. In that case you might want to install a 1/4 jack on the amplifier chassis so you can use a standard phone plug to phone plug speaker cable to hook up any cabinet you would like to try. Take your time, double check your work and be prepared for the next steps - replacing dead capacitors and testing the tubes to make sure they are all working. Good luck!

[j_howell]

Yep, this one is field-coil, which is what's such a pain in my ass! I found a schematic (non-reverb), wired it that way, and still, nothing. The fella I got it from said it was not only working but it was kinda hot shit before he yanked the speaker to have it reconed (and didn't mark the wires!). I know that it did have a Leslie (which I unfortunately didn't get) when he got it...

So yeah, I dunno. A mutual friend of ours (the guy I got it from, that is), has an M3 that's a couple of years newer, and looks like the only real difference may be that it had the reverb in it stock, whereas my M2 had it added later as it wasn't invented yet when it was built. I'm gonna try (schedule permitting) to get down there, take a look at his, take photos or make diagrams, whatever...

But indeed, it does look as though the reverb has an amp of its own...perhaps the reverb only fed the Leslie? Ugh...

[Freakmagnet451]

I had a Hammond M1 that had a field coil speaker in it. It is 1000 miles away so I can't document the wiring but I am going to take a wild guess that the field coil is going to be higher impedance than the voice coil of the speaker.

So, hook the wires from the output transformer of the amplifier - identified as such by the wiring leading from the output tubes (6v6?) to the voice coil of the speaker. The wires going to the field coil will be coming from the power supply area of the amp, this current makes the electromagnet work.

Usually there is another amp inside the Leslie speaker. You can also google for instructions on converting an older field coil circuit to a more modern one ad use a modern speaker. This appears to be a fairly simple and inexpensive procedure.

[j_howell]

INteresting...I'll check it out. I think converting to a permanent-magnet speaker wouldn't be TOO hard; I think mostly it's an issue of finding an appropriate transformer. Maybe something roughly equivalent to what's in a Vibrolux or something would work?

[paully]

If your going to try to replace the field-coil speaker with a transformer and a regular speaker, take a look here.

http://captain-foldback.com/

At the bottom, click on Hammonds, then schematics, then find the M2 schematic. At the very bottom of the second file(the right side of the schematic), it states that on early M2s the field coil impedance is 1000 ohms. That should be a clue when you start trying to match up a transformer.

Best, Paul

[kickoldman]

incredibly, I just pulled an m series amplifier from a broken organ this morning! I'm interested in using it as a low wattage guitar power amp. I understand I'll need to supply a preamp fo it, but I'm defintely a novice at this. Can anyone clarify how one substitutes a "normal" speaker for the field coil normally used? Not gonna lie, field coils make me nervous.

[paully]

incredibly, I just pulled an m series amplifier from a broken organ this morning! I'm interested in using it as a low wattage guitar power amp. I understand I'll need to supply a preamp fo it, but I'm defintely a novice at this. Can anyone clarify how one substitutes a "normal" speaker for the field coil normally used? Not gonna lie, field coils make me nervous.

>>>>>>>>>>>>>>>
Well they should. This is a job that requires extreme caution. You're working around voltages in excess of 250VDC. That can kill you. To answer your questions, a field coil speaker takes the power needed to drive it directly from the amp supply, with no matching output transformer. Extremely high voltages are present at the speakers' lugs. A normal speaker can be substituted, but an output transformer with the proper I/O impedances and power rating must be inserted between the amps' output tubes and the speaker. Not a novices' job. Read this first:

http://www.tonewheelgeneral.com/index.p ... econe.html

Again, the organ amp that you pulled needs an output transformer with the proper load impedance added in order to mate up to a normal speaker.

Best, Paul

[kickoldman]

Thanks for the link! I'm not one to jump into projects without regard to safety. I've done some work on fender tube amps, but have never come across the field coil. Sort of a foreign concept to me. I'll exercise caution and keep you all posted on any progress I make.

[moogrock]

soooo...

glad i found this thread...

i was about to chop my m2 down...
and was wondering what i could do about the speaker...

is there a safe way of removing it and leaving it disconnected?

i have modded an output off of the volume pedal jack that i LOVE the sound of...

but i dont know anything about field coils...

i was going to see if i could do some sort of dummy load so i dont destroy the amp... but not have it hooked up to the speaker...

of if i could put the speaker in an ext cab/etc..

thoughts/etc?

[moogrock]

also how do i check and make sure it is a field coil?

[brianroth]

Field coils typically performed double-duty as both a choke in the filtering circuit of the amplifier's B+ supply, and to create the magnetic field for the loudspeaker.

Hence, you will need to substitute a filter choke into the power supply circuit if you convert the system to use a "new" speaker that has a permanent magnet.

Bri

[kickoldman]

Hi Brian,

in you opinion would it be insufficient to replace the field coil with a power resistor of appropriate ohms? That is what is suggested in this service bulletin from Hammond back in '66. http://www.dairiki.org/HammondWiki/TSB%2027

[paully]

also how do i check and make sure it is a field coil?

>>>>>>>>>>>>>>>>
Hold a piece or iron/steel, such as a screw driver next to the winding cover. If it has a magnet, it will attract the metal. That's a normel speaker. If it doesn't, it's probably a field-coil speaker. Also, a check with an ohmmeter should produce a much higher reading than a normal speaker. According to the schematic in the link that I posted earlier, that impedance is in the range of 1000 ohms.. much higher than the more common 4, 8, 16 and 32 ohm 'normal' speakers.

Paul

[brianroth]

Hi Brian,

in you opinion would it be insufficient to replace the field coil with a power resistor of appropriate ohms? That is what is suggested in this service bulletin from Hammond back in '66. http://www.dairiki.org/HammondWiki/TSB%2027

Swapping-in a power resistor is indeed an "old trick", although it may not provide as good filtering and regulation as the "choke" created by the field coil.

But, if Hammond "blessed" the mod, I guess it should be OK!

Bri