Hammond M2 speaker wiring HELP!!!

[moogrock]

also..
what about the slate and red lead going to the voice coil in the feildcoil wiring diagram?
is this a ground?

again, thanks.

[brianroth]

soooo...

the "dog bone" serves basically as a field coil?

then do i still need to attach a dummy 8ohm load in lieu of a speaker?

sorry i am asking so many questions... there is just a completely new concept to me and i do NOT want to injure my precious precious organ...
and all of the info i can find on the internet about this assumes that you know a lot about this system already...
which obviously i do not...

thanks again and again.

Yes, the dog bone becomes a replacement fot the field coil.

I had originally toyed with the idea if "yanking out" the output tubes in the amplifier, but dumped that idea. Instead, drop an 8 Ohm dummy load across the output of the amplifier which will substitute for the "missing" 8 Ohm loudspeaker.

[brianroth]

also..
what about the slate and red lead going to the voice coil in the feildcoil wiring diagram?
is this a ground?

again, thanks.

How many wires are going to the Hammond speaker, and what are the color codes?

Bri

[paully]

Brian, the resistor sub should work, but a suitable inductor should be available here. I don't know the power requirements, so I didn't look past the required impedance. Mouser doesn't show their full line. http://store.cd4power.com/cgi-bin/cd4po ... talog/1024 BTW, the Leslie 122 filter choke didn't spec out in impedance.

Too bad there aren't 2 seperate threads, as 2 different things are being discussed here. I'd like to address the line-out solution. The RCA jack found in these models works for some, while others have problems. What it doesn't do is remove the organ's internal speaker when it's used. We used to use the circuit below to install reverbs into M3 and B3s, but the same procedure works fine for routing the signal out of the organ, while removing the internal speaker at the same time.

http://i125.photobucket.com/albums/p71/ ... switch.jpg

The nice part was that a socket adapter was available(and still is) that let you remove the 12ax7, install the adapter, then re-install the tube with no cutting or soldering. It looked like this:

http://i125.photobucket.com/albums/p71/ ... dapter.jpg

Unfortunately the M2 uses a 6sc7 tube at this spot(V4), and I couldn't find one of these adapters for it's base.

http://i125.photobucket.com/albums/p71/ ... ockets.jpg

If anyone knows of a source for these adapters, please advise. They're invaluable. TREK II has the ones for the 12ax7
http://www.trekii.com/#RV1C . The 'tube interface socket' is available seperately.

Best, Paul

[moogrock]

yeah...
the two threads wrapped into one are a little confusing...

but...

i am going to pull the speaker or move the organ to get a better look at the color codes / etc...

the green & black are there... as well as what appears to be a red and a black... but it looks like two other lines... that have been repaired... so its hard to check...

i am going to try to move the organ so i can get a better look sometime this weekend...

mine is actually an M3 not an M2.
i am going to chop it down... so removing the speaker/etc is something i need to do... to lessen the weight/etc...

thanks so much.

[blakbeltjonez]

That is definitely a field coil speaker in the pix you posted. (I collect antique radios hehhe).

Hmmmm...my first thought was to suggest yanking the output tubes from the amplifier to disable the drive to the speaker. BUT, that will likely cause the B+ voltage to soar. So, if you want to totally ditch the speaker, wire an 8-ish Ohm set of "dummy load" resistors in place of the speaker's voice coil.

An earlier posting in this thread linked to a 1960's Hammond service bulletin which recommended a 750 or 1000 Ohm (depending on serial number), 20 Watt resistor as a substitution for the field coil. That will keep the amplifier running. The resistor will need to be carefully mounted within the chassis so that the heat it produces won't melt something else in the vicinity.

Bri

having no load for the field coil portion of the amp will definitely cause problems - our shop just had an old amp in for service where i work (which deals almost exclusively with old Hammond repair/restoration) with exactly the scenario described above. a very healthy 20+ watt loading resistor needs to be in place, and the resistor needs to be roughly the same as the impedance of the field coil (i believe they range from about 1K-2Kohm depending on the model of field coil speaker, quite a bit more than a standard speaker).

[brianroth]

yeah...
the two threads wrapped into one are a little confusing...

but...

i am going to pull the speaker or move the organ to get a better look at the color codes / etc...

the green & black are there... as well as what appears to be a red and a black... but it looks like two other lines... that have been repaired... so its hard to check...

i am going to try to move the organ so i can get a better look sometime this weekend...

mine is actually an M3 not an M2.
i am going to chop it down... so removing the speaker/etc is something i need to do... to lessen the weight/etc...

thanks so much.

OK,..I downloaded the M3 schematic and I see there should be four wires heading to the loudspeaker, terminated onto some sort of 5 pin connector.

The field coil resistance is listed at 700 Ohms, with 100 Volts across it. That calculates to approx 14.3 Watts, so a 25 W dog bone is a good solution, along with an 8 Ohm dummy load for the voice coil. I would think both resistors could be stashed in/on the chassis, and wired to the 5-pin speaker connector.

For a line level audio output, you would only need to parallel a pad across the 8 Ohm dummy load. You'll end up with a nifty Low-Z, transformer isolated output that (potentially) will include any "growl" that the push-pull 6V6 output stage might provide.

The basic idea is, in effect, a "hot plate", like used with guitar amps.

Bri

[brianroth]

having no load for the field coil portion of the amp will definitely cause problems - our shop just had an old amp in for service where i work (which deals almost exclusively with old Hammond repair/restoration) with exactly the scenario described above. a very healthy 20+ watt loading resistor needs to be in place, and the resistor needs to be roughly the same as the impedance of the field coil (i believe they range from about 1K-2Kohm depending on the model of field coil speaker, quite a bit more than a standard speaker).

The field coil is an INTEGRAL part of the power supply, and acts as a filter choke. Without the field coil (or a substitute), the power supply cannot function.

In the Hammond designs, the field coil is in the ground-return portion of the power supply, which means that the voltages across the field will be lower compared to the more "conventional" connection of a filter choke in the main B+ line.

Nevertheless, Volts are Volts and Ohms are Ohms and Watts are Watts. In this case, just over 14 Watts will be dissipated by a 700 Ohm resistor "substitute" for the field coil. This resistor will run HOT, and needs to be carefully placed/mounted on the chassis.

I still haven't found a "catalog item" filter choke with 700 Ohms series resistance and a current rating of 143 mA (later value calculated by I = E/R, or 100/700).

None of this, however, has anything to do with the voice coil of the speaker, which is shown as a standard 8 Ohms in all the schematics I've been looking at.

There are two independent circuits in-play here....the field coil which supplies the electromagnetic field for the speaker as well as some "choke filtering" for the power supply, and the voice coil itself which moves within the magnetic field created by the field coil. (More modern speakers have only the voice coil and a permanent magnet vs. an electromagnet).

Bri

.

[j_howell]

...great info all the way around, but not exactly what I need. If someone could snap pics, draw a diagram, or even just describe the connections (color codes especially!) of the wiring from the amp to the reverb to the speaker (this wire comes from here, goes to there, that sort of thing), I'd be eternally grateful!

Gracias!

[paully]

...great info all the way around, but not exactly what I need. If someone could snap pics, draw a diagram, or even just describe the connections (color codes especially!) of the wiring from the amp to the reverb to the speaker (this wire comes from here, goes to there, that sort of thing), I'd be eternally grateful! Gracias!

>>>>>>>>>>>>>>
Actually the color coding for the FC speakers was covered by Brian earlier. Take a look at the post and see if anything looks familiar. Also mentioned earlier, the reverb is either a stand-alone unit with it's own amp and speaker(is there another speaker anywhere?), or a retrofit which becomes part of the preamp circuit and is not a factor with the speaker wires. It's really incumbant on you to snap some pics of the wires(how many) that you're looking at, what color they are, and where they are currently attached. A pic of the speaker would help. As for the reverb, they weren't included with the schematic because this was an option, not part of the assembly line product. At least I couldn't find paper with a reverb included. FWIW, I found a diagram for a stand-alone reverb unit(Leslie installed). It does take it's signal from the main amp, which may be the extra wires if indeed there are extra wires. http://theatreorgans.com/hammond/faq/fi ... 22vb-a.pdf

In general, and according to the old schematics, you shouldn't be looking at more than 4 wires to the speaker for an M2. How many are actually dangling? Do a little nosing around inside and post up what you find.

Best, Paul

[brianroth]

I try to help as best as I can, but often it's just "trolling" through piles of Olde Docs to find snippets of info... especially if I don't have an actual unit at-hand to personally inspect.

Hence, I try to dig up the info, but I cannot always suggest "hook THIS to HERE" in a definite fashion.

I've ...ahhh..MUCKED with enough of this gear for long enough to develop my own processes for any of the machines, but my repairs/mods/suggestions are typically developed "on the fly" once I've dived into the machine in question....and also have "dived" inside that machine within the past decade or two...LOL!!

"Give a man a fish, he eats one meal. Teach a man to fish, he's set forever"...or some-such paraphrase.

Bri (I have good intentions, but cannot recall every nuance about every machine)

[j_howell]

Your help is much appreciated! Thanks!

It's a little tricky all the way around...I think mostly the issue with my M2 is that the reverb was added later (as it hadn't been invented yet when the organ was built!). I'd tried to find info but had a hard time...essentially, near as I can tell, with the added reverb unit, it's basically just upgraded to an M3, more or less, but I could be wrong...and then there's that it had a Leslie, the controls for it are still attached, but I don't have the Lelslie. I don't think that'd be an issue, as the Leslie should've had its own internal amp, but...I dunno. Organs are not my specialty- I'm just trying to get this one going, so it serves a purpose besides being a massivem heavy space-taker-upper. We'll see how that develops!

Thanks!

[brianroth]

Again, if you want to delete the main speaker, trace the wiring color codes FROM the speaker to see if anything matches with the old RETMA color scheme.

Bri