Northern Hammond BC rescue

[pokey91]

Hey everyone,

I recovered my first Hammond today, a Northern Hammond BC with serial number N915. I live in Alberta, Canada, so it's a two-switch start and not one of the 1-switch wonders from Ontario, lucky me! I'd like to bring it back to as close to original mechanical and electrical condition as possible, along with perc and smooth drawbars to get the best of the B3.



I'm an amateur tinkerer and have worked on other EPs and tube amps but not a Hammond, so have been reading everything I can over here and hoping for your thoughts on a few initial things I found.

Backstory: this was a church find, they were not able to find the tone cabinet or Leslie anywhere (I did get the bass pedals luckily). As there was also no Leslie switch, I am inclined to think it had a tone cab at some point. So I will admit that I purchased this organ 'ear unheard', however I can say it was 100% worth the financial risk. I waited all week until just today to pick it up and made a pot roast for some friends who helped me carry that sucker into the basement. Nothing broke during transit, which is its own miracle considering how brutal the roads are up here.

Anyway, it starts and runs fine from what I can tell. I intend to wire a 1/4" jack based on the dairiki circuit this week sometime just to see what sounds it can make.

Firstly, can anyone tell me what I've really got? Based on the TGH Age List and N915 serial number, I'd date it around 1937-1940, but the Hammond serial number is 5107 (though I read that sn's don't really mean much outside of USA?). It seems like 1937 is probably the correct answer, but is there another number that will identify it?




So the scariest thing I discovered (and surely unbeknownst to the church), was that this organ almost caught fire. The power terminal board had some major charring under what looks like an inductor maybe? Or an old cap? But what's more insane is that the back cover actually burned right through about halfway into the wood! The fact that the nitrocellulose did not ignite is proving this thing is a survivor and worthy of a second life.



Matches up with the back cover:


Needless to say, I would like to figure out what caused this short and I could use some help on that. I'm not planning to power it on any further until that is addressed.

The next mystery is, there was a large, ~80lb. aluminum box sitting next to the swell pedal and after getting the housing off it turned out to be another Northern Electric amp, model R4045 A. The organ itself has a 4-pin male connector, but this amp has two 5-pin connectors on the back and could drive two speakers by the looks of it. I'm not well versed on all the cable pinouts yet, but would like to know what it's use was or if I need it!

*I will add photos of the R 4045 in the next post, hit the limit for this post.*

I guess my general plan of action is to just clean as much of the organ part by part as I can, replace preamp caps as necessary. This is going to be a long haul but I'm keen to get it up to quality playing condition sooner than later. Obviously will know more once I hear it, but I welcome any input, suggestions and feedback.


Matt

[nonreverb]

I've owned several Northern's. Here's the first task. Before you do anything else is check and replace AC wiring! These organs are a campfires just waiting to happen. Trust me, I've been there.

[pokey91]

A few more pics!

Rear view, pretty clean throughout! I'll try to get a shot of it but man, that cabling job on the TWG is practically military spec. So tidy!



Ok I think I answered my first question. Does this ink code on both manuals mean "1937, May 5?" or "1937, 55th day" aka Feb 24th? Something else?


Here's the aforementioned R 4045 A amplifier, serial N980. I can't find any information other than a post here by Johnny B3, but it refers to an R 4045-C which isn't exactly the same. Seems like people desire these as monoblocks for music listening. I don't want to overload this thread with off-topic things, but I'll take any info on it as well.



Last but not least, the 4-pin male plug attached to my BC. Is this a specific thing to the Northerns? What do I do with it?

[pokey91]

I've owned several Northern's. Here's the first task. Before you do anything else is check and replace AC wiring! These organs are a campfires just waiting to happen. Trust me, I've been there.

Yeah I can see why! Is there any specific reason why they spontaneously combust? Do I need to just replace and clean up the wiring, or is there a fundamental component issue that needs to be changed to prevent fire? The only schematics I could find were for a Northern D so I don't have one for the R4044 preamp yet.

[muckelroy]

Disclaimer: I am no expert on the Northern Hammonds - there are others who are. However, assuming that this is laid out in a similar fashion as its USA brethren, the thing which burned is a resistor, whose purpose is to slow down the start motor during the moments that both start and run switches are being held on together.

Hammond run switches are actually two switches in one enclosure. One switch is "normally closed", and shorts together this power resistor, to thus send full AC power to the start motors. When you hit the run switch, that "normally closed" contact opens, which "adds" this resistor to the chain, and thus lowers the voltage being sent to the start motors, and slows them down slightly.

So, those 5 or so seconds of the start sequence are the only time that this resistor should ever conduct, or dissipate heat. In other words, the only time the resistor should do any conducting is when both the start switch is on, and the run switch is on, thus opening the "normally closed" contact of the run switch which adds this resistor in to slow down the start motors a bit. The fact that it burned, and burned everything around it so thoroughly, means that it got hot, and stayed hot for a quite long time (several minutes? hours? days? not sure.) It's not harmful for the resistor to "short" to itself, because most of the time while motors are being started w/ the start switch, that is exactly what the "normally closed" run switch is doing. However, the fact that it burned up so spectacularly may mean it simply failed due to age, or may mean that it was dropping way more voltage than it should have, and thus dissipating way more current than it should have.

At this point, you should replace the terminal strip, all the switch and power wiring, and the start and run switches. Best not leave anything to doubt. A lot of this wiring may look OK on the outside with cloth insulation, but it has a sort of rubber inner insulation that is cracked, or at very least, extremely hard and brittle. When you start tugging on a wire to replace wires, you may inevitably "crack" or break the insulation inside nearby or adjacent wires. That is to say, the two runs of stranded AC cloth wire that run to each of the two start motors, need special attention here. Those are very long runs of very long, brittle wiring that would be worthwhile to replace. It's not particularly easy to do, though, unless the generators are out on a table.

Some would argue that this resistor (and therefore the "normally closed" contact of the run switch) is un-necessary. The late Steve Leigh was one such person. I've not dabbled with his theory, but in practice, they seem to start fine without the start motor slowdowns at the end.

[Sweet Pete]

Congrats on your new acquisition! What church? Probably know it. I have BC N203 and it is a 1937 built in Montreal like yours.
It became BCV 5069 in 1950 or so.Field added kit.
An important disclaimer,mine was in almost perfect working order,had only to replace AC wiring AND a run motor for the chorus generator.
Recapped the TWG filters with mil-spec
Russian K42 types.Paper in oil just like the originals.In the process of adding a breakout box to replace the cables that just thread out of the wood.
Great sounding organs.The cabinets are from Quebec,made by Vilas up here.Darkest walnut I've ever seen on a Hammond.
It now has smooth playing keys and is comfortable to play.
Every playing key has been weight measured with a stack of 13 nickels,same weight as I took them out at.
Check your down weights,should be about 13 grams.Lots of science projects under those old keys,found two coins.1937 quarter and 1941 dime.
Dimes of that era were zinc....'tombaks',silver found a new application.

Look up Carl Mal up there for some help with that thing.

I am a "Legend of the Edmonton music scene",according the the CJSR Shoebox? Greetings from Vancouver!
cheers,
Pete

[David Anderson]

Others have covered the AC wiring issues and the fact that the large wirewound resistor should not stay powered long enough to burn anything.

Another thing to be aware of since you seem to be new to Hammonds is that the organ's internal preamp gets its high voltage (B+) supply from the power amp through the connecting cable, so even if you get the organ itself running, you will get no sound from the organ without an external high voltage power supply. This was true of all Hammond Organs through 1949. There are places that sell aftermarket power supplies for these.

Yes, the organ had to have an external tone cabinet since it had no internal power amp or speakers -- and certainly no room for anything like that inside a BC.

The Hammond amps I've dealt with from this period use a pair of 12" field-coil speakers, meaning that they had no adequate permanent magnets at this point and instead used speakers with large electromagnetic coils on the back, powered by DC current from the amp. It's a dissimilar pair of speakers with one 5k coil and one 250Ω coil. One used a 5-pin plug and the other, a 6-pin plug. If these are missing, it's more than simply finding replacement speakers because the field-coil electromagnets are an integral part of the amplifier design. The amps will not function without these field coils -- or some replacement -- plugged in.

I would familiarize yourself thoroughly with the circuits before you dive in. Some electronic components from the 1930s do not look like their later counterparts.

You've got a large learning curve to climb before you start thinking about smooth drawbars and percussion. There's a lot about these early Hammond consoles that's not at all like what you would find in an average guitar amp, and if you don't understand it, you risk getting into trouble. Even Hammond techs familiar with later 3-series organs and Leslie cabinets can get confused by the idiosyncrasies of these early models.

[pokey91]

The fact that it burned, and burned everything around it so thoroughly, means that it got hot, and stayed hot for a quite long time (several minutes? hours? days? not sure.)

Ok that is probably exactly what happened... when I picked up the organ, I noticed that both Start and Run switches were flipped on. So this may have even happened recently. The lady who sold it to me said they "didn't know how to turn it on but could hear sounds inside." So I guess it's a distinct possibility this happened recently. I will replace all those components.

Pete, thanks for the info! Sounds like our organs are distant siblings. I picked it up from a Seventh Day Adventist church off 95 st. but they had only purchased the church in 1999; the church itself has to be over 100 years old - not sure who the previous tenant was. That's why info from the seller was scarce. PS I'll check out your CJSR show this week!

David, thanks as well for the information. As I'm in no rush whatsoever, I'm happy to take the time to learn about this model for safe maintenance. I think you have explained why the unit came with that R 4045 A power amp, that would interface with perhaps the 4-pin male/ 2-prong female AC breakout box near the swell pedal? (See photos above). Here's a photo of the available connections on that power amp, it has a 5-pin female and two-prong AC both male and female per side.

And once again, the photo of the breakout box under my organ:



I haven't seen anything like this in any photos I've come across, although there was mention of it in this thread I found about field coil speakers, sounds like maybe it was a treble hookup to a field coil? I'm fuzzy on this so I'm doing my research!

Thanks all for your input so far, I'm a willing student and this seems to be a very knowledgable and helpful community.

Matt

[Drawbar Dave]

Welcome to the BC club! I own a UK 235 volt 50HZ model from 1937. Once you have sorted out the AC wiring issues, you can tap into the Rheostat box and get a passive signal to send to a guitar amp so that you can check that all the tones are present on the generator. Forum member tpappano recently went through a restoration on his BC as well.

[Joey_Gleet]

Congratulations. It will be good to follow your progress.

[David Anderson]

I live in the American Southeast, so I've never actually laid eyes on a Northern Hammond in real life, as far as I can remember. They tend not to end up down here. I don't know what that breakout box on the organ is, nor can I tell you what the connector arrangement on the amp panel is. At a certain point -- and I've had to do this many times -- you just have to get in there and trace the wires to figure out what something is for. In other words, the wires to the primary of the power transformer in the power amp will be the main AC wires. The signal wires to the driver tubes will be the balanced line inputs. The ground connection will be the shared ground. The wires from the output transformer secondaries will go the speaker connectors.

A full organ to power amp connection for a Hammond BC takes 6 pins: two for balanced line audio, one for ground, one for B+ voltage, and two for AC mains. You would usually find a 6-pin male plug on the power amp, but I don't see one in your photos.

You don't find those recessed AC plug connections or AC sockets on standard U.S. Hammond tone cabinet power amps, so unless someone could identify this as some kind of known Northern Hammond configuration, I would have to start doing detective work under the chassis. You do occasionally run into situations where someone has cobbled together their own custom hookup arrangement. It will be interesting to see what all this turns out to be. I've been working on Hammonds and Leslies for almost 30 years, and I've never seen anything exactly like what you have pictured here.

Edit: Looking at the schematic posted for these Northern Electric amps, there isn't much to them. No driver tubes. They appear to use interstage transformers to drive the output tubes, which was not too uncommon back then. Kind of looks like they used separate cables for AC power rather than a 6-pin cable. There's an 8-pin connector that has audio and B+/Ground on it.

Those amps use one 5-pin plug for both field-coil speakers. One looks like a 5k coil, but the other value was hard to read.

[tpappano]

It looks like two different resistance field coils are in series from B+ to ground, acting as a voltage divider to derive screen voltage for the 6L6s. The speakers must have been different sizes, woofer-tweeter maybe? Seems like resistors could be substituted to use pm speakers

[David Anderson]

I agree with your reading of the circuit, and that confirms that the amp won't work without the field coils or something in their place. You can substitute wirewound resistors of sufficient wattage. On the linked schematic of the amp, I could read that one coil was 5,000 Ohms, but I couldn't quite make out the other. It's something like 1,360 or 1,860. On all the early Hammond Tone Cabinets of the 1930s and 40s, they had two identical 12" Jensen A12 speakers. That was it. There's no crossover or use of bass and treble channels. All that came later.

Of course, any Leslie from the 6H family or a later complete Hammond Tone Cabinet would power the preamp and render amp retrofitting unnecessary. As it is, he'd had to buy speakers, put them in some kind of cabinet, and rig up resistor replacements for the field-coils. The field coils dissipated as much as 14-15W, so it can take large resistors that have to be located where they don't turn the amp into an oven.

[tpappano]

Congratulations on your new BC! You have definitely come to the right place for all the help and info to get it running! Like Dave mentioned above, I completely overhauled mine and it sounds awesome. The organ itself is a pretty straightforward design, containing multiples of relatively simple (but elegant) mechanisms (tonewheels) and switching circuits (keys, presets) Some of the restoration work can be tedious and time consuming, but not really difficult. For example, I removed both tone generators to work on them. Only took two hours to get them out, but ten to put them back in 8) I wouldn't worry about putting in ‘smooth' drawbars until you have everything working, you might decide the originals are fine. Anyway, it's only a one or two hour job to put them in If you decide to. You will get a great deal of satisfaction from getting her running and sounding like new!

[David Anderson]

After thinking about it, I think this is probably how this organ/amp situation is set up. The breakout box on the organ provides switched AC power to the power amps, either directly from the Run switch or via a relay, connected to the breakout box with a 4-pin plug and cable (now missing?) from the organ's line panel -- even if all 4 pins aren't used. AC power goes to the power amps via the typical Hammond power cord of the era with a round female end into the round male socket on the first amp and is then daisy-chained to the second amp using the standard electrical outlet on the first amp. Unlike typical Hammond setups, AC power does not run in the same cable as the audio and other connections.

Balanced line audio and Ground/B+ are connected via some (also presumably now missing) cable from the organ to 8-pin sockets on the power amp chassis. As with AC power, the second amp is daisy-chained to the first. (B+ should probably be connected only at the first amp.)

Two 12" Jensen FC speakers plug into the 5-pin socket of each power amp via some kind of harness for a total of four 12" speakers. The speakers' cones and voice coils would be the same, but within each pair connected to one amp, there would be two different field coil DC resistances.

This raises the question: With all the speakers and the actual cabinet missing, how does the OP want to proceed? Any 6H Leslie or standard Hammond Tone Cabinet will work, provide B+ voltage to the preamp, and eliminate the problem of the lack of the original speakers and the speaker enclosure.

[tpappano]

You could probably sell those amps to a collector or cult member for enough to almost cover the cost of a Leslie 8) I agree with David, it would be a lot less hassle to just get a conventional Hammond or Leslie speaker. A lot to be said for having speakers already in a box ready to play.

If "decor" is not an issue, you can have some real inexpensive fun with used PA cabinets and an appropriate amp. I found a pair of 15" cabs for $10 each and hooked them up to a 300 watt Crown amp. Ask my neighbors what *that* sounds like!

[pokey91]

Thanks for all the input guys. Had a busier week than I hoped so I'll have to dig more into it next week. David I believe you're right in regards to the power amp setup with the FCs, and yes sadly that 4-pin cable is no longer with the organ. I tried to open up the breakout box this week quickly but the AC and 4-pin socket wires were too tight to open without tearing the leads off so I'll look for another way in, or just extend them. I'd like to get t he AC swapped out in the next few weeks.

so just to be clear, any 6H Leslie (122 etc) would be able to supply the B+ and theoretically eliminate the need for the external power amp? I may go that route, I haven't got the time to be building speaker cabs as much as I'd like, and I think I might know where I can find a 122 even! Not in a huge rush at this point.