Rodgers 750B help

[ns9987]

Well I finally was able to get an AGO spec organ to be used as a home practice instrument. My 1973 Hammond T-582C has been broken for many years now, and all I have been able to practice on is a 61-key casio keyboard... Well... All that is in the past now!! A dear friend sent me the link for a FREE Rodgers 750B organ for sale online. I just had to drive a good distance to get it was all, but Free is Free! When I got to the church to get it some church members had already taken the pedals off of it... and all I got to play was the manuals... I liked the tone this organ right off the bat!! I didn't get to try every stop but the few I selected seemed to play and sound pretty decent... I thought... For Free... this is a dream come true for myself!! So it took 8 large men to pick the organ up and get it out of their church's choir recess in the floor... The men then used a set of organ dollies I rented just for this job... They got the organ out of the their church and up on my trailer in no time flat. Now I noticed something but I didn't say anything at the time because well... Free is Free... They cut all the speaker wires right at the organ console and all they give me was one Rodgers M10 speaker to go with it... So after a long, careful, and exhausting drive back home. I had to put the 750 up in my garage until I can get my old hammond organ out of my house, because the 750 is going where the Hammond sits now, and my living room is not very big. So my question is... after taking off the rear cover and pulling very carefully both electronics racks open... I noticed there was a curious amount of trash, and bits of debris all in the bottom the organ... Then I seen the speaker wiring system... the wires looked pretty beat up... I don't know if that had been done in years past or the men did it while moving it out of their church to load it on my trailer, but I am pretty sure I will need to make new spade connectors and wiring for the speakers I will have to get for it... So all I need is help with what wires to go where... I can wire it up... I just need to know what wire goes where... I'm including some pictures I just took of the organ for you guys to check out too...

Thank you guys so much!! Any help is always very appreciated!!!

[jbird604]

Pretty decent organ. You ought to enjoy that a lot more than a Casio keyboard.

Looks like there was a resident rodent in the previous home! Just clean up the mess best you can and disinfect with Lysol spray or something if you like. Don't get anything wet other than the floor though.

The wires probably got pulled on pretty hard when the console was moved. The terminals are clearly marked so you know which speaker connects where. Each speaker cabinet will connect to one of the named terminals and to one common terminal.

You should have gotten two M10 speakers and another speaker that is obviously a "pedal" speaker -- big and heavy with one or two large speakers in it. If the originals cannot be retrieved, you may have to find some suitable replacements somewhere. For a home setup they don't have to be as heavy duty as in a church.

Observe "polarity" when wiring the speakers -- we use the "ribbed" side of a zip cord as the "+" conductor and the smooth side as the common. Be sure to connect it the same way at the terminal strip and on the speaker cabinet too.

-----------CORRECTION--------

There should've been four speakers total, going by the number of terminals on the strip. Swell, Great Flute, Great Main, and Pedal. The pedal speaker would be, as I said, a large and hefty one. The other three could all be M10's or some other type of non-pedal cabinet.

[Larrytow]

Congratulations on the new ( to you ) organ find, and successful moving job. There should have been more speaker cabinets that go with the organ ( they are actually Part Of The Instrument ! ) that were left behind at the church. You should contact the church and see about getting them. They really are not good for any other purpose than an organ sound system, so the church will not have a use for them. Many other speaker cabinets can be used with an organ like that, so it is not essential to have the ones that were left behind, just nice to have.

Some of the techs who are more familiar with Rodgers than I am will be along to tell you what goes where, and what options you have.

Finding all sorts of junk, dirt, and so forth inside organ consoles is very common. At least on yours it is not the type of dirt that is particularly concerning. If you were to have found mouse droppings, or even a dead one in it ( I have in the past ), that would be a cause to worry. As you expect, a good vacuuming is in order for your console. Just be careful not to poke the nozzle directly into any circuit boards that you might dislodge. With a decent shop vac, you can hold the nozzle an inch or two above the surface of things and get everything sucked up.

[johnbeetem]

There are some good discussions on Rodgers 750 speakers on the forum. By doing a Google search for "Rodgers 750B schematics" I found these:

https://www.organforum.com/forums/sh...iring-Speakers

https://www.organforum.com/forums/sh...-s-Rodgers-750

I have a Rodgers Trio 321C and it seems to use similar external speakers, i.e., an S-100 amplifier plus speakers for each channel. There are schematics for the speaker units towards the end of the Trio 321B/C service manual: https://www.organforum.com/gallery/d..._display_media

Here's my SWAG (scientific wild-assed guess): The terminal block has the four speaker channels described in the above two forum threads. The internal wires are fairly thin, so they're probably output signals for external S-100 amplifiers and not intended to drive speakers directly. The four channels are: swell main, great flute, great main, and pedal. Like my Trio, flute stops and "main" (everything other than flute) have separate amplifiers and speakers. There are two "common" terminals, which is probably "circuit ground". My Trio uses white wires for "circuit ground" and black wires for "chassis ground", connecting the two at the power supply.

It's hard to see what's connected to the Swell Main terminal and the Common terminal next to it. Is that a light grey wire labeled Swell Main? If so, there's probably a jumper wire between the two Common terminals since there seems to be only one white wire, which looks thicker. I would guess that to connect to the external speakers you'd need four two-wire cables, one for each amplified speaker unit. Each cable would connect to one of the four output terminals and one of the two Common terminals.

These are just a guesses and I've only been doing organ tech stuff since September. You should wait for other opinions before doing anything serious.

[ns9987]

Thank you guys so much for all the helpful advice!! I really appreciate it alot!! I'm going to call the church back where i got from and see if they still have it's additional speakers for it because I would like them to go with it, so I wouldn't have to buy new ones. I am also going to vacuum it out and see if i can get something wired up for the speakers! I will keep you guys posted with my progress!! Thank you guys so much again i really appreciate your help!!

[jbird604]

Best I recall, the 750 has amplifiers built in (which is unlike many other Rodgers analogs of similar vintage), so the wires go directly to ordinary passive speaker cabinets. There may also be some outputs (five-pin jacks) for optional external amps.

If it's impossible to locate the original speakers, you can use a fairly ordinary subwoofer, such as one I see at Newark.com (formerly MCM Electronics) that costs less than $100 with a 15" driver in a cheap but passable box.

The manual cabinets can be replaced by decent commercial sound cabinets, such as some MCM models with a 10" woofer and a tweeter. Not the highest quality speakers, of course, but they don't cost $500 either. Probably around $50 each.