Conn Organ Amplifier Chassis

[junkin8ez]

I got this off of Ebay with hopes of converting it to a guitar amp.
Does anyone have a schematic or know the model #? Or am I wasting time?
vintage 1958 conn 2 channel amplifier.

1 channel is push pull 6L6 the other is push pull paralell 12v6

uses 2- 6L6, 4- 12v6, 3- 12ax7, 2- 12au7 & 5u4 & 5y3 rectifiers.

weighs 25lbs and is 21" long.

has rca inputs & level adjustments for each channel. Has input for tremolo.
Any help would be great.

[6267]

It has three output sections, one 2x6l6 cathode biased, one 2x12v6 cathode biased, and something very strange. Two of the 12v6s are connected anode-to-anode with a huge plastic cap, and then the anode leads run off chassis. There must have been some other board which used this signal (I think?). It may have been a variable frequency inverter to drive a leslie motor??! The 6l6 and 12v6 transformer stages each get 2x12ax7 for a preamp, and the 12v6 weirdo stage got one as a preamp. The 6l6 stage sounded fine as is, but I converted the 12v6 to 6v6 (since I had some) and it sounded like it lacked bass. This chassis is my summer project, although I'm finishing a different amplifier first. I ripped out the wiring for the weird 12v6 stage as well as the large cap, I'm going to build an octal preamp for the cathode biased 6v6 outputs and use all 5 noval sockets to do a more complex amp for the 6l6s. I think it'd be neat to have the output of the octal-6v6 herzhogable into the 6l6 amp! It might be wiser to have the 6v6s drive a frequency specific set of speakers in a custom cabinet, and let the 6l6s handle bass.

[6267]

From my research (a while ago, no link) this chassis powered around 72 additional tubes throughout the organ (thus that damn heavy power transformer). It only has a 12.6v heater winding, so you have to get creative to use 6.3v only tubes. I imagine it has both heater current and B+ current to spare, so I guess with that PT those issues will not be as limiting. The OPTs look a little small to me, but I haven't been experimenting to extensively. There's a little plug in between the 12ax7s with 4-5 prongs, it'd go to a tone control or volume control in the original circuit. There's another octal plug with 2 fat wires and I think three smaller wires. The smaller ones are speaker leads from the transformers, they share a grounded side internally. The fat wires came off that ridiculous 12v6 transformerless thing. Another octal on there is the power switch and pilot, it has 4 wires, two must be connected to "turn on". You should verify which plug is which by examining the circuit. I believe this chassis could make for a mighty fine amplifier.

[junkin8ez]

Thanks For Your Help! I may be getting in a little over my head with this.
Do you have any drawings of what you did? Should I ditch the monster transformer? There is a tremolo input.Is that one of the channels you have?

[6267]

I haven't done too much with mine yet, I'm still trying to finish another amp and playing the cap and test game. The big transformer is the power transformer, and it may not have anything like a modern equivalent. Keep it, you will have current to spare! The little, open framed transformer on the top is more likely worth replacing, you could use a fender replacement OPT (check tubesandmore.com and webervst.com)...could even have a stereo 6l6 amp that way. As it's wired, there are two tubes before the 6l6s, and two tubes before the 6v6s (RCA jack---->voltage amp---->plug---->phase inverter--->6l6s/6v6s).

How to make it turn on (from memory so use wise judgement ):
1.One of the octal plugs (i think the metal shielded one) has two wires which can have a switch (and fuse!) placed between them. The wires will be connected to the black wires of the big transformer internally (seen from the underside). Do not switch on yet.

2. The other octal plug (mine has no shield) has the speaker hookups. Looking on the underside, a green or yellow wire (can't remember, could be different on your model) will clearly run from each smaller transformer to the socket. Each of these wires is the + speaker lead. The - speaker lead will be black and is attached to the silver ground bus. You can probably figure out the speaker connections by examining the underside, each transformer will send a wire to this plug (the 6l6 transformer seemed to send two in my amp, perhaps a 16ohm lead. It was not wired to a used pin on the socket though, but an unused one.

3. Connect the speaker leads to 2 8ohm speakers (we'll ignore the weird tremolo thingy for now, actually pull the 12v6s that are farthest from the 6l6s, this won't hurt anything). Making sure the speakers are *well* attached, flip the switch installed in step one (or unplugged, twist the two wires together and plug in). It *should* light up, no smoke, and you should be able to hook up RCA sources (I used an iPod for the test) and hear them from their respective speakers. There isn't much preamp, so it will be kinda quiet. If something seems amiss, pull the plug.

Hopefully that's helpful, that's about as far as I've gotten with the damn thing so far, in three not so easy steps. It seems like yours came with the tubes, so you're a step ahead of me! If you want I'll go over and check the wire colors if you need them, esp. for the speakers (i hope I explained that ok). I do know that the octal jack near the accessory socket is designed for running a certain type of stereo leslie speaker, so it may be possible to retain that functionality. The organ used nearly 100 12au7s to generate all of its tones, and the big transformer powered them all plus the power amp I believe. The power supply I believe is a voltage doubler, so the transformer really can source some current!

[junkin8ez]

Thank you so much!!!! I do have a layout sticker on the side.There is a 5 prong wire"Expression Controls" that appear to go to a "main level" pot & a "Tremolo Level" Pot. It almost looks like the Expression control was from a switch on the organ to switch the channels from normal to tremolo. I could be wrong(just hoping it would be that simple).Thanks again!

[6267]

I haven't figured out the tremolo yet, but that expression control plug is the one that you'd put a tone control or volume control on, that plug has a central ground, and the two wires on each side are the signal path for the 12v6 and 6l6 channel, I just connected them to test. There's already a cap inside, so they're decoupled. The ebay seller pointed out to me that the caps in the amp already are the same supplier that made caps for the early fenders! It is possible that some part of the tone control on the expression plug sent a copy of the signal to the tremolo, although I read somewhere that Conn organs sent certain voices to the clean amp and other voices (generated seperately, flute i think) to the tremolo amp.

[x44d80]

I have this amp!

I have this same chassis and built guitar amp out of it. I used everything from the Conn organ I got at a thrift shop including the weaved cane speaker covering. It looks pretty cool but it's fairly weak on volume and can't be driven to distortion. I'd really like to mod it into a blues type amp but this will be my 1st try. I understand circuits and can read a schematic but don't quite understand the theory of tube amp circuits. If someone could point me to a thread or site so I can read up on tube amp circuits I'd appreciate it. Thanks, Brent

[Frankenamp]

I just found one on fleabay that is in pretty decent shape (one of those where the price was right and I had to get it...) Anyhoo, I'm very impressed with the construction of the amp, the origional owner said that it was built in 1958. It uses a interesting 'buss line' grounding system... The amp is marked AN 266 and it is about 6" by 21" long. I was considering making a guitar amp, but it's such a nice piece... (like the other organ amp I found- 1-6SN7 driving 4- 6L6's cathode biased with monster iron and 3- 4mfd bolt on caps... I just can't bring myself to injure such a work of beauty...) decisions, decisions... I'm wondering if I can make it a 2 channel amp by swapping the 4 12V6's with a pair of 6L6's ... (new OPT) Anybody know if the tremolo circuit is onboard or if it's farmed out to a subsection?

Thanks in advance

[6267]

The tremolo on mine seems to have gone out from the power oscillator (2x 12v6) to one of the octal plugs. Seems offboard and weird! It is a two channel amp, at least if you have the 6L6 & 12v6 model. You have to monkey with the heaters a bit since the 6L6 cathodes are used as balance resistors & the cathode resistor is used to bias them +. The 12v6 can be replaced by making the two used sockets wire their heaters in series (6.3v + 6.3v = 12.6v, naturally), but this requires a bit of rewiring in the amp. The output transformers are both a bit small for big power, but would work fine with relaxed 6L6GA or GB cathode biased circuits...I paralleled another 6v6 OPT with the onboard one and ran it up to 45w. There is a socket near the preamps that needs to be bridged to get any gain into the power amp...I thought the amp was really quiet until I found that. I ended up redesigning the preamp because it was not setup for my needs, there's plenty of possible options, and extra sockets for all the bells and whistles + stereo.

Personally, I'd get a $50-75 100w output transformer, switch it to solid state recto and parallel 6 6L6GCs as one channel for a guitar amp. Fun chassis to work with, lots of options, but it weighs A LOT! The power iron is irreplaceable on my budget, so I recommend being very careful!

Currently mine was used as a vocals amp & mid/hi driver in a sound rig we used for a bit. It also doubles as my stereo & PA...I have an outboard preamp that I connect into it. It was somewhat underpowered for the room, but sounded great. I am using solid state rectification, and it's at about 50w a channel now with TV tubes & 6CA7s.