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Conn Organ Chassis & Tube ID

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  • Conn Organ Chassis & Tube ID

    Hello all,

    Somehow I got interested in these home-built tube amps and started lurking here; so naturally you guys get to deal with my moronic questions. Just a short intro: My name is John, I am a graduate student in Materials Engineering working with carbon nanotube/polymer composites. I thoroughly enjoy all types of music. I play (attempt) blues, surf, and 90's rock. Looking to buy an old Music Man 210 HD130 (only after reading Forrest White's book)...

    I went and picked up a free Conn organ (found on craig's list) and hope to eventually hack together some sort of a guitar amplifier. Before I start working on the schematics I would like to know "what i've got", maybe some of you could give insight into the potential of this chassis and drop any personal experience working with this particular setup. I also need help identifying the big RCA tube pictured. The label for this tube on the chassis appears to have been victim of the hole saw/punch used to make the socket hole! All the other tubes are well labeled. The back of organ had a large rack of transformers/12au7s, 1 for each note?, and I assume that the "heater" socket and "power sockets" feed those?

    Thanks in advance and sorry for the poor picture quality.

    John T.
    Attached Files

  • #2
    Hey there John. Glad to see your new recycling project .

    Do you have access to some RCA receiving tube manuals? You can find PDF's of them online. I have the RC-14 and RC-30, between those two I can usually look up any tube (RC-14 has some older, obsolute tubes). You can also google for tube numbers and find data sheets (usually).

    The large tube pictured is hard to ID from the picture. An organ amp I converted had a similar tube and it was a "regulator" tube.

    A peek inside the chassis would be helpful. I only see one transformer pictured. To make a guitar amp you're going to need a power transformer and an output transformer, at minimum. A power transformer will likely have many wires connected to a lot of things (AC inputs, heater outputs, high voltage outputs, center taps, etc) wherease your output transform will probably just be a center tap, 2 inputs, 2 outputs (to a speaker), and a bunch of unconnected taps.

    Because I didn't see anything that is obviously a power tube I'm guessing the transformer pictured is a power tranny.

    I would say your first order of business is to find out what kind of B+ voltage you can derive from that power transformer. Then you apply some tricks to get the B+ you really want for whatever circuit you're building, then find a place for an output transformer.
    Check out my signal generator for your iPhone or iPod Touch.


    • #3
      Thanks for the replying and sorry for posting in the wrong spot originally.

      I found 2 output transformers (maybe audio?) on the back of the organ that I removed and have hooked up to a small 10VAC source to check the winding ratios. I also removed the power transformer (the big one pictured) and am attempting to do what you said, identify the voltages available. According to the NEETs manuals, the higher voltages will have smaller wires and the lower voltages will have larger wires? This is confirmed when hooking up to the 10VAC source I built. When I plug in 120VAC from the wall, i hear a popping/hissing. I took the caps off and it appears that the wax is melting. Is this normal? Or is it moisture boiling off? I read that the older sources were used to 110 and not the higher wall voltages in use today. Is that the problem?

      There are tons of components on the organ, so hopefully I can find enough parts to assemble something like the Fender Champ circuit. Am I correct that the octal sockets (I have 2 on this chassis) will run a 6L6 or any other octal tube (of course using the correct wiring)?

      Thanks again.


      • #4
        I don't know about the wire gauge. I don't remember seeing differing gauges in my organ's PT. One thing I remember is there was 4 of the same color (or 2 same color, 2 that color + a stripe) that went to the rectifier. Once you figure out which side is primary and which is seconary you can guess at the rest. It will take some reasoning but as long as you understand what a PT has you'll figure out what wires are what. Herer's a table of the wires that I found on my PT: Fender Bassman 5B6 amplifier - Projects - Audio Artillery

        Regarding the hissing you're hearing... dunno. Transformers can hum. I'd be very cautious, personally electronics that make noise spook me.

        Octal sockets - yes, an octal is an octal. Will be fine for 6L6/6V6, rectifiers, etc.
        Check out my signal generator for your iPhone or iPod Touch.


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