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Looking for Assistance with reviewing Schematic for my Transistor Radio to Amp Conversion.

Posted by Todd on March 7, 2013 at 3:30pm in Performances, How to Play, Lessons, Concerts

I have an old 1960's GE AM radio that I've had trouble converting over to a Cigar Box Amp.  Tried the usual ways.  Anyone here good with Electronic Schematics that can advise?

Here's the Schematic:  http://oi47.tinypic.com/14btdue.jpg

Here's the diagrams of the insides:  http://oi46.tinypic.com/108eahd.jpg

She worked okay when tapping into the volume knob... but played at a very low volume.  The radio itself is very loud so I must need to tap into the preamp or something???

Here's what she looks like:  

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Replies

  • Todd March 8, 2013 at 6:29am

    Thanks again Brian and Don!

    Moved discussion to:  http://www.cigarboxnation.com/xn/detail/2592684:Topic:1467634?xg_so...

  • BrianQ. March 7, 2013 at 8:28pm

    U should join dis Group:

    http://www.cigarboxnation.com/group/vintage-radios-converted-into-g...

    lots of conversion videos there

    • Todd > BrianQ. March 8, 2013 at 6:17am

      Thanks Brian!

  • BrianQ. March 7, 2013 at 8:24pm

    If u look @ the Cap(C3) there's a bold stripe going down the side w/ some -  - (Dashes) right? That's - neg other side is + pos just remember the opposite side of the stripe is + Positive.

  • Don Goguen March 7, 2013 at 6:36pm

    I would try tapping into the + side of C3  (desolder or cut the trace and don't forget the guitar cable ground) just after the volume control but I suspect there is just a level difference between the output of the pickup and the audio output from the tuner.  If so the solution is to add gain to the guitar.  A op amp chip on a small breadboard using the volume control from the radio would do.  Plenty of standard 8 pin chips and circuits on the web.  Do a quick google search for Op Amp guitar pre

    • Todd > Don Goguen March 7, 2013 at 7:52pm

      Thanks Don.  An Ipod worked fine, so that would make sense that none of my guitars were loud.. but I would have thought my acoustic with the LR Baggs preamp would jam... but it was barely louder than the piezo coming from the CBG.

      I'm sorry, but I'm a rookie at electronics mods... Can I just measure the voltage on each side of C3 by reading between C3 and ground to find the + side?

      • Don Goguen > Todd March 8, 2013 at 6:24am

        The Baggs pre is mainly a buffer amp and not intended as a gain stage.  The piezo is really high impedance and the pre helps with the relatively low input impedance of the amps.  Even if the output was doubled of what a mag pickup was, you are still in a low level situation.  The guys in the Mod section can likely help you out with resources and ideas.

        Here is a simple circuit I found using a common op amp chip.  Change the value of the two input resistors, you change the gain.

        Guitar Wiring Blog PreAmp

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