Amplifier Schematics - Old Frets Many Valco amp don't follow existing schematics and can be considered transitional circuits between different eras, so consider these to be loose guides rather than gospel truth. Because many models are identical between brand names, a Supro link may bring up a Gretsch schematic, for example. National Amp Circuit Diagrams or Schematics National de luxe amplifier Model B Dated 1938. This circuit diagram is pasted inside the amp case, and is only a few inches square. I can not 'blow' it up any more from the picture I have, and I can't 'scan' it.