A gutted old speaker was used for the enclosure. There wasn't much room left in it after putting in a speaker, transformers for the filaments, high voltage and low voltage power supplies and circuit boards for the audio amplifer, band pass filters, inverting amplifiers, high voltage delay and high and low voltage power supplies. The audio is mixed through two resistors to convert it to mono then fed into an LM386 which drives the speaker and also acts as a preamplifier for the four analog bandpass filters. Each bandpass filter controls a magic eye tube. The analog bandpass filters are from a design I found online and are op amp based. Center frequences for each of the channels are 300Hz, 600Hz, 1.2KHz and 2.5KHz. Each output from the bandpass filters are fed to inverting amplifers which convert the 0 to +2 volts signal to a 0 to -4 volt control voltage to drive the tube grids. There is also a 12F683 microcontroller which controls a solid state relay wired into the primary of the high voltage transformer allowing the tubes to fully warm up before appyling any high voltage. The tubes used are 6E1P's purchased on ebay.