| Technical Information in PDF | 
  | Installation andOperating
 Instructions
 |  | Installation and Operating | 
  |  | Installation and Operating | 
  |  | Installation and Operating | 
  |  | Installation and Operating | 
  |  | Panel Template | 
  |  | Installation | 
  |  | Operating | 
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  | Radio Specific  Installation  Instructions  Figure 4 installation drawing modification for specified radios. |  |  |  |  | 
  |  |  SPA-400 For ICOM A3, A6 , A22, A24 Radios |  SPA-400 For King KA 134 Audio Panel |  SPA-400 For King KMA 20 Audio Panel | 
  |  |  |  |  SPA-400 For U-174 / U Headset Jacks | 
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  | Modification |  | It allows pilot and co-pilot to transmit and receive on the aircraft radio and intercom between themselves, while back passengers can have a separate conversation without interrupting the front two. | 
  |  | Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1528, (SPA-400 S/N 6069006 to Current & SPA-600 S/N 1102528 to Current) | 
  |  | Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1440, (SPA-400 S/N 6053486 to 6069005 & SPA-600 S/N 1101839 to 1102527) | 
  |  | Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092-4, SPA-400 Panel Mount, S/N 61960 to 6053485 | 
  |  | Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092-3, SPA-400 Panel Mount, S/N 60975 to 61959 | 
  |  | Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092-2, SPA-400 Panel Mount, S/N 60500 to 60974 | 
  |  | Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092, SPA-400 Panel Mount, S/N 60001 to 60499. | 
  |  | This modification is used when a Sigtronics SPA Intercom is connected to a radio or audio panel that has a low impedance headphone output (less than 100 ohms). | 
  |  | Installation Instructions for use on Sigtronics Panel Mount Intercom Systems | 
  |  | This modification applies to a Sigtronics SPA-400/600 or ST-400 / ST-600 installations. | 
  |  | Add pilot isolate to a SPA-400 / SPA-600 Intercom. | 
  |  | Music input options for Sigtronics SPA panel mount intercoms. | 
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  | Trouble-shooting |  | Instructions designed to assist avionics technicians in diagnosing comm? radio transmit problems following intercom installation. | 
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  | Helpful Hints |  | Communicating in Unusually High Noise Environments |