7-inch (18-cm) reel and, consequently, the result- ant playing time. Playback To playback a recording, thread the tape and locate  the  desired  starting  point  by  using  the high-speed lever. Set speed selector for the speed at which the tape was recorded. Push down the play  key;  then  adjust  volume  and  tone  controls to suit. NOTE:  While  modern  recorders  are  almost foolproof,   many   a   good   recording   has   been destroyed   by   accidently   playing   it   on   the RECORD  position.  Always  use  the  correct  con- trol. MONAURAL.—If   the   tape   is   a   dual-track recording, turn over the takeup reel at the end of the first track and put it on the supply spindle. Rethread  the  tape  and  play  it  in  the  opposite direction. When  you  are  playing  back  a  recording,  you must be familiar with the recorder that you are using.  Follow  the  instructions  published  in  the operation   manual   for   the   specific   recorder. Some  recorders  are  capable  of  playing  back 4-track  recordings.  The  model  shown  is  such  a recorder.   When   playing   a   2-track   monaural recording  on  this  specific  model,  set  the  head track  selector  on  2-TRACK.  This  positions  the heads  as  shown  in  figure  7-21.  When  playing back  4-track  monaural  recordings,  set  the  head track  selector  on  “A”  or  “B”  and  run  the  tape in that direction which gives the desired track to be  played.  Figure  7-21  illustrates  the  “A”  posi- tion  of  the  heads.  You  will  notice  that  in  the “A”  position,  you  can  play  back  monaural tracks 1 or 2. Figure 7-21 also illustrates the “B” position  of  the  heads.  Notice  that  the  “B”  posi- tion permits you to play back monaural tracks 3 or  4,  depending  on  tape  direction. STEREO.—When  you  play  music  before  or during  a  presentation,  you  may  want  to  play stereo  recordings.  To  play  a  stereo  recording, connect  the  stereo  preamp  jack  to  an  external amplifier  and  speaker  system,  placing  the speaker at least 7 feet (2.3 m) to the right of the tape recorder. If you use a stereo amplifier, con- nect  the  regular  preamp  output  jack  to  the  left channel input and the stereo preamp jack to the right channel input. In this arrangement the out- put  stage  and  the  speaker  of  the  tape  recorder are not used. Thread the tape and locate the desired start- ing  point.  Remember  that  moving  the  high- speed  lever  to  the  right  causes  the  tape  to advance  at  a  much  higher  speed  than  normal. Set the speed selector at the speed for which the tape  was  recorded.  If  you  are  playing  back  a 2-track stereo tape, set the head track selector on 2-track.  Figure  7-21D  illustrates  the  2-TRACK position  of  heads  for  stereo  2-track  playback.  If you  are  playing  back  a  4-track  stereo  tape,  set the selector on “A,” Figure 7-21 E illustrates the “A”   position   of   heads   for   stereo   4-track playback.   After   positioning   the   selector,   push down the PLAY key and then adjust the volume and  tone  controls  for  proper  balance. When  playing  2-track  stereo  tapes,  you  will have to rewind the tape at the end of the reel to prepare for the next playing. Figure 7-21D shows that  the  signals  are  put  on  the  2  tracks  in  the same direction. The 4-track stereo tapes contain additional program material; therefore, you may turn  the  full  takeup  reel  over  at  the  end  of  the first  side  and  place  it  on  the  supply  spindle. Figure   7-21   E   illustrates   that   the   program material  is  put  on  tracks  1  and  3  in  opposite directions from tracks 2 and 4. After turning the reel,  leave  the  head  track  selector  knob  set  on “A”  (figure  7-21  E).  At  the  end  of  the  second side this tape will be ready for the next playing without  rewinding. PLAYBACK   THROUGH   EXTENSION SPEAKERS.—Figure  7-22  illustrates  connec- tions to be made to play back through extension speakers.  Plug  the  attachment  cord  phone  plug firmly  into  the  extension  speaker  output  jack. This   automatically   silences   the   recorder’s built-in speaker. Attach the alligator clips to the terminals   of   the   extension   speaker.   It   was pointed  out  previously  that  preferably  the speaker   should   be   of   8-ohm   impedance, however,  speakers  of  impedances  ranging  from 3.2  to  16  ohms  may  be  used.  Use  the  recorder volume  and  tone  controls  to  control  the  exten- sion speaker. 7-42