‰  NOW 40 WPM  ‰  TEXT IS FROM NOVEMBER 2012 QST  PAGE 55‰
THE TRANSMIT LED SHOULD GO OFF AFTER A DELAY OF APPROXIMATELY 1R5 SECONDS.
TRY THIS TEST AT BOTH EXTREMES OF THE DELAY POTENTIOMETER RANGE.  AT ONE
END THE LED SHOULD GO OUT ALMOST IMMEDIATELY ABOUT 0R25 S WHEN THE TUNE
SWITCH IS RELEASED TO A MAXIMUM OF APPROXIMATELY 3 S AT THE OPPOSITE END OF
THE CONTROL TRAVEL.  SET THE DELAY CONTROL TO MAXIMUM FOR THE MOMENT.  PLUG
YOUR KEY OR KEYER INTO J4 KEY/KEYER AND SEND SOME CW WHILE MONITORING THE
SIDETONE WITH YOUR HEADPHONES.  THE SIDE

THE TRANSMITTER, AND ROUTING THE SIDETONE TO THE HEADPHONES.  RELEASE THE
TUNE SWITCH AND THE TRANSMITTER AND SIDETONE WILL GO OFF IMMEDIATELY AND
THE SYSTEM WILL CYCLE BACK TO RECEIVE AT THE END OF THE PERIOD SELECTED BY
THE SETTING OF THE DELAY CONTROL.  THE CONTROLLER CAN BE POWERED FROM A
STANDARD 12 V WALL WART POWER MODULE OR FROM THE STATION 12 V POWER SUPPLY.
CONSTRUCTION THE CIRCUIT IS SIMPLE ENOUGH THAT IT COULD EASILY BE
CONSTRUCTED ON A PIECE OF PERFORATED PROJECT BOARD.  I HAVE GOTTEN LAZY IN
MY OLD AGE AND TO SAVE TIME HAVE CIRCUIT BOARDS MADE FOR MOST PROJECTS.
THE PRINTED CIRCUIT BOARD LAYOUT DETAILS CAN ALSO SERVE AS A GUIDE FOR
PERFORATED BOARD CONSTRUCTION.  I PACKAGED MINE IN A NICE BUT RELATIVELY
INEXPENSIVE HAMMOND ENCLOSURE SEE FIGURE 2 THAT IS INCLUDED IN THE PARTS
LIST.  THE 2N4401 NPN AND 2N4402 PNP TRANSISTORS SPECIFIED ARE WIDELY
AVAILABLE.  OTHER GENERAL PURPOSE NPN AND PNP UNITS COULD EASILY BE
SUBSTITUTED.  JUST VERIFY THE LEAD ARRANGEMENT AS IT MAY NOT FOLLOW THE
CONVENTION OF THE TRANSISTORS I USED.  THE RELAYS SPECIFIED IN THE PARTS
LIST K1 AND K2 HAVE INTERNAL PROTECTION DIODES ACROSS THE RELAY COILS AS

KEYBOARD OR COMPUTER INTERFACE NO BLOWN SWITCHING TRANSISTORS.  THE
POLARITY OF THE VOLTAGE BEING SWITCHED DOES NOT MATTER, SO MODERN GEAR 
POSITIVE LOW VOLTAGE KEYING CIRCUITS, VINTAGE CATHODE KEYED POSITIVE HIGH
VOLTAGE, OR VINTAGE GRID BLOCK KEYING NEGATIVE HIGH VOLTAGE RIGS CAN ALL BE
KEYED.  K3B DOES HAVE MAXIMUM VOLTAGE 350 V AND CURRENT 120 MA LIMITS.  TO
ALLOW FOR A REASONABLE SAFETY MARGIN, IF YOU PLAN TO KEY A CIRCUIT OF MORE
THAN 300 V AND/OR 100 MA, YOU SHOULD USE THE KEYED XMIT LINE TO CONTROL AN
EXTERNAL RELAY THAT CAN HANDLE THE VOLTAGE AND CURRENT DEMANDS OF YOUR RIGS
KEYING CIRCUIT.  THE REMAINING CIRCUITRY IS ASSOCIATED WITH THE SIDETONE
FUNCTION.  Q6 AND Q7 FORM AN AUDIO OSCILLATOR WITH A FREQUENCY OF
APPROXIMATELY 650 HZ.  THE OSCILLATOR RUNS CONSTANTLY AND, WHEN THE UNIT IS
KEYED, THE SOLID STATE SWITCH OF K3A ROUTES THE SIDETONE TO THE CONTACTS OF
K2 AND FROM THERE TO THE HEADPHONES.  ESSENTIALLY THE UNIT AUTOMATICALLY
MONITORS YOUR KEYING WITH THE SIDE TONE, BUT WHEN THE SYSTEM SWITCHES BACK
TO THE RECEIVE MODE, YOU WILL HEAR THE OUTPUT OF THE RECEIVER.  VINTAGE
VACUUM TUBE TRANSMITTERS NEED TO BE TUNED A SIMPLE MATTER WITH A STRAIGHT
KEY BUT MORE OF AN ISSUE WITH A KEYER.  THE TUNE S2 SWITCH IS A NORMALLY
OPEN, MOMENTARY CONTACT PUSHBUTTON SWITCH.  PRESSED AND HELD, THE SWITCH
FUNCTIONS JUST LIKE THE KEY, TRIGGERING THE SYSTEM INTO TRANSMIT, KEYING
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ