| I recently
acquired a Heathkit DX60B and wanted to operate AM mode as well as CW
with this equipment. I also wanted to mute the audio on the 75S3 and
SX100 I had available to use for receivers during transmission.
Inspired by the article about boatanchor antenna relay by Phil Salas,
AD5X, posted on his web site www.ad5x.com, and the desire to operate
without constantly turning the DX60 mode switch. I scoured
the Internet and old CQ and 73 magazines for ideas on adding PTT to the
I found several articles regarding methods of adding PTT to boatanchor
rigs and DX60. After reviewing them I had reservations about each
article. They worked on AM but not CW. Some used hard to find relays,
6.3 volt and 115 VAC, or had 6 or 12 volt AC going through the mike
cord. One used a 3PDT relay. So I set out to design a system using
readily available parts and would allow PTT on AM and CW operation.
First lets define the system requirements.
- Operate the
relay internal to the DX60 on DC.
- Use an
external Dow-Key antenna relay that was already available.
- Allow a PTT
mike, which the DX60 was not designed to use.
- Allow an
external amplifier to be switched on during transmit.
- Mute the
receiver audio on transmit.
- Switch the
125 volts AC to the accessory socket with the PTT to operate the
- Key the
grid block keying on an external vfo and the DX60 on AM and CW.
- Key the
DX60 grid block circuit on AM and allow a key to operate on CW.
- Allow for
an internal antenna change over relay if an external relay is not
- Allow for
switching 125 volts AC to the VFO with the DX60 on-off switch.
A trip to the local parts emporium, Radio Shack, found a 3-circuit
¼ inch phone jack and plug for the microphone. Also I found
a small epoxy DPDT relay that operated on 12 vdc and would key with a
minimum of 9 volts, RS PN: 275-249. It is rated at 5 amps at 240 volts
AC, great for switching the 125 VAC circuit. I also picked up
a couple chassis mount phono plugs for the external switched circuits
and a small SPDT toggle switch for the CW/AM keying control.
Now let me advise that the HG-10 VFO that I own has been modified to
add it’s own power supply rather than use the DX60B power via
the accessory socket. This required switching the AC to the VFO with
the DX60 switch. I also wanted to have a separate output coax from the
VFO to the DX60 and a separate coax for keying the VFO grid block
circuit. This required adding a phono socket on the rear lip of the VFO
and a wire to the keying circuit inside the HG-10.
Now to the actual changes in the DX60B. First I removed the mike
connector from the front panel. I installed a 3-circuit ¼
inch phone jack in the same hole the mike connector had occupied. I
connected the mike input to the ring contact so the tip could be used
for the PTT. This is standard for most PTT mikes. The old mike
connector could be added to the rear deck of the DX 60B, but I did not
Next the AC neon bulb and its mount was removed from above the mike
connector. I installed the SPDT toggle switch in this hole, loosely, as
it will be removed later to when it is wired. The VFO dial
lights will show that the AC is on and later I plan to add illumination
to the DX60 meter.
I chose to mount the internal relay on the backside of the metal shield
in front of the oscillator circuit. There is plenty of room there just
above the capacitor, looking at the DX 60 from the bottom, feeding from
the oscillator to the driver. After wiring and checkout, I used hot
glue gun to secure the relay to the metal shield making sure the
contacts had plenty of clearance to the bottom cover.
Now to the wiring changes in the DX60B. First I changed the 100 ohm 7
watt HV filter resistor to a 10 watt unit. I also changed the 240 ohm 2 watt LV filter resistor to two 470 ohm 2
watt resistors in parallel. A 240 ohm 5 watt resistor could have been
used but I had the 2 watt resistors available. They are notorious for
failure in the DX60B. These resistors had been burned and opened up when I got the DX60B, so
they needed replacement.
- Next I
removed the 2 white wires from the accessory socket pin 8 and moved
them to pin 3 (NS). Carefully pull them down and back and they will
- Now tape
the relay in its mounting place on the metal shield and measure a wire
to run from pin 3 to the relay on one of the normally closed contacts.
I chose the one closest to the shield. Install this wire to pin 3 (S)
and the relay (S). (S) and (NS) stand for solder and no-solder.
- Now measure
and install a wire from the relay NO contact (S) to the ground lug of
the VFO input phono jack (S).
- Now measure
a wire to go from the relay Common terminal to accessory pin 8. Install
this wire (NS)
- Measure a
wire to run from acc pin 8 (NS) to the switch mounted above the mike
jack. It will go on the terminal furthest away from the mike jack (S).
Remove the switch for wiring. (NOTE: This step is only needed if you
want an external grid block key line for a vfo). Install a phono jack
in the space about 1 inch from the accessory socket mounting screw and
toward the nameplate. Add a wire from the center terminal of the jack
(S) to pin 8 (S).
- Now measure
2 wires to run from the switch above the mike jack to the key jack. I
cut them a bit long, about 3 to 4 inches, and then twisted them into a
twisted pair. I ran mine across the front of the chassis as close to
the bottom underside as possible. I recommend using 2 colors to make
the next step easier.
- Solder one
end on each wire to the switch, one on the center and one on the free
outside terminal. Now you can remount the switch. Put the terminal with
the wire from acc pin 8 away from the mike jack. The other
end of the twisted pair will next be connected.
- Remove the
wire from the key jack. This will be connected to the wire from the
switch center contact, common, be soldered and covered with sleeving.
Be sure to put the sleeving on the wire before connecting and soldering
the wires together. Don’t ask!
- Solder the
free end of the other wire from the twisted pair to the key jack.
- Remove the
wire from accessory pin 5 and add another wire extension to reach to
the relay NO contact. Be sure to place a length of sleeving over the
wire to insulate it after soldering the extension to the wire from acc
- Measure and
cut a wire to run from acc pin 5 to the relay common contact. Strip
ends and solder to pin 5 and the relay.
- Remove the
power transformer wires (2) and AC input wire from the end terminal on
the strip by acc pin 8 and move to the opposite end of the strip.
- Add a
1N4001 to 1N4007 diode from acc pin 2 (anode) to the end terminal of
the strip by acc pin 8. Add the 1000 mfd 16 volt cap negative terminal
to the ground terminal of the strip holding the HV rectifier diodes.
Add a wire from the capacitor plus terminal (S) to the cathode (band)
of the diode from acc pin 2. Measure and install a wire from the diode
cathode in previous step (S) to the relay coil terminal (S).
- Measure and
install a wire from the mike jack PTT terminal (S) to the free relay
coil terminal (S).
- Check all
the solder joints on the relay, acc socket, mike and key jack to assure
proper connection, and no shorts. Place a piece of black tape
over the relay contact pins and connect a dummy load to the
DX60B. Turn on the DX60B. After warm up, key the mike and
assure the small relay in keying. Turn off the DX60B.
- Plug the
wires from the external 115 volt relay into acc socket pins 5 and 6.
Set the mode switch to AM and key the PTT. The external relay should
operate. Set the mode switch to Standby.
This completes the basic modification of the DX60B for PTT.
The external relay should have its cabling made up now as needed for
the equipment in your station. Suggested cabling is covered in the
operation section #2. Length of cables will be custom for your setup.
As mentioned, I had a separate power supply in the HG-10 VFO and needed
a way to turn it on and off with the DX60B. I drilled a 3/8 hole at the
end of the back panel near the power transformer and installed a rubber
grommet. I cut the 3 outlet end off an extension cord leaving about 10
inches of wire. I passed the 2 conductor zip cord through the grommet
and soldered the ends to the two AC input wires at the end of the
terminal strip by the grommet. The large outlet conductor wire to the
end terminal, AC neutral, white wire of house socket. The small outlet conductor to the power transformer and circuit breaker
connection on the second terminal. This allows the DX60 B main power
switch to turn on the DX60 B and the VFO.
Operation is as follows.
- Keying the
mike causes the small relay to close, switching 125 volts to the
accessory socket to operate an external relay and switching the vfo
grid block line from the negative bias to ground thus turning on the
vfo. If the small switch above the mike is set so the handle is toward
the mike jack the DX60 will transmit a carrier. If the switch
handle is pointed away from the mike jack the key jack will be
operating. and an external key in the jack will allow CW
operation. For CW semi-break in—use the PTT switch on the
mike to turn on the transmitter. If a foot switch is desired for
semi-break in the wire from the mike jack to the relay can be routed to
acc socket pin 7 or another phono jack can be added to the rear panel
and connected to this wire. Adding a foot switch going to acc socket
pin 7 or the phono jack will allow semi-break in on CW.
external ant relay should have a set of SPDT or DPDT contacts on its
side. These are wired so on one section the common terminal is ground
and the NC terminal has a wire to the receiver mute terminal. I used a
length of Zip cord in my station for this function with one wire on
ground at the relay and at the receiver. The second wire goes from the
NC terminal to the receiver mute terminal.
- The NO
terminal has a shielded wire with center to NO and shield to ground
(Common) and a phono plug or other connector needed to key the external
amplifier. If you wish to monitor your CW signal, then a variable
resistor, potentiometer, of 10 to 50 K ohms is connected from the mute
terminal to ground. This will allow you to set the volume of the
monitor signal on CW.
The schematic for these modifications is
shown below. I can be contacted at w4bws at arrl dot net.
Click on schematic for larger version.