Subj: [HeathKit] HW-16 anti-chirp mod
Date: Sun, Jul 2, 2000 8:26 PM EDT
Updated: December 2012
The Heath HW-16 transceiver's transmitter has a tendency to be chirpy,
even when running crystals rather than a VFO. I've spent a lot
of hours trying to make my old HW-16 oscillator unconditionally stable, and
I've about given up. It is just too hard to grid-block key an oscillator and
get a solid note from a wide variety of crystals.
As an alternative I've come up with a "no-new-holes" modification to allow
the operator to select normal break-in keying OR manual transmit/receive
With an active crystal or good drive from a VFO, you can leave the switch in
the "break-in" position and the transmit/receive switching is automatic as
you send. If you find yourself with a crystal that is slow to start, and
chirpy, switch to the "transmit" position. In this position the receiver is
muted (same as with the key down in break-in) and the oscillator is turned on
throughout the transmission. The rest of the transmitter stages are
grid-block keyed as usual. The result is the best sounding signal ever to
radiate from an HW-16.
I've noticed that many people hate the receiver overload clicks and screeches
associated with the break-in on this rig anway (they can be reduced by adding
a 0.47uF cap from the base of Q1 to ground, by the way), so the loss of
break-in is not a big deal.
To kill these noises most HW-16 operators tend to reach over and
turn the receiver audio down while transmitting, defeating the purpose
of break-in anyway. Why not reach over and throw a switch to choose transmit
or receive mode?
The modification is simple. Remove the upper crystal socket and use the two
holes for a mini DPDT switch and an LED in chrome holder (both from Radio
Shack). No drilling needed and it would be simple to put the crystal socket
One side of the DPDT switch is used to interrupt the connection of the 47k
oscillator grid-blocking resistor R1 to the terminal strip where it gets the
negative voltage (keying line). In other words, one switch wire goes to the
end of R1 away from the osc tube, and the other wire goes to the terminal
strip where R1 was previously connected.
Then move the wire that originally connected "point Y" on the receiver board
(the RX muting line) to the rear-panel octal socket pin 8 over to now connect
point Y to the same end of R1 where you connected the switch.
Switch open is the "transmit" position, switch closed is the "break-in"
See the attached schematic - the text description can be confusing.
The other half of the DPDT switch is used to turn on the LED so you get a red
light when in manual transmit mode. Grab the 6.3 vac from the nearby meter
pilot light, run it thru a 1N914 diode and 1k resistor to turn it into
current-limited DC for the LED (or I guess you could use a small 6.3 v lamp
in a miniature holder).