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

switching.

 

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

back later.

 

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"

position. 

 

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).

 

 

Steve  WD8DAS

 

 Schematic of HW-16 modification