Heathkit HW-8 Mods Information



Heathkit HW-8 Transmitter Mods by KO6KA
Complements of the KB7RGG Nostalgic Kits Central Website
Reprinted here with permission from the author

These are the mods to my HW-8, as of July 1995, with reference to "The HW-8 Handbook" by Mike Bryce, First Edition, Second printing. DISCLAIMER: I've only worked on one HW-8; your unit may vary.

Mods 1,2,3, and 5 refer the schematic diagram on page 32. I used a "Solder Wick" braid to help desolder and remove components.

1.  Hard keying

My mod is identical to "Keying waveform" by G4HWZ on page 13. It's a 0.47 uF mylar capacitor from base to collector of Q11. Bend the leads into a gull-wing shape, add solder and flux to the traces underneath Q11, then while gently pressing the capacitor toward the bottom of the board, tack solder the leads onto the traces.

2.  Heavy keying

My mod is similar to "Choppy CW fix for the HW-8" by W3HVK on page 27. Instead of wiring transistor Q12 as a diode, I removed Q12 and substituted a silicon junction diode rated at least 100 mA. I used a 1N4004. The striped cathode end goes in the emitter hole and anode lead goes in the collector hole. Remove R67 between the Q12 base and ground, but leave R66 in place.

3.  Key line current dumping

My mod is similar to "Break-in delay modification" by KR0U on page 30. I put 100 ohm 1/2 watt resistors in series with both leads of C92.

4.  Motorboating

My mod is similar to "Anti-motorboating for the HW-8" by KR0U on page 19. It's 360 ohm resistor paralleled by 0.01 uF disk ceramic, inserted in series with the ground end of RFC1.

5.  Hot-switching TR relay

This mod is somewhat messy and of my invention. Having already substituted a diode for Q12 and removed R67 as in mod 2 above, unsolder the end of 4.7K resistor R64 which connects to point W and bend the resistor vertical. Mount a 2.7K resistor vertically with one lead soldered into the R67 hole which connected to the base of Q12. Mount a 0.47uF mylar capacitor vertically with one lead soldered into the R67 hole which connected to ground. Next, above the board connect the two resistor leads and the capacitor lead together using insulated wire to avoid C92. Finally, on bottom solder insulated solid wire from the Q12 base hole to the vacant R64 hole next to point W.

6.  Frequency offset unlike filter

If the offset isn't close enough already, and if the rig doesn't have one of the RIT mods, a substitution needs to be made for C55, the 6pF disc capacitor at the VFO. If the offset is too great the capacitance needs to be smaller and vice versa. A 5pF NPO capacitor from Radio Shack worked better for me. Also worth a try are the Radio Shack small capacitor assortment, or better yet a small adjustable capacitor if you can make one fit.

A final note: if your HW-8 doesn't run well from a 12 volt battery, try using a higher voltage battery with a linear regulator to deliver 14 volts. (The matching Heathkit power supply produced 13.8 volts.)