Heathkit HW-9                                 back to start page

I built my HW-9 in 2008, about a quarter century after released by heathkit. A friend gave me an unbuilt kit he bought years ago. He had not the time to put it together.

Building was fun. The trx worked immediately, but a number of problems appeared. Many have already been discussed by others.

Problems:

1. the VFO cap and gear were constructed in a shaky an unprecise fashion. A new, more precise VFO gear and rotation-stable attachment of the VFO cap at the upper PCB board solved this

2. there was severe feedback oscillation in the IF amplifier. This required to largely re-construct the VFO design beween mixer and the MC1349 stage. I also included a 500 Hz CW filter.

3. AGC delay was much too fast. An increase of the AGC cap solved this. This slightly increased the AGC attack time, but this could be tolerated.

4. The final amplifier worked fine when the HW-9 was terminated with a dummy load. However, termination with an antenna tuner with more complex impedance often caused severe oscillation. This has also been reported by others. It could be improved by exchanging the transistors of the driver stages. Nevertheless, I plan to replace the PA by a more stable design.

5. The switching diode at the antenna input generated a lot of noise when operating on crowded bands, such as 40m. I replaced it later with a pin diode.

Other modifications will follow...