10 watt amplifier for MF phasing exciter

Internal view, cover off - amplifier built inside old pc psu box

Bias circuit bottom left, antenna changeover circuit top right

In my last post, ( 2nd November ), I described the phasing exciter I made especially for data mode communications on the 630m 475KHz MF band. I have been using it for beacon transmissions and 2-way contacts. I tweeted news of one such contact using JT9 mode. All this has been achieved with an output power of just 100mW. For consistent results, however, particularly when propagation conditions are not favourable, ( e.g., long periods of fading ), more power would be beneficial. So I have built a single-ended class AB rf amplifier rated for 10W max output which is connected externally between the phasing exciter, low pass filter and antenna.
Once again I have used a metal box from an old pc power supply, complete with cooling fan, for the enclosure. A type 2SC3039 power transistor is fitted to a 5K/W heatsink directly in front of the fan. I have included a variable bias circuit, based on a 2SC2958 transistor; actually it's the same transistor type as the driver in the exciter as I had spares. I have used this to set the current for my chosen no signal operating point for the 2SC3039 for class AB operation.
The amplifier has made a huge improvement to the reception range of my WSPR signal; so far up to 1632kms.