Taking on-board the test results to date the latest iteration of the 1 watt amplifier has the following characteristics:
- 1 Watt output
- 2SC3356 > 2SD1664 > 2x 2SD1664R in Parallel
- First two stages use a bifilar transformer to present the collector with 200 ohms for increased gain.
- Use of resistors to provide a thermal bridge to ground for heatsinking.
The results of my experiments have overturned my previous position. You do not need a working RF transistor, suitably rated, recovered from another radio to build 1 watt Class A HF amplifiers. 1W HF amplifiers can be reliably made using many of the general purpose transistors available that cost a few cents each.
If there is sufficient interest I'll put together a kit. My back of the envelope estimate is the cost would work out around US$5 for a PCB with all surface mount parts fitted.
Save those working RF transistors for more demanding applications!
73's
Richard
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