It seems difficult to get a twelve volt RF amplifier to work well on sideband at over 1.5kw.
The Texas Star DX1600 and 1600x work well up to around the 1-1.2kw PEP range but are getting pushed in their discomfort zone at much more. Doesn’t seem to much else out there at the moment and Texas Star were not interested in reproducing the 16 transistor DX3200 they once produced as they could not stand up to life in the real world and the return rate was close to 100%. The amplifiers use the Toshiba 2SC2879 device and as far as I know it is still the king of bipolar 12v devices.
Newer mosfet devices are emerging now with power levels approaching 1.2kw PEP per device but the cost is still quite high. The heatsink technology required to remove the heat generated by these small devices will also need to be further improved. While looking around we came upon a device that has been out for some time but has 3 times the power output of the 2879 but runs at 4 times the voltage..50v.
There seems to be a correlation between the IMD products and the voltage that a device runs on when using it in AB class to amplify at HF frequencies. Higher the voltage the better the IMD. The cleaner the amp…all other things being equal…
So if 8 2879’s can produce 1kw OK then 8 of these hi voltage mosfet parts should produce 3kw for the same footprint. Having 8 devices the thermal dissipation can be spread over a larger area of heat sink, but the associated components will be more and special combiners will be needed as well. When it is all said and done a decent tube amp will produce the same for probably less cost and work but I prefer to use solid state and DC. Personnel thing.
First thing was to find the power supplies. 57A 50v supplies are available on the used market. I bought 2 of them for US$135 plus shipping. They look like missiles. 2 feet long. I think they have come out of telephone exchanges. 2950w max output. Although one PSU should run the amp OK in SSB we will use 2 of them so we always have enough headroom…I am not building this ..it is being farmed out and the maker is plodding along slowly getting the parts assembled. he knows what he is doing and has the experience to carry out the job. At the rate things are going it will take a year but fortunately I am in no rush so “steady steady; catchee monkee”..(old chinese proverb!)
The transistors are the SD2933 devices. 8 of them. Looking for a relaxed 1.5-2kw PEP output.