Like all the other stages of the transmitter, the driver amp is run in class A. Shunt feedback and emitter degeneration is used to ensure good linearity and wide bandwidth. The transistor is a CB output transistor. The 2SC2216 or 2SC1306 should also be suitable. The standing current is just under 500mA so a good heat heat sink will be required. The input transformer is 8T/2T on a pair of high permeability ferrite cores. The output transformer is 4T, bifilar wound on four ferrite cores.
I have received some very complimentary reports
about the transmit audio quality, even from the 'audiophiles' on 40M. The spectrograph
above shows the results of a two-tone test. The 3rd order (A) and 5th order
(B) intermodulation products are clearly visible. All IMD products are 40dB
or more, below either tone. This is equivalent to 46dB below PEP. There is no
trace of IMD (splatter) at +/- 3KHz, when listening on my other receiver. The
circuit was tested at an output level of 2W.
Test Wav file.
