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.
