Nik VK4PLN has been doing further work on upgrading the linear amp to Mitsubishi finals in his µBITx. He says,
“So looking good so far. I am getting these output values: (RV1 adjusted(75%) for 20W on 80/40)
80m : 20W
40m : 20W
20m : 18W
15m : 17W
10m : 14W
“No feedback, but I have yet to test a QSO on 20/15/10m…
The configuration is:
- BN42-202, but a 2:4 ratio winding giving 1:4 transformation.
- 320pf on all 7 emitter resistors of the pre-amp chain
- 330pf across the primary of the final’s winding.
- 220 ohm feedback resistor.
The finals run cool at 20+w with 330pf Mica cap. Nik is still considering changing out the driver and pre-driver transistors.