The first power amplifier for this transceiver project initially was capable to produce 20 watts of SSB pep rf power on the 20 meter band. The transistors in use are the 2SC1969 bipolar types by eleflow.com. A single device is rated to max. output power of 16 watts according to data sheet. In push-pull mode this nearly doubles because each of the semiconductors only has to amplify half of the duty cycle. Hence I started trying to get a little bit more power out of the PA assembly.
First I modified T3. The former data was: 1+1 turn primary center tapped and 4 turns secondary on a homemade pig nose core of 2×3 stacked FT50-43 toroids.
The new transformer has got 1 secondary turn more. Wire is 0.8mm enam.wire both for primary and secondary.
First I tried out 0.5mm enam. wire for the secondary which resulted in about 23 watts output pep. Next I used 0.8 mm diameter enam. wire which reduces the consequences of skin effect significantly . Penetration depth of a 14MHz ac current is only some 50 µm, thus every increase in surface area reduces resistance.
This set of measurements greatly improves two figures:
- Output power increases from 20 to 25 watts pep,
- carrier suppression improves by 5 dB.
The enhanced signal on the RIGOL DS1054 scope:
About 100 volts pp. (i. e. 35.5 volts rms) at 50Ω equals to about 25 watts pep. Nice improvement for a minor change that was done within 20 minutes!
vy 73 de Peter