7 type of vaccumtube amplifier. 6AW8A is the best tube to the audio amplifier of amateur radio. 38dB is best gain of all the circuits. 390mW is enough power.
6BM8 is very famous as a audio amplifier. 30dB and 300mW is good performance. But 6BM8 need 0.78 ampere for its heater. It is about two times than 6AW8A. If I could supply more high voltage for plate,it would indicates more performance.
6FQ7 is similar vacuum tube as 12BH7A. We can enjoy the triode-output-sound by them. 140mW is enough power output. Please remember that the transistor radio has about 100mW. But 6FQ7 is middle myu- triode, and therefore voltage gain is not so high as another tubes. Total-gain of this circuit (11.3dB) is not enough for normal radio.
12BY7A has very high gain. It’s gm is 11m-mho. Therefore this circuit has +9dB gain, including the loss of output-trans,only by single tube. If you can stay some proper voltage amplifier in front of this power smplifier, you can use 12BY7A as power amplifier, better than 6AR5.
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