6BQ5pp DC Power amplifier IVC （電流伝送入力+pp差動出力)

After getting successful result of 6C19P Power IVC, I wanted to apply 'single tube drive' method to 6BQ5 differential push-pull power amp. The hint to get complementary two drive signals from single tube circuit is given from Hybrid Power IVC amp in MJ Audio Technology (Vol. 2016 Oct.) written by Mr Kaneta. He says in this article that "The feature of Single tube drive is not only its simple circuit but also is more natural quality of the sound". ■Circuit design Only a half unit of duel triode 6DJ8 is used as first stage driver. Cathode voltage of the 6DJ8 is controlled by injecting variable current signal from 2SA970 so that one of grid voltage of 6BQ5 is maintained. This stabilizing circuit is called as ABC (Automatic Bias Control) in Mr.Kaneta's design. The +90V power is supplied through regulator. ■Simulation The simulation shows reversed phase drive signals for 6BQ5 are obtained from two 2SA606. The actual circuit is made on universal PCB. Below is 30 minutes record with data logger of grid voltage of two 6BQ5. The ABC should be working fine to get stable operating point. The first impression of the produced tone from this amp is similar to one from 6BQ5 single power amp. Not so strong driving power, but clear and precise sound. Its loud sound will not be stress to the ears. The music from the speaker is vivid and natural. Single tube drive produces very remarkable result.