Triode vs. Pentode

Thanks for your thoughts, Trelja. I'm quite satisfied with the way the system sounds with the VAC in pentode mode, but I was/am curious to hear what triode could bring to the party. I think I'm going to stay put with my equipment at this stage. If I have an opportunity to audition a CD player with volume control, I'll certainly try CD direct to hear what differences that might entail.

To my ear, pentode gives me the impact on the head of the bass drum, while the triode pulls me into the middle of the tone. Pentode offers punch, while triode is seductive.

Just my 2 cent ears...

"Pentode" means that an extra grid in the output tube is being fed with a signal taken directly from the transformer secondary winding. This is "corrective" (negative) feedback for distortion generated by the output transformer. This is why the amp can deliver more power before distortion becomes excessive.

If you do not listen very loud, and your speakers are efficient, the power delivered in triode mode will be sufficient. Distortion will be higher than the same power in pentode mode, but the harmonics generated by tube amps are not unpleasant, and you may actually prefer the distorted sound.

So, the "best" mode probably depends on the kind of music you are listening to, and how loud you want to play it. Feel free to switch back and forth.

My Mesa Baron, which has triode/pentode switches, sounds more clear and open in triode for all acoustic and most smaller scale works, but pentode power helps in the base and is better for loud rock etc.

Hello Tvad. I think Trelja and the others here painted the triode/pentode mode picture in the proper perspective here. Speaker efficiency as well as the impedance load the amplifier will see can also have a profound influence in ones mode of operation as well. I have a pair of el-34 based vac pa90-c monos that output 90 watts in pentode or 45 watts triode. However,I used the genelex kt-77 for output tubes[a beam power tube like a kt-88]as opposed to the el-34 [ a pentode] to drive 98 db efficient Tannoy Westminsters. In my case, I personally preferr the triode mode no matter what music type I'm listening to. They are more focussed and transparent in triode mode and just sound tighter in my rig.