Tube design

[Frank Wong]

Just finish reading the tube sticky!

Just to clarify with all things being equal & with efficient speakers is it good to go single ended running pure class A with no overall feedback?

 

[Palustris]

Well, as you are certainly aware, all things are never "equal." That said, I find the sound of a single ended triode amplifier coupled with a very efficient speaker provides very satisfying sound. I would suggest you research really efficient speakers first and then build or purchase an appropriate amplifier that matches it well. BTW: really efficient speakers are in the 100dB range. A 93dB speaker is not suitable for a full range with full dynamics SE amp in the 3W - 8W range that is typical for the 2A3 or 300B amplifier and even 96dB speakers are going to give you some compression on dynamic peaks.

Just to clarify: by definition single ended is always class A since there is a single output tube. You can add feedback if you wish: experiment.

Personally, I use the Zu Soul Superfly speakers. Notice that they are specified to be 101dB and also present a 16ohm load to the amplifier. The combination means that these speakers do exceptionally well with about 6W. It is amplifier dependent though. I tried my PP 6P14P amplifiers with the Dynaco output transformers for about 15W, and the upper bass was just not satisfying. I replace this amp with my SE 320B 6W amplifier and the missing bass became obvious. It is hard to know the reason why this is, as the PP 6P14P amp was "bass heavy" on my Altec A7 speakers which are over 100dB efficient.

Be prepared to experiment!

 

[gadget73]

A lot of that stuff is heavily vested in personal opinion. Some people tell you global feedback is the greatest thing since sliced bread. Others say its the best way to ruin good sound. There is no single answer, the right answer is usually whats best to your ears, room, and speaker combo.

 

[primosounds]

I use Altec 19 speakers which are supposedly over 100db efficient, with single ended pentode amps. That is running 6l6 , 6550, el34 or kt88 up to kt120 output tubes. I am using the RH universal circuit with fixed bias which easily allows me to adjust the tube's power dissipation, and thus try the different output tubes, by adjusting the cathode current. This design uses "local feedback" from the output tube plate to the driver tube plate, which has much less of a sonic impact than global negative fb. I find the sound quality from my amps are very nearly identical to a triode amp of the same output power.
So whether you choose a triode or pentode powered SE amp you really need to experience it for yourself and then decide if the millions of SE amp users just are deluded or have bad hearing. Which some of the PP topologists seem to say or imply.

 

[Frank Wong]

Thanks for the info guys. I am thinking of the Icon audio SE stereo integrtated running one KT150 per child in Class A 28 w ultralinear.

BTW with this topology will it surpass Pass Labs X30.8 solid state amp?