Head-ups for fans of AricAudio designs. His new Super 211 SET two chassis amplifier

Why do they use SRPP input stage and EL34 driver?

"Why do they use SRPP input stage and EL34 driver?" This is simple. Out of all of the other stages I experimented with- these simply provided the best drive, lowest output impedance, and best blend to the 211 power tube. The SRPP can drive the EL34 (in Triode mode- which is much different than Pentode, or UL mode as the drive requirements go up). The EL34 in Triode mode can provide the necessary swing (200V P-P) to drive the grid of the 211, and the low output impedance overcomes Miller Factor (capacitance at the grid of the next stage). It also has excellent linearity in Triode mode! This overcomes slewing, lack of headroom- and most importantly- the driver stage running out of steam before the power tube is in A1. This results in headroom, full frequency response and maximum power output. I hope this helps! Aric

Hey grannyring,

With your taste for well built artisan pieces of gear, you will get a kick out of what Aric has done in the design and construction of this masterpiece of an amplifier. Hope you get pictures of the inside soon and one day get to hear this piece.   

Hi @aricaudio ,

Thank you for reply.
I know that some designers use 300B tube to drive for 211.
300B is even more linear and transparent, but it is much more expensive than EL34, and not everybody like 300B sound signature. EL34 should sound faster.

I never tried SRPP input stage. In my 300B DIY amplifier I use single half of 6SN7.
But I have 6F6 driver in triode mode. And 6F6 is more easy to drive compared to EL34.
I heard 6SN7-6SN7-KT88 SE amplifier and it sounded very slow. One half of 6SN7 is not strong enough to drive KT88.

Regards,
Alex.

Hey Alex- no problem! Two things with DHT’s that are harder to overcome than with Pentodes are C Miller and also grid current. Most of these tubes aren’t linear unless you can drive the grid positive with a high voltage swing. Otherwise the top and low end suffers and is what most people think when they refer to a 300B (or other DHT) as "woolly in the bass", or "lacks high end sparkle but the midrange sounds great!". That’s where C Miller has its effect is on the frequency extremes. A 6SN7 cannot drive the 300B’s grid into A1 unless it’s in SRPP mode or is direct-coupled. It can still sound good but you’re not hearing the 300B’s full potential. On the KT88, I assume the 6SN7 stages were cascaded? In that case, I can imaging how two coupling caps and two stages could bring too much of a harmonic structure to the sound and become dull and lifeless. However if two stages of 6SN7 were configured in Mu Follower, Cathode Follower, or SRPP you could benefit from the lower output impedance to "swing" the grid of the KT88 better and avoid the overly complex harmonic signature. Best, Aric