Is it the 6SN7 or me?

[arnoldc]

Last night I played with TubeCAD (I'm lazy) cause I wanted to put my 6SN7 to good use. I configured it in SRPP mode given the following conditions: 320V B+, 8mA

According to the results, I'll get 11.29 Av, -3.9 bias, +-44V Vout

So I went ahead and ripped off the 6SL7 circuit from my 2A3 and wired in the 6SN7

I wire the lower tube's cathode with two LEDs instead of 470R resistor.

When I got to play the amp, I immediately noticed the lack of dynamics and resolution. It was disappointing. Boring sound

What have I done wrong?

I've configured this amp to use the Sun Audio circuit (2 stage 6SN7) but did not like it as well.

 

[EC8010]

LED bias works best when the anode load resistance is high - SRPP puts a quite a low load resistance on the lower valve.

 

[arnoldc]

aha, i'll change it to a 470R resistor and see what happens.

thanks

 

[Alastair E]

The 6SL7 removed from your amp has a higher Mu of 70 as opposed to the much lower Mu of 20 of the 'SN7.....

I prefer the sound of the 'SL7 to me, Much more dynamic...

 

[arnoldc]

Alastair, yes I was wrong. I thought that having a lower mu tube (I have a preamp) with much more current could improve the dynamics from that of the 6SL7.

I listened to it again last night and it was butchered by my 45 amp with 5842 as drivers.