Simple OTL amp driver with EF86/6SN7

[Koonw]

I have built 6SN7 version of this driver but the gain is only about 6, so I add a front end gain stage of 6SN7 cascode. This EF86 driver has a gain of 60 so no gain stage is required. A small signal is taken from output connected to the base of LM317 CSS to balance driver the upper and lower tube. I like the unique sound of 6SN7/6H8C esp zero feedback, I'm not sure how EF86 will sound like. Those who has built Tim Mellow OTL amp can comment. Can use other tube of your choice with bias readjusted. Would you build the driver/amp?

 

[NickKUK]

I'm looking at the noise and harmonic dB levels..

 

[NickKUK]

Why run caps on the PP grid leaks or are these RC snubbers? (above TP2 and TP3). C6 and C7 seem quite large at 0.47uF.

Have you tried a bode plot through it?

 

[Koonw]

No, they are probe 0.1u and 10Meg resistor, Test Point (TP) to display AC components only.

 

[Koonw]

Freq. response curve, I change to 0.22u there is no significant change.

 

[NickKUK]

Freq. response curve, I change to 0.22u there is no significant change.

That's what I thought, most amps are ok with 0.2-0.3. Looking good.

I have a very similar OTL in progress. A cascoded 12BH7A with ecc99 backend. The only real differences are (a) I'm running a tube CCS andI have a driver section in front of the output triodes.

 

[Koonw]

100 Amplifiers – Part 3 , 1955 – 59 | Lilienthal Engineering
I have another version using balance drive based on Bootstrapped method. However I found the bass is too hard or heavy so I tried the current version using LM317 CSS balance drive. You can see I use PF to feedback the cascode stage, not to increase the gain but to increase the output Z (improved damping factor) as well as distortion to 1/2 compared when with no PF. You can try it, sound improved, it becomes thicker and better articulate as a result.
If you have built Bootstrapped or LM317 balance version let's know how it sounds.