ESL OTL amp - simulation help

[Filip4]

Hi, I am newbie in tubes and I need some help from you guys.
I use a schema from J. Broskie, but when I am doing a frequency response, I can see some problems. Since it is without feedback, I took the curve directly from the output, but I do not like the phase shift. Is this okay? Or should this be compensate to have phase margin at least 60 degrees?
Thanks for help.

Schematic:


Frequency response:


Original schematic:
The Tube CAD Journal, Electrostatic Headphones

 

[rayma]

I took the curve directly from the output, but I do not like the phase shift.
Is this okay? Or should this be compensate to have phase margin at least 60 degrees?

Phase shift automatically comes with the amplitude response variation.
Since you have no overall feedback, the concept of phase margin is not relevant.

 

[Filip4]

Thanks, but what if I add negative feedback? Amp si running better then, but I was not able to get open loop gain plot. I am doing something wrong I guess (Add voltage source between R24 and output from U3 and took plot from these two points).

 

[rayma]

what if I add negative feedback?

Looks like -90 phase at unity gain, so it should be ok with nfb.