GU-50 + solid state driver

[SpreadSpectrum]

convinced that tube drives tubes better than sand ?

I'm not sure you can justifiably draw that conclusion based on this particular experiment. The correct conclusion here is that these tubes drive the output stage better than an op-amp with inadequate supply rails.

 

[ballpencil]

I second that. I doubt OP would come to that conclusion had he been able to try UL or triode connection on the output stage, despite the SS driver.

 

[stocktrader200]

I used 12AX7 > 2n5551 Concertina > 6922 & BJT supertriode > output Transformer
no global feedback Best amp I've heard.
You also get 25 - 30 Watts from a 160v B+ supply.
200v mosfet also works great for concertina
I found SS gain to be somewhat harsh when used instead of 12AX7