EL34 A2 Cascode SE triode

[Wavebourn]

And we see another bump when the tube gives up being saturated, so the FET finishes the job. You can get such a way even more power increasing both B+ and the voltage on the control grid, to give more voltage for the FET to swing.

 

[Doug De Young]

When in the design phase I did increase the G1 voltage slowly until no additional max power was made. I also chose the operating point to preserve the el34 dissipation. I’m definitely sure more power is available from a hotter operating point and more grid voltage with a different tube. Like a kt88 for example. But for that I’d need a more powerful power transformer and bigger heat sinks on the FETs etc. My goal of 10w is ok for this amp I think. Maybe a more powerful version in the future? 🙂

 

[Doug De Young]

Next up is this Russian 6L6 the 6P3S. It was beyond it's max dissipation and drawing heavy G1 current. Still it did not reach 10W and left A1 operation at only 1.5W

I’m not brave enough to leave it in the amp long term.

 

[Doug De Young]

This Tube is a 6CA7, it's something like an almost kt88. It leaves A1 at a respectable 3.3w but ultimately is higher distortion than the el34 at 10w, 10%THD

 

[Doug De Young]

The kt88 was a surprise for me. It's over all performance is great. It makes it all the way to almost 4w before leaving A1 and is still only .2%thd at 4w!! At 10W its a respectable 6%THD

I may just run kt88s in this amp instead of el34.

 

[Doug De Young]

And finally, here is the kt120. It makes it all the way to 4.4w before leaving A1 and has the lowest 10w distortion at only 5%. Very nice.