Modification of a Chinese KT90 PP amplifier

[FYC]

Recently I re-engineer a Chinese KT90 PP amplifier, using some interesting concepts presented in TubeCAD Journal. Attached file is a summary report of the process. Feel free to advise any comments.

 

[jane]

With 20W Class A, the output tube should be biased to 51mA..

Your class A calculations seems to be wrong.
Class A power output = Raa x (Iq/1.414)^2
That will give you 5W at 50mA quiescent current (Iq) looking into the 4k Raa OPT.

 

[FYC]

Thanks for point that out. You are correct. I hit some conceptual mistakes in making the calculation.

Well 5W is a bit disappointing. So far I have not run into any clipping situation yet but I need to watch to see if I need to bring up the idle current a bit. Seems that I have some room to bring it up to 70mA and shot it up to about 10W.