P-P Load Resistance vs AB1 vs AB2

[rsumperl]

Good evening and a Happy New Year to all,
I am looking at a 2E26 data sheet which has parameters for class AB2 audio service. Given the same plate voltage and screen voltage, will the P-P Load Resistance change for class AB1?

Thanks
Ray

 

[BinaryMike]

Just by eyeballing a load line on the curves for G2=160V, I guess the best you can do in class AB1 is about 17~18W into 14K, or about 24~25W into 10K with G2=200V. Both estimates assume 400V on the anodes. Why not use class AB2? Tube linearity is no worse, and grid drive is easy with MOSFET source followers.

 

[rotaspec]

Check out Pete Millett's web page. He has experimented with 815 tubes in AB2. As far as I know, the 815 is simply two 2E26 in the same glass.

 

[Miles Prower]

Good evening and a Happy New Year to all,
I am looking at a 2E26 data sheet which has parameters for class AB2 audio service. Given the same plate voltage and screen voltage, will the P-P Load Resistance change for class AB1?

Thanks
Ray

The load will change significantly. Look at the plate characteristic. The v_GK= 0 plate current isn't above 150mA. It's much higher when going AB₂ and that means the load resistance decreases.

This type is a Class C RF type that was designed to have a very low static plate current with v_GK= 0 to reduce the bias required to pit it into Class C. As such, you're not gonna get much output if you stick with AB₁.

You can get 50W and more from types like the TV HD finals while staying in Class AB₁. There's also no telling what these sound like, and may need help from local + gNFB to sound really good. That's not the cae with TV HD types. There are better audio finals.