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How do tube manufacturers like VAC get 55 watts per KT88 where others get only 30-35?

Just wondering how some push pull tube manufacturers like VAC and others get 55 watts per KT88 tube while others are more in the range of 35? Does driving a tube hard like this have any ramifications as to distortion, sound, headroom and tube life? I know VAC amps are highly musical so design, power supply and output transformers obviously contribute much to overall sonics. A company like Zesto gets about 25 watts per KT88 but uses a class A push pull circuit rather than class AB.  This seems like an attractive design.
I guess, as always, it's all in the implementation. Thank you for helping me to better understand.

normie57
mid40sguy's avatar
mid40sguy
163 posts
 
Kevin Hayes of VAC has stated in part it's due to the output transformer design. Lovely sound that's a fact.

jond's avatar
jond
5,852 posts
 
Topology and Class have a lot to do with it as well, Pentode vs Triode and Class A vs Class AB. A case in point my own amp uses a pair of El34’s per side and puts out 17 wpc, you see other El34 amps with the same output  tube complement putting out anywhere from 25-40 wpc. My amp is triode wired and Class A, and runs the tubes conservatively. Pentode and Class AB with both give you more wpc, albeit with different sound characteristics.
georgehifi's avatar
georgehifi
10,312 posts
 
Many ways of using this tube, Tetrode Ultralinear,Pentode, Triode in push/pull mode, all with different wattage results.

Cheers George
charles1dad's avatar
charles1dad
10,250 posts
 
Jond, 
Agree, many roads lead to Rome. Personal preference for me is your amplifier design/approach.  Class A with conservative tube operating points and conservative power rating. These types of amplifiers with stout power supply and good output transformers consistently sound superb, 
Charles 
atmasphere's avatar
atmasphere
11,846 posts
 
If your KT-88 amp is only making about 35 watts, it could be because the power tubes are wired in Triode mode. This is done by tying the screen to the plate. Output power is reduced but so is distortion as the tube is a lot more linear in triode mode.

If the amp is class A and triode the output power might only be 25-30 watts.

60 watts is pretty common for a pair of KT88s operating class AB1. But its possible to get more power without going into AB2 operation although I would suspect that the VAC design with 450 watts is a class AB2 design.
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