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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
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
11,931 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.
jond's avatar
jond
5,893 posts
 
Charles you are so right so many roads and they are all valid. I lucked into mine, acquiring my amp because it sounded good, not at the time really truly understanding what went into its design. Now that I know more I am still enthralled by the sound and appreciate my amp even more. And agreed on power supply and transformers both should be high quality and overspeced.
normie57 OP
50 posts
 
Thank you all for your input!  Agreed....many roads to Rome or great sound.
I'm considering a VAC Sig 200 IQ stereo unit using a total of 4 KT88 delivering100 Wpc in class AB1 or AB2, or a Zeso Bia 120 stereo unit, also using 4 KT88, delivering 60 class A Wpc.  Both are in the $12,500 to 14,000 range.
Your thoughts and preferences would again be appreciated.  
charles1dad's avatar
charles1dad
10,250 posts
 

I can say that both of these amps represent good examples of high quality push pull tube design. The VAC has the well earned high status allure. I've heard the less known Zesto Bia amp and thought it was exceptionally good sounding.

Charles

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