>>Is the power output ability in pure Class A not a linear function of number of tubes?<<
It should be, but there are several "classes" of Class A.
Pure Class A1 in triode has an efficency of 25% output power compared to the actual heat dissapated in the tubes - so to get 50 watts of audio you need to "waste" 200 watts in heat. A KT88 has a maximum rated anode dissapation of 40 watts, so would need at least 5 tubes to be safe, and that's not possible in a push-pull amp, so 6 would be a minimum.
But some manufacturers care about reliability as well as advertised power output, so may use more tubes than absolutely needed so as to run the tubes at (say) only 75% or even 50% of their maximum ratings.
This lowers the temperature in each tube and promotes far longer life.
But using the tubes in ultalinear or pentode/beam tetrode mode will increase this efficiency to around 50%, so you will get about double the power with no more tubes.
Realise, not all manufacturer's are 100% accurate/truthful when they call an amp Class A, maybe it's Class A up to a certain point and shifts over into Class AB something when pushed hard. So you might get a higher power rating for a given number of tubes from them.
Caveat Emptor...
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>>does Triode mode mean Class A by definition<<
No, there is no connection. Triode mode normally refers to pentode/beam tetrode tubes (e.g. EL34/KT88) wired as triodes as disticnct from real triodes (e.g. 300B, 845) and they can run in any class, A, AB, B, or even C.
>>, conversely, does Pentode mode mean AB?<<
No, pentode means pentode operation of a pentode (e.g. EL34) tube. A pentode can also be run in any class.
> Is Ultralinear the same as Pentode? (eg Manley Stingray and TAD 1000 have Ultralinear/Triode modes<<
No, ultralinear is a circuit topology where the screens of the pentode or beam tetrode output tubes are connected to a tap on the output transformer, giving (it is claimed) the sound and characteristics of triode with the power of pentode. It is easy enough to even have a three way switch that can actually change from pentode/tetrode output to ultralinear to triode mode in a EL34/KT88 tubed amplifier.
Each variation will sound different, personally I only like triode mode, (or real triodes) but that's my preference.
Regards, Allen (Vacuum State)
It should be, but there are several "classes" of Class A.
Pure Class A1 in triode has an efficency of 25% output power compared to the actual heat dissapated in the tubes - so to get 50 watts of audio you need to "waste" 200 watts in heat. A KT88 has a maximum rated anode dissapation of 40 watts, so would need at least 5 tubes to be safe, and that's not possible in a push-pull amp, so 6 would be a minimum.
But some manufacturers care about reliability as well as advertised power output, so may use more tubes than absolutely needed so as to run the tubes at (say) only 75% or even 50% of their maximum ratings.
This lowers the temperature in each tube and promotes far longer life.
But using the tubes in ultalinear or pentode/beam tetrode mode will increase this efficiency to around 50%, so you will get about double the power with no more tubes.
Realise, not all manufacturer's are 100% accurate/truthful when they call an amp Class A, maybe it's Class A up to a certain point and shifts over into Class AB something when pushed hard. So you might get a higher power rating for a given number of tubes from them.
Caveat Emptor...
------------------------------------------------
>>does Triode mode mean Class A by definition<<
No, there is no connection. Triode mode normally refers to pentode/beam tetrode tubes (e.g. EL34/KT88) wired as triodes as disticnct from real triodes (e.g. 300B, 845) and they can run in any class, A, AB, B, or even C.
>>, conversely, does Pentode mode mean AB?<<
No, pentode means pentode operation of a pentode (e.g. EL34) tube. A pentode can also be run in any class.
> Is Ultralinear the same as Pentode? (eg Manley Stingray and TAD 1000 have Ultralinear/Triode modes<<
No, ultralinear is a circuit topology where the screens of the pentode or beam tetrode output tubes are connected to a tap on the output transformer, giving (it is claimed) the sound and characteristics of triode with the power of pentode. It is easy enough to even have a three way switch that can actually change from pentode/tetrode output to ultralinear to triode mode in a EL34/KT88 tubed amplifier.
Each variation will sound different, personally I only like triode mode, (or real triodes) but that's my preference.
Regards, Allen (Vacuum State)