mbj335 a écrit :
Attention il ne faut pas confondre single ended et class A...l'ampli peut très bien être en push pull et en class A...le push pull permet de sortir les 18 watts alors que en single ended c'est 11-12 W max !
Donc je pense que le 1974x est en push pull class A (et les clones aussi).
Des détails ici :
http://www.diyaudio.com/forums(...).html
je suis désolé mais je ne vois nulle part écrit qu'un push pull EL84 en classe A peut sortir 18W
Je cite :
Citation:
Marshall have never described them as Class A.
Many people seem to refer to any cathode biased output stages as Class A which is not accurate. Two EL84s in push pull could only deliver a max of 12 Watts in Class A and that's with 10% THD.
You could get 17-20 Watts from 2 EL84s in Class AB depending on the HT used
Citation:
Two EL84 in push pull Class A = 10W, Class AB can deliver about 17/18W for the same two valves. The Marshall 1974 delivers 18W from two EL84s in Class AB.
Citation:
The significant difference in sonic quality between "single ended class A" and "push pull Class A" by commercial devices is in my opinion due to the fact that the so-called "push pull Class A" in real life is often push pull class AB. Just because the area where will be leaving the Class A mode, is a little above typical values arround 30 to 50 mA (e. g. 100-300mA), some manufacturers already believe that they offer "pure Class A" amplifier.
et le bon vieux wikipedia :
Citation:
In common with all 'E' prefix tubes, using the Mullard-Philips tube designation, it has a heater voltage of 6.3V. It is capable, when used at its plate rating of 300 volts maximum, of producing 17 watts output in Class AB1 in push-pull configuration. Many guitar amplifiers routinely run EL84 tubes in excess of 400VDC, with the Traynor Guitarmate reportedly putting out 25w RMS with 2 EL84's in a push pull configuration and a B+ between 400-420VDC.
