thanks guys, i'll look into those models and links when i get a chance. i'm hoping to be able to learn a lot more about valve amps this way. apart from a few odds and ends it is hard to find out how they *really* work off the net.
porl ps. (offtopic): anyone know the approximate b+ voltage i should using for a SE 6v6 amp through a 4k primary? i built one from odds and ends (i seem to like that phrase) and my valves started glowing blue... looked cool though ;) hehe On 19/06/07, Dominique Michel <[EMAIL PROTECTED]> wrote:
Le Mon, 18 Jun 2007 21:59:25 +0200, "Giuseppe Zompatori" <[EMAIL PROTECTED]> a écrit : > In general there seem to be a lot of problems in simulating the power > section of push-pull NFB enabled amps in LTSpice... the NFB starts > oscillating producing really high frequencies even at modest volumes > eventually inflating the sim duration to infinity... garanted that's > also what happen in reality but only when the power section is > severely distorting... > The problem here is not the simulator but the valve models. Most of them don't modelise the grid current or have a very very poor approximation, they have a poor approximation of Ig2, they don't modelise the variation of the valves characteristics when Ug2 is changing, and they have a very poor approximation of the variation of the valves characteristics when Ig2 is changing. According to the data sheet, some tetrodes can get 2 watts on the command grid at full output. That implies huge grid current. At the same time, we will get huge Ig2 variations and Ug2 will drop (even with fixed Ug2 bias) because the voltage delivered by the power supply will drop at full output (around 100V drop on some peavey amplifiers!!! The saturation we can heard is for the half the saturation in the main transformer not in the amplifier or output transformer!!!). So, in short, don't expect a good or reliable result of a push-pull class B guitar amplifier with so limited valves model. And to simulate the whole amplifier is a must do, but without more reliable models, it doesn't make sens to try to optimize something with a simulation for that kind of electronics. In consequence, for me, and as long at we don't have better valves models, practical experiences are everything. Dominique _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/mailman/listinfo.cgi/linux-audio-dev
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