mnewport said:I've been trying to find schematics for an ultralinear pushpull
amplifier that puts out roughly 30-40 watts in class A...I haven't had much luck finding one. Any suggestions?
Also, any recommendations for simulation software for tube circuits?
Such amount of class A power is quite a hard Job for most known power pentodes. 30W class A UL amp could be built with a pair of 6550 tubes.
Indeed, the most powerful and efficient power pentode is EL509.
A pair of these tubes can easely deliver about 40W of class A power, and moreover, the power will continuously increase with lower load resistance due to great reserve of output power.
Indeed, the use of conventional UL output transformer with screen taps will be unappropriate, because thses tubes require the Eg2 much lower than Ep. There is more efficient and versatile solution, the cathode feedback or distributed load circuit in which the small part of the primary winding is connected to the cathodes providing local voltage feedback. Such circuit topology can give ultimate results with any pentode and with either PP or SE, because one can freely choose the screen voltage, and the local NFB introduced this way is enough effective to get the same or even lower Ri than that for these same tubes triode connected, and the driver voltage will be still within reasonable limits. Also the proper choise of Eg2 makes it possible to alter the harmonic distortion spectrum in such a way that the high-order harmonics will be almost totally cancelled for the most part of the dynamic range, and the amplifier will behave much the same with different lads and when leaving the class A current range.
The historically first use of such topology seems the Quad II amplifier.
You can find more on the performance of CFB PP ampliers with EL509s at www.cortmi.com.ua/omak
Tube Addict said:Look at www.amplimo.nl (dutch site) for the UL40-S2 designed by Menno Vanderveen, or look at www.plitron.com
The UL40-S2 has an ultralnineair schematic. standard with svetlana 6n1p/EL34. I build it with Svetlana KT88's.
It has a lot of class A power and sounds great. A lot better than the Audio Innovations series 500 i had before...
If you need the schematic, let me know..