SE amplifier - How much power?
 

I have been thinking about a design and construction of two identical single ended class A no feedback tube amplifiers for eight inch full range drivers. But I don't know yet, how much power the amplifiers should be able to produce. I have some beam tetrodes and HF triodes available, so I thought about using them. I also got impressed about the Ankoru amplifier by Andy Grove (Sound Practices issue 12, 1996). I like his design philosophy, although Ankoru is much bigger amplifier than I need.

I also found this:
http://t-linespeakers.org/tubes/triode-trick.html

I could use that idea with the beam tetrodes. I would use resistors instead the zener diodes and bypass them with bigger capacitances.

This is the question: How much power is enough?

I have a pair of Goodmans Axiette 8 inch drivers:

http://nukku.net/no/Axiette101-a.png
http://nukku.net/no/Axiette101-a.gif
http://nukku.net/no/Axiette101-b.png

I have also a pair of particle board enclosures. Someone had designed them to be bass reflex and for bigger drivers, but those boxes are big and I like more closed box than bass reflex. I measured the inside volume, which seems to be 86.4 litres (3 cubic feet). The holes were cut obviously for 10 inch woofers. I think I'm going to fill the volume with polyester wool, to get maximum damping.

Ok, any input is welcome.

Another configuration and question about Watts
 

How about two EL95 pentodes in a push-pull ultralinear setup? I could get approximately 7 Watts output. Yes I know it would be no more SE or no feedback amp, but I just have plenty of EL95 tubes too. It seems that anyway I must wind the transformers by myself.

According to specs the voice coil of Goodmans Axiette should withstand continuous 5W power. Would 7W amp be fairly big enough, or should I leave more margin for peaks? Those Axiettes are so low power drivers that a possible accidental burning worries me.

Should I design the power supply so that it could give peak power much more than 5W, but continuous power no more than 5W?

The transformer should protect your valuable drivers from burn out. This is one of the great advantages of valves over SS.

Shoog

I wouldn't worry about it, your ears will fry long before the axiettes (unless maybe if you live outdoors:))

Simon

5 Watts Peak A.C.
 

I read again the little paper I found from the Goodmans Axiette package:
Maximum power handling 5 Watts Peak A.C.
and the same text was printed also on the box.