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Nikolas Ojala 22nd June 2007 02:22 AM

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:

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:

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.

Nikolas Ojala 25th June 2007 03:53 PM

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?

Shoog 25th June 2007 04:54 PM

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


Klimon 25th June 2007 06:28 PM

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


Nikolas Ojala 25th June 2007 09:04 PM

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.

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