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Andre Jute[_2_] Andre Jute[_2_] is offline
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Default What is the most powerful audio output tube?

On Thursday, December 8, 2016 at 3:20:48 PM UTC, wrote:
What is the most powerful audio output tube, as far as RMS wattage
output?


There is a self-contradiction in this question. There are lots of really powerful tubes but they aren't audio tubes; many sound like ****. There is, even today, plenty of choice in quality audio tubes that sound great, but they aren't necessarily all that powerful. In hi-fi, furthermore, it is accepted that you sacrifice some of the available power to operate the tube on the flattest part of its transfer curve, so that mitigates against hogging out all the available power. Also, the most refined audio sound comes from triode tubes, which are pretty inefficient, meaning you need lots or very big, not ones to make any appreciable power.

However, unlike some of the advice that you're getting here from people who've never built or heard a big tube amp, there are ways to get around it. First of all, you can parallel standard tubes like KT88 to your heart's content (well, actually the depth of your pocket, because the custom iron will cost plenty); I had a big OTL KT88 amp built as a modular rack mount system that by rewiring would give any output you wanted; it took up two bays; but it sounded like what it was, a PA system. Even the humble EL34 can build into a very potent amp: I got 96W of high quality audio sound out of parallel push-pull tubes running in class A/B with toroidal trannies in a stereo amp that two people could handle with ease, one with some difficulty; for home use it had 18W in Class A, so the massive oomph was rarely needed.

Next, some of the broadcast tubes sound fabulous, for instance the 845 broadcast triode, and you can parallel triodes in single-ended output for the finest sound of all, zero negative feedback SE, same as you can pentodes in push-pull. For instance, my 80W SE amps were deliberately operated at only a fraction of theoretical output to linearize the sound. I could as easily have chosen your 500W output if I were willing to sacrifice some sound quality; instead I put the time and the money into high-sensitivity speakers.

None of this throws up insuperable technical problems. The biggest problem of big amps is in fact the availability and cost of very high voltage connectors for the separate components, or the monstrous weight if you build the thing in one unit. For my 80W SE amp, Menno van der Veen designed the transformers for me, and Plitron wound them, and listed them for the intrepid. But it is long since broken up as too heavy, too hot, too large, too dangerous, just too unnecessary. The booster amp, 3.8W of SE 300B, with a bicor horn turned out to produce all the sound pressure I actually need. (A booster amp is a complete small power amp you use to drive a much larger power amp.) Don't laugh. When a sports field across the street from my house annoyed me with their unshielded PA, I coupled my 3.8W 300B SE amp and bicor horns to the stairwell in my four-storey town house, opened the front doors, and blasted their premier event of the year into incoherence. They scrapped the offending PA the next day.

***
If you're just building a humongous amp to prove you're a swinging dick, great, I admire initiative and balls and magnificent obsessions. But if you have a real problem to solve, like x sound pressure in y spatial volume, I suggest you redefine your need working backwards from the speakers: if your speakers are sensitive, a Bessel Array or bicor horns, the amp soon gets down to a practical size and electrical requirement and the costs start approximating reality as she is lived.

For a Bessel Array, try the brief introduction he
http://www.audio-talk.co.uk/fiultra/...n%20BESSEL.htm
And the smallest of my bicor horns looks like this inside:
http://www.audio-talk.co.uk/fiultra/...20T91HWAF3.jpg

Andre Jute