Modern version http://www.babeland.com/hitachi-magic-wand/d/2487
Sent from my iPhone On Sep 21, 2012, at 5:18 PM, Alan McKinnon <alan.mckin...@gmail.com> wrote: > On Fri, 21 Sep 2012 15:52:17 -0400 > Michael Mol <mike...@gmail.com> wrote: > >> On Fri, Sep 21, 2012 at 3:45 PM, Alan McKinnon >> <alan.mckin...@gmail.com> wrote: >>> On Fri, 21 Sep 2012 15:25:49 -0400 >>> Michael Mol <mike...@gmail.com> wrote: >>> >>>> Guys, this fell into politics, one of those categories of things >>>> you don't discuss in polite company. Not that I'm accusing anyone >>>> of being polite, >>> >>> Phew, glad to hear that last bit. You had me worried for a second, >>> what with my reputation to uphold and all >>> >>> >>>> Now, could we go back to discussing software, packages, electronics >>>> and amplifiers? I found that portion of the thread utterly >>>> fascinating... >>> >>> That's a good idea. Would you like to hear about Hitachi Class H >>> amps? >>> >>> I'm forever fascinated that I seem to be the only person that ever >>> heard of them. Most techies know A, AB and B. Some know Class C but >>> I get blank looks everywhere I mention Class H... >> >> I would indeed. And a primer (or reasonable reference for someone with >> just a technician's amateur radio license) on class C. :) >> > > IIRC this was back in the late 70s or early 80s. Someone at Hitachi > figured that amps (like code) spent 90% of their time doing 10% of the > effort. If you had a 100W amp, it wasn't trying to drive 100W into the > speakers all the time - only when the input signal was large enough. > > And yet, the power source for the output stages was permanently running > at 70V or so (that's what it takes to get 100W into speaker coils back > then). A transistor isn't a perfect isolator when biased off, so some > of that voltage gets dropped somewhere (across the output transistors) > and the result is a lot of wastage. > > wikipedia has a quite good summary of the usual classes - A, B, AB, C & > D: > > http://en.wikipedia.org/wiki/Electronic_amplifier#Class_C > > But, Class H. A Hitachi engineer had a brilliant idea: > > Run the damn thing class A all the time (for the audio quality) but at > around 24V. Heat generated is minimal. The power supply had a fancy > voltage tripler circuit and when the input warranted it, the supply > voltage would (very rapidly) switch over to the full 70V and the amp > would deliver the full rated output. There was fancy circuitry in place > to avoid distortion at the switch on point of course, but that is a bit > OT. > > An interesting take on the problem. Mechanical engineers do this all > the time with engines - turbos only kick in when you need the power > boost they provide, the rest of the time the motor is in regular mode. > > I've promised myself for years since my apprentice days that I would > one day built a valve amp from a kit. There's something about the warm > glow from the tubes on a winter night that is appealing :-) I'd better > hurry up and get on with it, I read that decent quality valves are > becoming scarce and are generally only available from (what used to be) > the USSR. > > > > > -- > Alan McKinnon > alan.mckin...@gmail.com > >
