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Re: Atma-Sphere class A OTLs

Posted by kurt s on December 29, 2006 at 21:18:40

In Reply to: Re: Atma-Sphere class A OTLs posted by Ralph on December 29, 2006 at 14:38:42:

"It sounds like you have built up a pretty serious custom amp- not too many people use HF to run heaters. Had you thought about building more of them for fun and profit?"

Yes, but then I think about how hard that would be and how much money it would drain me for a very small niche market. I really don't know why manufacturers haven't caught on to the ultrasonic heating for DHT's in SETs because A) it sounds better with a blacker background, and B) nobody wants any hum on even 110 dB sensitive speakers like I have. Also, it only costs about $100 additionally in parts to have this feature. Not bad for high-end SET amps of $5K or more out there. It's just lucky that 45's don't hum all that badly in the first place, but why have any hum?

(You know what's the coolest thing about ultrasonic heating? You use small ferrite toroid cores with 20 or so windings per side and you have an isolation transformer capable of delivering enough power to fully heat a 300B and have it floating properly. Nothing to it! The magic comes from the high frequency for making cheap tiny transformers to do the job. One power supply, one oscillator, one small class AB power amp (a power op amp might do) and two or more small isolation transformers.)

But also, one of the best attributes of my amp is that it has 01A DHT drivers which sound so exceptional there, and there's just no way of putting that tube into production because those delicate thoriated globe DHT's are only found used today. And it's not a good choice for a broad application anyway because the input sensitivity of my amp is now too low for most people. Thankfully, I designed my own phono stage with so much gain it more than makes up for that. But this is an all analog system.

For digital I go to my HT system. That's good enough for digital to me.

Kurt

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