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In Reply to: RE: LM317 Failure posted by DAK on January 23, 2016 at 22:48:16
I'd like to see the circuit you're using around the 317 before making a recommendation. Can you post it?
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Buy Chinese. Bury freedom.
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Here is a link to the website. http://rh-amps.blogspot.com/2013/01/rh-universal.html
BTW, I wrote Alek and he explained that the lm317 needed a heatsink. I did not realize that and consequently left it unfettered. But, in the amp the chassis I used is unventilated and I am not sure if even if the lm317 were heatsinked if it would have survived long term.
Well, ambient temperature does play a big role in all this. As you say, if the temp is too high, even a heatsink might not help much.As a side note, Have you considered using a voltage regulator instead? That would allow you to more easily adjust bias from tube to tube. The "enhanced fixed bias" scheme was originally designed for push-pull, but it should work for SE as well. Here's a representative schematic:
About protecting the LM317 from excessive voltage, a TVS (transient voltage suppressor) acts like a Zener, but has a much steeper knee. It would be connected across the LM317 with the anode to ground and the cathode to the "IN" pin. A device rated for 28-30V should work OK.
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Buy Chinese. Bury freedom.
Edits: 01/24/16 01/24/16
and it died after less than 100 hours. That ic was mounted on the chassis with a proper insulator. So, for higher powered applications, I am not convinced that a transistor is as reliable, and I mean as bulletproof as a suitable resistor. If one is building an amp for someone I would think that would be the standard to achieve.
I'm pretty confident about applying analog ICs to control vacuum tube circuitry. However, they need to be protected in ways that wouldn't be necessary in their native environment. The user has to examine all the possible "what if" scenarios for potentially failed parts surrounding the IC and look for ways to prevent those failures from exceeding its ratings. This is all more trouble than it appears at first glance.
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Buy Chinese. Bury freedom.
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