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RE: EFB

I wasn't aware there had been failures, and I haven't analyzed the circuit except in a general conceptual context. Three things to note...

First, Dave hasn't been able to duplicate the failures. That's a big problem, because it leads to revisions that may or may not be relevant or effective. For all he knows (and I'm sure he would agree), it's possible every one of the failures was due to the use of counterfeit parts from China that were purchased through disreputable sources such as eBay or Amazon.

Second, recommendations in the datasheet regarding protection diodes and decoupling capacitors should be all that's required to fully bulletproof the IC. I've designed quite a few Vregs and applied three-terminal regulators in a wide variety of applications. When it comes to these decades-old devices, the manufacturers pretty much have it nailed. Although I frequently refer people to Dave's site, I would never use the LM337 myself without following those guidelines.

Finally, the filaments should be elevated using their own voltage divider from B+, regardless of the method used for output tube bias. This not only eliminates the issue Dave theorizes regarding damage to the regulator, but allows raising the differential to a level more likely to provide the desired benefit.











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