Rectifier Tube Concerns

[trobbins]

Wrt the youtube video in post #57, I noted what looked like a large NTC resistor on the mains input of the test amp. I also thought it confusing that the valve swapping tests were done with the rest of the amp powered and the output stage hot - as that just complicates any comparison as the video didn't show actual time delay and overshoot of B+ rise for each of the rectifiers from a cold start (especially as the video was full of cut/pastes anyway). It would also have been worthwhile measuring PT secondary voltage under at least the lowest and highest load scenarios, given that audio output power was being tweaked between rectifier tests. There was also a comment that inrush protection really should be used with an ss rectifier - imho that is not a good comment to make for those who don't adequately appreciate the situation, as it could entice some to add extra circuitry in a high risk location for no tangible benefit, as compared to the option of assessing the mains fuse.

 

[Sam Cogley]

And you really think a preamp, that's gonna likely draw less than 50 MA. from it's B+ supply, is going to flame a tube rated at 175 MA. ? We are still talking preamps here, yes? In a power amp I sure wouldn't use it, but I would have no reservations of using it in the Blue Velvet preamp that is the original subject of this thread......

I don't care what sort of circuit that it's in, using a 5V4G without installing the "pre-rectifier" diodes as recommended by dcgillespie is just asking for trouble. Just look at the size of the plates in any 5V4G vs. any 5V4GA. They're delicate, it's a known problem, and any of the fixes are easy. Why risk it?