simple microphone tube tester

A little background for the comment I wrote. I measured a few tubes one # tube measured very different between makes. This tube is used in an expensive microphone. People have tried other tubes of the same number in the microphone and IIRC had to try a bunch to find one that work well for noise and sound.

Others here Dale, Tim maybe more build capsules I pay attenting to their posts. I thought I might add a simple tester to help others understand something about tubes used in microphones.

I don't believe much of what I read on the web I test it if I can.

Most tubes were not made for microphones the only one I read that was was the AC701, not sure about anything at all with the VF14 so many different stories about that tube.

Look at the specs and curves then look at how most standard tube microphone circuits. They are at the very curved bottom of the curves.

I don't know about anybody else, but I'm enjoying this thread, though I don't have much of anything to contribute at the moment.

Gus, I did see in your first post that you needed to order some higher value resistors for your tester. I know 1 Gig is what people tend to use these days, but if you could use some nice small 75 meg I have tons. . .found them in surplus for almost free and bought lots hoping to play with some microphone stuff, largely based on what I've gleaned from posts by you and the other microphone gurus here. Then my job ramped up and I have no time, or I get home and just want to sleep. . .

Anyway, I'd be happy to send you a bunch of those to play with. PM me if you want. . .

Gus, although my tube knowledge is very limited, i appreciate threads like this very much. As i understood this is a very nice and DIYable tube tester that really comes close the mic's real life behaviour and this should be appreciated by a lot of people here - because there always was a lot of interest in tubifying mics and tweaking tube circuits and how to select tubes...and real life measuring and comparing should be a much better approach than 'buy the xx tube from brand xx' internet reading...
Throw stones at me if i got that wrong!
I always like your contribution to this board - for sure it's mostly far over my head...but this is what i'm here for: learning!

Thank you and kind regards,

Martin

I just measured a few more tubes this time ef86s. rp and operating points all over the place between different brands. In one brand the numbers shift a lot, it was like measuring fets(maybe I got a bad batch of this brand tube).

Now this should not be news to some.

I was suprised to see the tube in my VM1(I did buy it used so it might not have been stock) looks like a wing c with gold plated pins.

off topic: ef14 its good replacement for vf14?