Question about Tubes for a CJ (Conrad-Johnson) Pre-Amp

Kevin Deal has this to say about the Brimar 12AU7 on his website, "When I listen to these, it reminds me of a girl I knew once that would touch the back of my neck. They are that nice. "
So I guess Brimar it is...

 

The big thing in the case of the feedback-free 12AU7 based CJ preamps designs is to find tubes which don't go into oscillation. I'm guessing that this is probably why he only recommends exactly one tube for these units.

 

That's what I have gathered reading many threads on the subject, but from my own personal experience I have yet to come across this (knock on wood) with my tubes becoming microphonic or noisy.
Just why exactly does Conrad Johnson PV preamps have the bad reputation of driving the tubes hard, I have yet to get a clear answer. I would think the only way to push tubes hard and thus shorten their life is to bias them above their recommended voltage. If that's the case, one could just get a voltmeter and see if the Conrad Johnson preamps are putting out higher voltage than recommended for that particular tube at their respective pinout. I haven't actually tested my theory, but I am curious if the reputation of driving tubes hard is just a myth as Tonepub has indicated in an above post or if there is some other reason that is lost on me.

 

AFAIK, Pinnacle was only a re-brander, I'm pretty sure they weren't a tube factory. A Pinnacle tube could be UK, German, Japanese, etc...

 

They don't push their tubes overly hard. I ran a PV6 24/7/365 for more than 5 year on the same set of tubes before I decided to that they could use replacement.

There is just something slightly-off about their no-feedback designs which makes them extremely susceptible to oscillation. Their earlier feedback based designs were rock solid though. But its all that I can do to keep any of their no-feedback designs which I have tried from oscillating inside of my system.

 

I've been using some widely available and relatively low cost old stock Philips PCC88 tubes (not the later Yugo version) in my CJ 17LS2 preamp and they sound pretty good. I do have some others to try out, I know the Philips aren't the end game, but they also don't make me in any hurry to switch. The 17LS2 uses the four tubes in a "composite triode", basically just paralelled to keep output impedance low with only the one gain stage and no follower.