Is there a strategy in preamp tube placement?

re: " The Full Music seems reasonably priced, might have to experiment."

To @coachpoconnor, I went with them long before the Linlai came out, and was tired of chasing quality matched pairs and quads of vintage 6SN7s any more. A SET/Triode obsessed gear friend of mine turned me on to them a few years back. Its worth following the other 6SN7 thread on Agon for more info. I would not say they are better than Linlai, yet I do like the TJFM better in some ways then the psvane CV181-MKIIs, and vice versa in other ways. Different sounding tubes, comparing them to each other.

That’s where I started mixing them within the SLP-98 for an enhanced result. Like mixing in a little butter and lemon for a good pasta dish, hahaha. :)

If you have Linlai now, will be interested in your feedback if you mix them with psvane or TJFM later on. I started doing this to have at least 2-3 other type quad sets in reserve while I mainly keep my vintage stuff tucked away and rotate them in every once in a while. Honestly, no need for it after I got the TJFMs in rotation, and they fit and seat down very well in the 98. PM if interested, I get them from their largest distributor overseas, with fewer middle-men and handoffs in shipping, helps reduce shipping damage some, and this dist packs them well layered in cotton, good boxing. Cheap insurance actually.

They learned this years back after a series of tubes failing after poor packing/shipping. Mine have 2yrs run-in on them now. So far, like mixing psvane/tjfm. Having another quad of Linlai will be good. Thx

With KenRad, I've had problems with microphonics that were not totally curable, even in my Atma-sphere MP1 where the tubes are entirely enclosed in the chassis and my MP1 is 22 feet away from my speakers with a couch in between.  However, the problem was "tolerable".  Then I switched to RCA VT231 gray glass in the gain stage.  They're not quite as terrific as the KR but less microphonic, at least the pair I've got.  Much better in that regard. In my Atma amplifiers which sit next to the speakers, I use 12SN7s or 12SX7s (6SN7 with 12V filament); for some reason these are not microphonic at all.

Questions to you guys with the Ken Rad with microphonic. How do you guys deal with this issue? or do you simply just live with it? Thanks.

Yes, I can confirm Ken-Rads tend to be the most microphonic and can have come-and-go noise issues. Vibration control tweaks, tube dampers - these have no effect on such a problematic tube. The only "solution" with such a tube is to move it further downstream. The more upstream it’s positioned, the more gain it has stacked after it, amplifying all that noise crap (or in the case of microphonics, making a stronger feedback loop!). Having high sensitivity speakers acts like extra downstream gain, and exacerbates the issue. The only exception is a tube right before a volume control, which acts like a large negative gain in most systems, but it’s rare to find a slot like that (maybe cathode follower output in a tube phono stage).

With Ken-Rads, I’m only consistently able to use them in power amps. Almost never in preamps, no matter the slot. And DEFINITELY not gain slots in the preamp. A preamp slot in an integrated amp doesn’t count as an "amp slot".

@xcool

I own two pairs of Ken Rad VT-231 black glass and a pair of clear glass (1945). When purchasing these tubes or others from the 40’s, it’s imperative that the dealer offers testing for noise and microphonics. Andy from VTS, Kevin Deal, Brent Jessee (for a fee) all noise-test their tubes. But there’s no way to tell if a tube will become microphonic at some point in its lifetime. All three pairs of my KR’s have remained noise free. But one of my beloved Tung-Sol BGRP’s went microphonic after 3 years. I've been using these tubes in gain stages of my preamp and amp.

There are many causes of noise from a vacuum tube and microphonics is only one of them. You can test for the other kinds prior to purchase but it is hard to predict whether a tube will be microphonic or not in your home system, because circuitry, cabinet damping and/or direct tube damping, proximity to speakers, typical listening levels in terms of SPLs, socket design, etc, all contribute to the problem or to its prevention.  That said, some tube types are just more prone to the problem than others. In the case of octal base triodes, like the 6SN7, 6SL7, etc, those are just more likely to be microphonic.  Some say this is due to the relatively large size of the glass envelope and the fact that the plate structures are more or less prone to vibrate in the large volume environment.