Is there a strategy in preamp tube placement?

@xcool 

The noise testing service is somewhere on the Brent Jessee site, $10/pair I think. You have to request it in your email to him.

With 6SN7s from the 40's or 50s, I always order noise testing. In Brent's description he may say a certain tube is low-noise, then it's not necessary to pay an extra fee. As @mulveling stated, later generations of tubes used different internal designs to mitigate microphonics. Some military-grade tubes are "ruggedized" with extra support rods and micas to withstand shock and vibration. With 6SN7s, there's a chance these tubes may be less microphonic.

Thanks @lowrider57 for the information on the fee.

I'm still fairly new in tube rolling, and learning a lot from this thread.  Thanks!

These days I’d also be leery of counterfeits of tubes that are now 70 and more years old. The best sounding KRs are the black glass variant. You can’t see what you’re buying.

     YEP (Brent charges $5/tube for noise testing)!

     A vid, describing his testing method, can be found just into the the tube description portion of this page:                       

                     http://www.audiotubes.com/6sn7.htm

"These days I’d also be leery of counterfeits of tubes that are now 70 and more years old.

The best sounding KRs are the black glass variant. You can’t see what you’re buying."

     The 1940s, Ken-Rad, VT-231/JAN-CKR/6SN7GT has bottom gettering, a very unique top mica and support structure, including copper posts*, which are plainly visible (blacked glass or not).

     I’ve never seen a counterfeit CKR proffered, though: I’m certain I’ve not seen everything for sale out there.

        On the page linked previously; Brent has a three part vid, on spotting genuine NOS tubes, worth viewing by any seeker.

   *ie: https://www.ebay.com/itm/185479311423?hash=item2b2f6db03f:g:6~QAAOSwGRliuJhB