If you have a Steelhead-


I have been a very happy original owner of a Manley Steelhead for five years. All this time I had the stock tubes. I recently changed the tubes out to vintage 7044's which are just rectifiers in the Steelhead and then Matsushita / National PCC88 / 7DJ8's for the output tubes. I am posting because the upward. change in palpability and engagement is incredible. So if you happen to have a Steelhead... See my system if you care. My favored cartridge right now is a Lyra Etna Lambda on my hot-rodded Garrard 301 with Reed 3P on a Layers of Beauty plinth. 
128x128fsonicsmith
The nice thing about tube gear is just by changing tubes one can realize a sonic improvement! This is not possible with SS gear. 
Or living hell. But you can always go back to living heaven.
Any tube change will have different sonic outcome even same brand, same year, same week or day, same type.
Tubes are so.

G
Thanks to all, particularly EBM-so gracious!
I believe the Matsushita 7DJ8 is simply a nicer tube than those spec'd by Manley which were JAN Philips 6922's. Before buying a brand new ARC Ref 6 from a local AD I had an Audioprism Mantissa preamp for over 12 years and did a ton of tube rolling with it. In my experience the JAN is a polite solid 6922, an all-rounder and a good choice by Manley. In my system the 7DJ8 provides a bump up. Greater air, extension, and palpable grip. Not warmer per se but more meat on the bones.
Love your post! One has to remember manufacturers use tubes that will be reliable in the long term, not so much for sound quality. No owner of tube equipment wants early or unexpected tube failures but these can and do exist and if it’s under warranty, they want readily available tubes. 
Most tube equipment manufacturers encourage tube rolling but at the customers expense for good reason.

Have fun!