Preamp tubes in power amps

Thanks!  I’ve dealt with Kevin at Upscale.  They sold me a bunch of 7DJ8s that they promised were fine substitutes for 6922s but my BAT destroyed them, and Victor at BAT said he had no idea why someone would represent 7DJ8s as suitable.  I know the voltage is close.  But the BAT does not have a reputation as a tube destroyer,

what I’m asking is where would upgraded preamp tubes have the most impact?

Thanks again.  Yes I did tell Upscale about the issue.  They tested all the tubes and sent the survivors back to me, but I haven’t used them as the only 6922 sockets I have are in the BAT.  I can’t put them back in there.

The only gripe I have about Upscale was his statement about 7DJ8s being a perfect substitute ...”trust Uncle Kevie on this one.” Not “make sure this is ok with your gear.”

Oddly, Victor at BAT seemed skeptical that changing tubes would have much impact.  

Thank you. This is helpful advice.

Upscale didn’t know. I don’t think they should be quite so certain in their marketing materials that 7DJ8s work anywhere.  But I couldn’t say that there was anything specifically said to me, or omitted, that was a problem with Upscale. I ordered several sets and had ruined most before Kevin could respond. The tubes DID sound good...

The issue was years ago, and so I’m not going to pursue it with them now. It comes up mainly because at that time I decided not to try NOS tubes in this preamp again. But now that I have it available to my best amp/speaker combo again, I am again wondering if some NOS would add magic.

Thanks everyone for their feedback.

Regarding the above comments, I suspect that their concern about the VK-3i actually came from my experience.  That happened nearly 10 years ago and so I assume that Upscale Audio has updated their information regarding the BAT preamp because of my tube losses. I think I have those EH tubes in my preamp now - so it's interesting to note that AFTER I had issues they issue advice to avoid my pain.

That said, it also looks like, based on the Audioshark forum, that another user of the VK-3i has also discovered that it is a bit more sensitive with tubes than other preamps.

So, must consider what to do here.  I did like the sound of the National 7DJ8s and the Philips 7DJ8s before they were ruined -  a little mellower on the top -- but I would also not be happy to find out that my VK-3i destroya $500 worth of NOS 6922s...