Vacuum Tube preamp with my KRELL KAV 250a, a no no......WHY?

Didn't the tech that told you not to do that tell you why?

I’ve been using a tube preamp for several years with my krell ksa 300s, it’s just as safe as using a solid state preamp. The reason this subject always comes up is because there was a certain BAT tube preamp that leaked DC and damaged amplifiers. Just make sure you turn your system on in the proper sequence, amp should be last to turn on and first to turn off 

I was told that vacuum tube equipment was "old 1940's technology." And that tubes created conditions and extraneous signals  that could/would fry certain components within the amp.  Is that so? 

I was told that vacuum tube equipment was "old 1940's technology." And that tubes created conditions and extraneous signals  that could/would fry certain components within the amp.  Is that so? 

I don't have the knowledge and understanding of electrical theory to comment on this from a technical perspective, but I would say that if you scroll through tyhe pages of this particular forum (amps and preamps) you will come across a ton of threads about, or icluding, people running tube preamps with ss amps.  I suppose there may be some, but off hand I cannot remember anyone posting about the combination damaging the amp.  But, as I typed, there may be some, but I think far and few between.  I cannot comment from my own experience because I have been running tubed preamps in front of tubed amps.  

The combination is often used and can be a magical. The tech is being overly cautious, but not entirely making things up.

Solid state preamps and tube preamps produce the same output voltages when working correctly. The issue with tube gear is that internal voltages are often 400V or greater. Most tube preamps use a "coupling capacitor" at the output to block that high DC voltage to nearly zero and let only the music go through.

The problem is on the rare occasion and over time the coupling caps can leak. If the amplifier lacks it’s own coupling cap on the input, or that coupling cap is not rated for the leaked voltage you can push the amp into overdrive, not to mention send your speaker cones ballistic.

Most solid state amps are "ac coupled." Meaning they use a cap on the input to prevent just such a problem. I believe I read somewhere that some Krell amps have an internal jumper in case you are not using a tube pre and want to avoid your music going through it. Worth checking on it.