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

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.

Actually, OP, after reading @erik_squires  reply, I do now remember someone posting about losing a pair of speakers due to what @americanradiance just described.  That must be what your tech was talking about.

Typically you want the input impedance of your amp to be more than 10 times the output impedance of the preamp for optimal performance.  The input impedance of your amp is 10 kOhms so as long as the preamp is below 1k Ohms (as many are) it should be fine unless your amp is different from almost any other solid state amp.  I’d shoot Krell a call just to make sure, but I highly doubt it’d be a problem to use a tube preamp.  As mentioned above, many people here use a tube pre with a solid state amp with no problem and wonderful results.