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 tried calling Krell close to where I am, they're in Connecticut. But when I went to leave a message with tech support I got a nice sounding man who said, "please leave me a message". Then his mailbox promptly told me, "voice mail box full". So, I left a message with sales. 50 bucks says I'll never hear back. Not like the old days, for sure. Wife runs the company now, Dan is off selling, well, you know what. 

@immatthewj 

@invalid 

Thank you both!

@erik_squires 

When you say "over time, the coupling capacitors can leak", what if they were replaced during the reconditioning? And, what would you consider a time frame for malfunction: 50 hours, 150, 250, or over depending on use?

Thanks again, everyone!.

@immatthewj   you're too funny. Nothing to get off the pot on. Check my virtual system. It's the preamp that I have that's in question.  It has the best music coming out of my system that I have ever heard. That's why I'm scratching my head.

@lynn_olson  thanks so much for that information. It was very detailed and much appreciated. A big wealth of knowledge that I hope others studied as well.

@lynn_olson   Your input is much appreciated.

HERE IS THE SKINNY:

I have 2 KAV250a's. In May, 2022, I had the oldest one recapped with some new resistors, etc, to the tune of $1,600.

Being a guitar player with several tube amps, I always loved the warmth and body vaccum tubes offered. 

In March of 2023 I bought the Audio GD Vacuum HE1-XLR BALANCED LINE PREAMP.  I used that along with my OPPO BD-95 for cd, and my Sonic Frontiers SFP1 phono pre-amp.  The phono preamp was recapped and reconditioned by Glenn at Parts Connection.  Those sources, along with the pre-amp and amp have logged over 220 hours in my diary with absolutely no issues.  The sound, to me, was fabulous. 

Fast forward to this past week.

THESE ARE THE EXACT CONDITIONS IN PLACE WHEN I HAD A MALFUNCTION:  I had just purchased and installed a pair of NOS Mullards and a pair of Gold Lions in the Sonic Frontiers phono pre-amp.  I fired everything up and put on Dire Straits lp, Leaving Elvis.  Before the song was over, the left channel went silent.  Then about a minute later, followed by a mild and dull low volume "thud", the right channel went out.  No smoke, no smell, just no music.  My trouble shooting revealed that the amp was not working.  So, I swapped in my second KAV250a, immediately put back in place my original tubes in the phono pre-amp, and have only played the OPPO blue ray so far.  And everything is fine.

The Krell has 26.4dB of gain, input sensitivity of 2.15 Vrms, and 100K ohms input impedance.  

The Audio GD Vacuum HE1 XLR LINESTAGE PREAMP has an excellent review by STEREOPHILE, whose link I will attemp to paste below.  I bought it from Walter and Underwood Hi-Fi (whom will be retiring this week, he sold the company.)

The amp is going back to the technician next week.  So, is this a bad combo, in your opinion?  By the way, the malfunction could be independent from the tube swap in the phono preamp, and it could be coincidental.  

All opinions welcomed.  Have a great Holiday Weekend, and pray for our soldiers.

Jud

@mattw73 Thanks for your reminder about the sequence of powering on and off.

I have to admit, I sometimes forget and then end up crossing my fingers.  Not good.

Regarding the power going out or flickering during storms: I have both preamp and amp going straight into fresh/new sockets in the wall.  Whenever there is even the slightest prediction of a storm, I yank the power cables on both until the threat passes.  And if I'm away for a long time, I pull them just as a precaution.  

Like you, I also prefer some tubes in the chain.  The Krell paired with a SS preamp sounds a bit bright for my taste.  And there is nothing like high volume creamy distortion when driving a class D tube guitar amp. Buttery smooth and so fun to play.  But a vacuum preamp, for my taste, rounds out the brittle high end and adds a bit of warmth.

@atmasphere  Thank you so MUCH for taking the time to reply.  I do feel a bit better.  My reply this morning on this thread at 8:16 A.M. lays out my problem that prompted this thread in the first place.  Something did happen to my KAV250a.  But there was no smoke, no smell, just a soft malfunction-left channel first, right channel second.  I'm taking the amp back to where it was re-capped and refreshed in 2022, so next week I'll have more idea about what caused it.  Might not have been the pre-amp at all.  But, thanks again for your input.

regards,

judsauce