2. amps-preamps
  3. 189995-2556

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

I have an older Krell KAV amp that has been recapped and refreshed.  A technician that I respect very much said do NOT use a vacuum tube preamp with my KAV 250, or any other Krell amp for that matter.  Can someone with more technical knowledge than myself tell me why I should not be using a vacuum tube preamp with my Krell?  Are there some technical specs that I should be aware of when pairing?

Thanks

judsauce
judsauce OP
147 posts
 

@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!.

erik_squires
16,041 posts
 

OP:

Tube preamps use high quality film caps that usually have a life span longer than ours, but failures do happen and they may be small (few millivolts) to larger.

The input coupling caps on amps may vary depending on the quality of the amp. Lots of Yammies used bi-polar electrolitic. 40 years or so?

But worth getting into some details. The preamp coupling caps are rated for the voltage in the preamp, so 650V caps are not uncommon. Amp caps though may only be 50 V. Should the preamp cap fail and deliver 500V, it will absolutely break through the amp’s coupling cap and go boom. :)

If your preamp caps have just been replaced with high quality films they’ll last you a hundred years if they last you five. :)

The real guru on this subjecte though is going to be the manufacturer, @atmasphere who will correct me at length if I'm wrong.

invalid
1,180 posts
 

If you haven't bought a tube preamp yet, you could buy a transformer coupled tube preamp, then you would never have to worry about it. Most capacitor coupled tube preamps are fine with solid state amps. Again just remember to turn your system on in the correct sequence because the tube preamp has to stabilize before the amp is powered up.

judsauce OP
147 posts
 

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
1,872 posts
 

@erik_squires  , can you explain what happens that makes that "pop" when a preamp is inadvertantly turned off before the amp?

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