2. amps-preamps
  3. 1286686656

tube amp help

I recently purchased my first tube amp- a used Audio Research VS 110 with new matched SED winged C 6550Cs put in by the seller. They were biased at 55mV per his recommendations. I've been listening for 1 week- it sounded great until today. When listening there was a brief pop sound and a quick spark from tube 7. I turned it off, waited a couple hours...turned it back on, they all glowed orange, I checked the bias. tube 7 had 0 mV, all others 53-55. Is the tube blown? Do I need just need to reset the bias? If I need to replace the tube do I need to replace a pair?? Any help would be appreciated - I am a tube amp newbie.
jjb67
tubeo
72 posts
 
Make sure that the Amp is connected to your Speakers when setting the Bias and as stated above give the Tubes a warm-up first.
jjb67 OP
3 posts
 
Thanks for your responses. I appreciate the reference to Antique Electronic Supply in AZ since I live in Scottsdale. The Audio Research manual does say 65 mV DC- but the seller said he was told 55mV from his tube supplier for these particular tubes. I might change it to 65. The tubes are matched pairs- so I guess I'll get a new pair.
jjb67 OP
3 posts
 
In the mean time- I assume I shouldn't use it, but someone told me I could listen at low volumes with a single blown tube.
lostbears's avatar
lostbears
538 posts
 

I run SED winged "C" tubes in my Ref 110. That is the 6550 tube that Audio Research recommends for all their amps. These tubes don't need to be run at that low a bias. And a bias that low will adversely affect the sound quality of the amp. I run the tubes in my Ref 110 at 63mvDC.
newbee
4,767 posts
 
FWIW, I don't know about the VS110 but a lot of ARC amps will take out a resistor in the bias circuit when a tube shorts out (as yours did). That resistor acts as a fuse so to speak. Don't be surprised if you find when you replace the tube that it won't bias. If that occurs you best have a techie (or ARC) replace the resistor.
More to discover