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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
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.
dusty
60 posts
 
Arizona Hi-Fi is an ARC dealer. You might want to take the tube (and the amp) down to them to check the tube(s) and verify that the bias resistor is okay. If you're lucky, all that will be needed is a new tube. Also, having the dealer check ALL the tubes will verify that they are new tubes.
Don't laugh, I have replaced tubes in my used tube amp purchases with fresh tubes purchased by me. The tubes that came with the amps didn't see duty until I checked their condition. Some of them were on their last legs.
rugby1
27 posts
 
I had the vs 110 and the manual states to use 65m v but that was with the older 6550 not the 6550c that the new ones had for info .
jjb67 OP
3 posts
 
I checked the resistor with a multimeter- fortunately it's OK- just waiting on a pair of tubes. Thanks for the Arizona Hi-Fi tip!
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