Tube flash

Jea, perhaps I didn't express myself well. I'd NEVER stick a tube like that back into my amp.

As Hifi mentioned: most testers do not apply full operating voltages(B+) to the tube being tested. Tubes, under actual operating conditions, will occasionally either short, draw high screen current or open a connection internally. In the event of a short or high current draw; your circuitry may suffer some consequences. The only way to minimize the odds of that occuring is to burn in the tubes at full voltage and cull the weak ones prior to their use, as is Upscale's practice with their power tubes, ie:(http://www.upscaleaudio.com/rare/tpm.htm).

Rodman, funny you should mention Upscale because that’s where these tubes were purchased. I guess it’s the luck of the draw, and in my case, my draw was aces over sevens.

And Newbee, you have an interesting premise. I should have mentioned though that my amps are the Premier 12 XS, which are configured to use EL34’s. So I assume the bias circuit is designed around EL34’s, but I’m going to ask Conrad Johnson that exact question. It’s also interesting that the last time I was at Conrad Johnson, I bumped into Lew Johnson and asked him what he though might be going on. His first question was what type of speakers are you using. When I told him Quads (63’s), he commented that they (Conrad Johnson) had some previous problems with customers that used Quads and their amps. He said that the Quads, under certain circumstances might draw too much current. This all sounded a little strange to me (I was always told Quads and tubes were a good match) but I’m not an electrical engineer and he was talking a little over my head, so I may have misunderstood. Since then I’ve taken the Quads out of service, and I’m using dynamic speakers. But the problem has continued.

Thanks again for everyone’s comments. Any other thoughts would be very much appreciated

Mr J- How old was the tube that failed? Have you contacted Kevin in regards to the tube's failure(and possible warranty)? Did the same thing happen more than once? You mentioned, "the problem has continued"(why I ask).

Jaffeassc, "so I assume...." You know what they say about what happens when you assume........:-)

Next time you talk to CJ ask them what the bias setting programed into the amp actually is. After they tell you ask them what the bias setting is in the 6550 model. Then find out if they actually checked the bias in your amps with your tubes in it as opposed to just noting the the tubes and the little LED were working.

BTW, some tube amp are designed to push their tubes very hard to meet high power spec's. Yours may just be one of those and underly the reason for CJ's statement about it having problems with a speaker that required more current, current their amp couldn't deliver.

BTW I drove Quad 63's with SED EL34 in a SFS 80 amp which only put out 40wts with this tube. I set the bias at 30ma and drove them off a 3.5ohm tap (internally configured). I never had a problem with tube reliability or tube life and I drove them hard enuf that they 'rattled' a tiny bit.

CJ's comments about the 63's could be accurate about their needs but I really don't under why a high quality mono amp couldn't drive them. As I recall they have a minimum impedance of about 3.5 ohms in the bass - any respectable tube amp should be able to handle that, especially a Quad which you can't drive that hard anyway. Since you have the same problem with dynamic speakers I suspect the CJ's may have a problem. If you have a techie nearby you might ask him to check and see what the bias actually is.

But, as I said in my first post I'm not a CJ authority.