Cary SLI-80 with one blown rectifier tube, BUT STILL WORKS just fine. How?

Thanks gang. Yes, Almarg has helped me with other tube-related mysteries before. Knock knock, Almarg?

I powered the amp down and removed the bad tube. It's getter flashing is "evaporated", and it looks like pictures I've seen of tubes that lose their vacuum or just go bad. Luckily I have a few backup 5U4 types around

My main question remains, though: In a Cary SLI-80 integrated, how can the amp seemingly work just fine with one of its two rectifier tubes blown? And, for that matter, can I run the amp with only one rectifier indefinitely (not that I would)?

I plan to contact Cary this week and see what they say.

BTW - The bad tube is (was) a Philips 5R4GYS from Uncle Kevin's shop. I purchased a matched pair from a fellow A'Goner a about a year ago. Sounded great, and the huge coke bottle style looks awesome. But nothing lasts forever. If an angel gets its wings every time a bell chimes, then what happens every time a vintage NOS tube goes bad? ;-)

Thanks again to those that chimed in.

Since I often come across old Audiogon forum posts while researching various questions on both A’Gon and Google, I thought I should close the loop on this one in case anyone else has this same rectifier question / issue with their Cary SLI-80 integrated amp and stumbles upon this post:

Here’s the explanation as to how my Cary SLI-80 was working just fine with one of its two rectifier tubes being blown:

I finally contacted Cary’s tech department, and spoke with Mark. Nice guy. I explained what had happened, that I just happened to notice one of the 2 rectifier tubes in my SLI-80 was blown, and yet the amp was working great, sounding great, and it may have been that way for several listening sessions. What gives?

Well, I – incorrectly – assumed that since the SLI-80 has 2 separate rectifier tubes, that one is for the left channel and the other for the right channel. I was wrong (that’s OK, I usually am. Just ask my wife ;-). Turns out, Cary runs the 2 rectifier tubes in parallel (and a shout-out to fellow A’Goners almarg and GS5556 who mentioned this possibility above). I’m not an electrical engineer, but I got the gist that – basically – the one remaining good tube was doing the work of 2, and that’s why the amp continued to perform just fine with one blown rectifier tube. Of course, that also meant the remaining tube was working harder, and if I had left it that way, it too likely would have blown prematurely.

I also – incorrectly – assumed that the HEXFRED upgrade that my amp has in its rectifier stage was “taking over” most of the work from the rectifier tubes themselves, and that may have explained why the amp was working just fine on one tube. Again, I was wrong. According to Cary, while the HEXFRED upgrade does “tighten up” and improve the rectification stage, the amp still relies on the rectifier tubes themselves to do the actual work, and the amp can still benefit from using higher quality rectifier tubes.

Cary also told me that part of their “ultimate upgrade” package for the SLI-80 is to completely remove the tubes from the rectification process and rely only on the HEXFREDs (and perhaps other magical circuits, I don’t know). This explains the pictures I’ve seen online of some SLI-80 amps with no rectifier tubes at all, and just small black metal covers over the rectifier tube sockets. So, if your SLI-80 amp – like mine – does have the HEXFRED upgrade, but also still uses rectifier tubes, rest assured you’re still running tube rectification, and can still benefit from rolling-in your favorite tubes (like the now ubiquitous Philips 5R4GYS, they just look so cool ;-).

I hope that helps anyone with similar SLI-80 rectification questions.

And with that, I rest my case, Your Honor.

 
From the sweet spot,

Mike (Mhwalker)