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

Gs5556 10-29-2017
The heavy red ac wires enter the anodes and the cathodes are connected to pins 4 and 6 and then they’re jumped over to the second tube socket.

Re the comment I provided above in response to this statement, I just realized that the anodes and cathodes you are referring to are most likely the anodes and cathodes of the protection diodes, not the anodes and cathodes of the rectifier tubes.

If so, I am in agreement with your comment. But in any event the fact that the cathodes/outputs of the two rectifier tubes are connected together means that both tubes serve both channels. So both channels would continue to function (although probably in an unsafe manner) regardless of whether one rectifier tube is open or shorted or something in between, or even if one tube is removed.

Best regards,
-- Al

Al, the reason there are two rectifiers is so that they will hold up when the amp is at full power. At lower power levels one rectifier tube is sufficient.

IOW, the amp is be safe to operate (its been that way already) as long as the volume were not turned up (the loss of the filament load is already proven to not change the operating voltages significantly- other than the B+ is slightly lower right now). If high power demands are made, the remaining rectifier tube would eventually also fail.

Thanks Ralph!

Best regards,
-- Al
 

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)

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We've been using HEXFREDs for the last 25 years and they are in everything we make.

If they are really added into this amp as described, the tube rectifiers are really only there for show, since the voltage drops across the HEXFREDs is a fraction of that of the tube, so it isn't doing anything except glowing.