With a bit of trepidation I have initiated correspondence with Western Electric regarding what will likely be diagnosed as a bad WE300B tube.  I bought the tubes from WE eight months ago and they have approximately 1,200 hours of use.

With the Western Electric 300B tubes installed in my Cary 300SEI amp, the amp’s “tube fuse” blows within 20 to 30 minutes after the amp is turned on, and it doesn’t matter whether the amp is idling or playing music. The tube fuse does not blow when using my Sophia Electric Classic 300B’s or with my stock Genalex Gold Lion  PX-300B tubes (which have now been sold).

The tube fuse is positioned in the 300SEI’s circuitry to protect the huge output transformers and a few pricey caps. Cary’s lead tech advised me that the tube fuse normally only blows when one of the 300B output tubes has failed or is on it’s way toward failure, and it does appear that one of my WE300B tubes is heading toward that end.

So, I am about to fill out the required RMA form and will probably be sending both WE300B tubes back to Western Electric for evaluation and analysis.  I did receive a very cordial written response from Western Electric this morning about the possible tube failure.

I’ll keep everyone posted on this WE warranty situation.  In the mean time, I will continue breaking in my Sophia Electric Classic 300B’s, which are turning out to be fantastic music makers!

For those wondering, the only speakers the WE300B’s have driven are a pair of 10 ohm Voxativ 1.6 full rangers that have an efficiency rating of 101db at 1 watt…..and, the tube bias has always been set between 70 and 72 mA. With 90% of the music I listen to being baroque, classical, and romantic chamber music, these tubes have been coasting down hill most of their lives, and they rarely, if ever, break a sweat.  

Disappointing that you need to avail yourself of the warranty, but very interested in your experience. Esp. since this is not an outright tube failure. Good luck.
 

Better than my luck with a pair of psvane.

They were a total loss with no warranty after failure.

I purchased a pair of Eml xls with a similar 5 year warranty

My guess is that fuse is there to protect the tube.  And the amp and not have your home burn down in a catastrophic failure.

In the MKV manual it says .250mA or .5mA for the rectifier tube fuse.

I would be 100% comfortable running a slightly higher spec especially if the tube manufacturer recommends it.

Thanks for the advice Groovy and CA.  I feel better about moving forward with the larger value fuse.  

The “tube fuse” on this amp actually protects the output transformers along with a few expensive caps.  The head Cary technician also told me that the tube fuse can sometimes save the 300B output tubes in the case of runaway bias current, but that is not it’s primary job.

Again, thanks for the feedback!

Doug

Steve and everyone else, I really mucked that one up! I posted from the Torii MKV Manual in a 300b thread. I used it as an example of fuse ratings being slightly flexible.

Also, confusing as I messed up writing fuse values.

From the Torii MKV Manual:

Quote:



Quote:

Awesome Doug! That's one reason you pay so much for these tubes. . . and a good reason.

CAJames, that was my first thought as well.  And after several hours of listening this evening, I wish I had my original pair back in the amp.  I wouldn’t say the new tubes sound unpleasant, but they’re no where near the sound of my well broken in ones.  

I told Mr. Whitener that I am curious why he sent a new pair of tubes, but haven’t received a reply yet.  My best guess is that one of my originals was dropped and broken.

Hey Doug, just curious if you ever got an answer on why the sent you new tubes instead of your old ones?

Thanks for the reminder, funch.

During the past 10 months I have had my Cary 300SEI sitting on the sidelines while the First Watt J2 that I bought late last spring has been breaking in.  The J2 has kept me very happy, but a few weeks ago I decided that I needed a little 300B magic so I swapped the Cary back into the system.  

(Side Note:  Since Western Electric replaced my beautiful sounding original pair of WE300B tubes in March 2023, the sound has never been as good as it had been with my original pair.  Interestingly, I never did find out why my original pair of tubes was not returned to me following their analysis.  My best guess is that one or both tubes were damaged while they were testing them.  Anyway, the replacement pair never sounded as good as my original pair--not even close.)

On Saturday morning, three weeks ago, I turned the system on and began playing music as I listened from other areas of the house while performing household duties.  In the early evening hours I went to the listening room for some concentrated listening.  The sound was good, but nothing like it had been before Western Electric replaced my original pair of tubes.  I had been listening for a couple of hours and suddenly noticed the right channel getting louder, so I opened my eyes, looked at my amp, and saw the right channel 300B tube red plating.  I jumped up, ran to the amp, and powered it off.  

Upon examination, the tube looked fine, but not knowing the consequences of the red plating incident, I contacted Western Electric to seek advice.  They asked me to return both tubes for evaluation.  Yesterday I received an email from Western Electric stating that the questionable tube "showed a fully depleted getter flash, indicating a gassy tube."  They went on to explain that the gassy tube was likely caused by rough handling during shipping.  I was happily surprised to learn that the tube has been defective all along. Western Electric is sending a new tube matching the specs of the other good tube.  I've got my fingers crossed, hoping that I'll again get the beautiful sound of my original pair of WE300B tubes.

Update on my Western Electric tube situation:

I received a replacement for the defective tube that was determined to be "gassy".  After several days of break-in I'm ready to say that the sound quality is equal to that of a the original pair that I purchased two years ago.
These Western Electric 300B tubes, complemented by three Cryotone 6SN7's in my Cary 300SEI, produce incredibly beautiful music, and we're still very early in the break-in process.  

You can't beat a five year tube warranty!