Ruby 6L6GCMSTR redplating

[Randall]

So I get a '65 Super Reverb in for a tune up. It's in great shape, all the right things have been done to it already. Customer brings in a box of new tubes, because he gets them free, says use whatever it needs. One of the mesa 6L6 tubes in it had a broken key pin, so I grab two of the matched quad Rubys and install. Bias them. Everything seems fine then while I'm test driving it, I hear an increasing hum and a smell, and then notice one of the Rubys is redplating. Put it back on the bench, and see that the bias on the offending tube is down to -12v. I pull the tube and bias goes up to -53v. Install another Ruby from the quad, and it runs at -53v.

Now did I get a new bad tube, and if so what could cause a tube to pull bias down like that? Not sure I've ever seen that. There's not much to a bias circuit, and this one seems OK to me.

[Leo_Gnardo]

Now did I get a new bad tube, and if so what could cause a tube to pull bias down like that?

Doubtless that's a bad tube. Gassy? Maybe in a few more days the insides will turn white.

[Randall]

I did swap sides and the problem followed. That one is going in the trash, not gonna risk anything.

[Chuck H]

Everyone here touts the Ruby tested and relabeled product. I haven't experienced the problem you've had, but...

I did have trouble with unacceptable microphony. Of three sets of Ruby tubes (all of which performed electronically and sounded better than JJ's BTW) only one was barely acceptable to use in the combo amp I needed them for. So there's that.?. As to the failed tube you encountered, I think anyone can throw a flyer now and then and I hadn't heard of that problem before with Ruby's. I haven't dealt with many personally though. All the Ruby power tubes I've purchased were mechanically unstable to some degree though.