EH "quality" strikes again?

[JD]

I agree with alot of these posts. The JJ, =C= SED, and Mullard reissue are excellent sounding and for the most part very reliable current production EL-34s.

[KennedyBlvd]

It's craziness! I would love to know how this physically happens. As in, what is going on in the tube to drift so much?

What's going on is that a reputable seller will burn their tubes in under extreme conditions before selling them. Sellers who don't care... won't. I'd just cathode-bias one of those old Music Man amps, I'd use cathode bias so I could burn the tubes in without worrying about bias. The Music Man has around 735 volts on the plates. For a test chamber I'd mod the thing so the grids run just over spec for voltage, then I'd burn 'em in with signal applied running into a dummy load overnight. Surviving tubes would be matched and shipped, DOAs go in the shitcan. That's the RIGHT way to do it!

Mil-spec gear also gets a couple hours on a vibration table, anything that doesn't shake apart is good, anything that shakes apart goes back for re-work, then it gets a shake down again. Ever wonder where the term "shake down" came from?

Don't have a vibration table? Whack your test amp with a deadblow hammer every so often.

BTW the poor man's way to identify a shorted tube... without a tube tester... is to pull ALL of the output tubes. Then stick 'em back in one at a time, for this test you never want to have more than ONE output tube in there at once. Speaker load should remain connected. What will happen is that when you insert the shorted tube, and it's usually only one in a quartet... the fuse will pop. That's how you figure out which tube is bad at a gig when you need to make it through the set. Just know which tubes are opposing pairs, pull the shorted tube and one on the other side, you can re-set the impedance selector if you're picky and run the amp on two output tubes to finish the gig. The high voltage will probably rise due to the reduced load and the bias may be incorrect but a healthy 100 watter will happily finish a gig as a "50 watter"!

[Country Boy Shane]

Just got my quad of EL34-EH and they went poof on me. I had a quad of Winged C's in the amp, put in the EL34EH's, biased it up to 17w of static dissipation, let it burn for a while, and rebiased. Plugged in my guitar and it sounded fine at lower volume... as soon as I turned the volume up, the amp lost all sound and popped the HT fuse. I replaced the fuse and put the Winged C's back in, rebiased, and the amp worked fine for 10 minutes of CRANKED playing.

You got hosed...

Stick to Svetlana's and JJ's my man.