1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

[CTN]

So I was taking a break a little while ago from all the math and physics studying, and decided to play some guitar.

Cranked my amp up and was doing some tweaking for some real high gain marshally sorta tones with a nice low mid grind. It was groovin, goin really well. And then suddenly, one of my EL84 power tubes starts red-plating and the lead channel gets predictably thin and loses volume.

I checked the tube indicators on my H&K Tubemeister, and one was flashing (means it's over-current, that's the one that was redplating), and the other indicator was on constantly (means it was under-current, but otherwise ok). Together that means I should replace the redplating tube, but the other one is fine, according to the H&K Tube Safety Control system.

In any case, I shut down the whole amp and let it cool for a bit. Then I turned it back on, and checked the TSC again. This time, it showed no problems and correct biasing. So I turned it up again, switched to the lead channel and proceeded to rock out again. It's behaving like nothing ever happened. No loss of tone, volume, gain, or anything.

What gives?


On a side note, I got these tubes (TungSol EL84s) as a matched set from theTubestore.com, and they're extremely reliable. I have no doubt that I did get a matched set from them, but I checked the matching with the TSC system and it's telling me that they're WAAAAAAAAY mismatched (well matched set is indicated by less than 4 blinks of the indicators. I got 10). I mean I know tubes drift over time but I seriously doubt that they could've drifted from being a matched set to being pretty much completely mismatched beyond all reasonable tolerances. Again, what gives?

 

[JeffB]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

Thats what happens when one tube is going bad. Had the same thing happen with the original VAs, and some JJs. Soon after the bad tube fried, and on my JJ tube fried, AND blew a fuse. The amp is trying to compensate by running cool, but its just a matter of time.

 

[Gearjoneser]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

The amp is trying to compensate by running cool, but its just a matter of time.

Yep. Throw away the bad tube, and keep the good one as a spare. Put a new set of JJ EL-84's in it.

I have to admit, one of my favorite features on new amps is biasing circuits, and/or bias knobs and points on the back panel.

 

[MetalManiac]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

I can help you. PM me, I'll give you my Paypal, and for 10 dollars I'll tell you...nah, ur a good ol' boy..I'll tell you for free. Its not a bad tube. Run the good tube in the socket that redplates and i'm gonna bet you it redplates also. Some bad resistor, or cold solder joint.
You could also ask Ratherdashing. He's got a Masters degree in E.E., plus , he knows everything, even the meaning of life.

 

[CTN]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

Thanks guys. Guess I'm gonna change em out before it becomes a bigger problem. Good thing I have spares. While I do that, I think I'll also check the boards to make sure no components are on their way out as well.

Yep. Throw away the bad tube, and keep the good one as a spare. Put a new set of JJ EL-84's in it.

I have to admit, one of my favorite features on new amps is biasing circuits, and/or bias knobs and points on the back panel.

Why JJ's specifically?

I kinda wanna try those TAD EL84 STRs that are supposed to sound more like 6V6s. or a pair of Mullard reissue EL84s.

 

[JeffB]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

Not to speak for Joe,but the JJ sound good, are consistent, reliable, and are priced well, is my guess. I do believe the TM series are a.bit rough on tubes. I still have an original JJ EL84 from 4 years ago when I bought my Class5 and it has had gazillions of hours put on it (including being left on overnight several times). Still sounds great.

That said, I really like the Mullard RIs, they are smoother when they break up(but still get strident like any el84 pushed too hard), and a bit more balanced EQ wise than the JJs. Keep in mind the Mullard Ris have little headroom though.

 

[misterwhizzy]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

I've tried a set of Chinese unbranded, a set of JJs, and a set of Mullard RIs. I prefer the Mullards a little bit over the JJs. They're a hair smoother, but they just sound a little less harsh through the whole spectrum. Are they worth 50% more? I don't think so.

 

[CTN]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

I stuck a set of chinese Shuguang EL84s in. They suck. Everything got a lot more mushy/fizzy/buzzy and undefined.

I has a sad.

 

[alteredbeast]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

balls. still under warranty if some of the innards are peacin' out?

 

[CTN]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

I checked earlier, innards are fine. Must've just been the tube peacin' out. I noticed some scorch/heat-stress marks on the glass right by the plate vents inside the tube that was redplating. The other one was fine.

 

[JeffB]

Re: 1) Rock Out. 2) Tube Redplates, shut down rig. 3) Back to normal. WTF?

I, surprisingly, have had great luck with Shugang B 12ax7 in both the TM and my C5, but the Valveart/Shugang el84s definitely leave something to be desired. I got my Mullards on sale from Tube Depot, Whizzy has a point, though we are talking only 10 bucks or so for a pair,difference. In my Class5 which is much more sensitive to tube changes in every position, the Mullard is def worth the extra $ for me.

If you have the master wound up on 18w mode much of the time, the Mullards will probably be worth a try.