Cartridge mistracking just killed a pair of 12AX7's in my amp - is that possible?

Playing a Ben Webster Plays Ballads LP, I heard the stylus skip and mistrack twice in a row on some loud passage, accompanied with a pretty loud noise.

After inspecting and cleaning the vinyl with a carbon brush and the stylus with ZeroDust, I've replaced the stylus on the vinyl and continued to play the LP. Afterwards, while playing normally, I have noticed a slight variation up and down in volume, and finally it settled, but at a noticeable decrease in volume.

Looking for the source of the trouble, I discovered that the two 12AX7's on my PrimaLuna Four went dark. The quad EL-34's and the pair of 12AU7's still work fine.

I wonder if it is even possible for a burst of loud noise to just pop two new production vacuum tubes with low hours on them like that?

Any experience and wisdom to share here?

 

Are you sure it was a mis-tracking you heard and not the tubes crapping out?

 

One time I sold a pair of speakers to a guy and he claimed that they blew his phono cartridge.

I think it's hugely unlikely that a record skip could cause damage to the electronics.

 

There definitely was a double-skip, and a bad noise almost simultaneously, which I now presume was the tubes crapping out. I'm just not sure if it's a close coincidence, or a cause-and-effect.

 

Well, he certainly was wrong - I don't think signal travels back from speakers to cartridge. However, if he had his turntable and speakers on the same surface, and the turntable wasn't isolated, then the resonance from the woofers might have been transferred to the tonearm, thereby damaging the cart. That still would be his fault, not yours, or the speakers'.

 

If any part of a tube amp would be injured from a skip, it would be the output tubes. The input tubes should be impervious to some pretty extreme signals in my experience.

Also, the tubes going out means that the tube heaters must have stopped lighting-up. Heater loads are completely independent to the signal which is being fed to an input tube. So if there is a correlation here, then it must be that the tube blowing managed to (acoustically) cause your record to skip.

Pull your tubes out and check the resistance of their heaters with a multimeter. I'm guessing that the tubes are just fine, but that the heater supply inside of the amp failed.

 

Not a cause and effect thing at all. The skipping earlier was just a coincidence. The amp must have a failure in it somewhere. The tubes themselves are probably fine.
-Bill

 

The amp kept on playing even with the 12AX7's darkened and with only the 12AU7's aglow, just at a slightly lower volume.

I then turned the amp off for a while, took out the "failed" tubes, and replaced them with an old pair of Pro-Ject 12AX7 tubes taken out of my Tube Box S phono when one of them became noisy.

The "new" tubes light up perfectly, play without an issue, and are very quiet (unlike when they were in the Tube Box S). There was a momentary loss of volume that had me baffled and concerned a bit, but the volume came back up immediately and had played through a full LP last night. It was around midnight, so I wasn't at liberty to continue experimenting, as I live in a tenement building and have pity on my neighbors.

Tonight I will do some more playing and see how the amp and the tubes behave. If it's the amp failing - I'm not too happy. I expect a PrimaLuna product to last a lot longer, especially with the light use it has seen from me. Not too excited about having to ship the amp for warranty repairs, either. But I will wait and see if it becomes necessary. Keeping my fingers crossed in the meantime.

 

What brand of the 12AX7s do you say darkened? If these were something like Sovtek LPS, then you need to realize that these 12AX7s are always dark. And the rest of your symptoms don't make any sense if your 12AX7s were not working. Because if your 12AX7s were truly out, then there should have been no sound at all.

 

Those were stock PrimaLuna, and they would always be aglow, until last night. Their replacement light up just fine.

I will have the problem tubes checked, at least out of curiosity.

 

nope, not possible
purely a coincidence
small signal tubes should not be too "bright" anyway (they generally aren't by nature)
if they're glowing like power tubes then something is amiss
Michael

 

Something sounds very wrong with your story here... I'm not sure of exactly what it is yet, but none of this makes sense. If your tubes were lighting, and they aren't now, then there should be no sound.

 

PrimaLuna doesn't make any tubes - they just brand them - I don't know who their OES vendor is - probably several
I have read a number of complaints regarding whatever it is that they do use
So much so that they felt compelled to put a little spin on it
Tube Issues — PrimaLuna USA
You'll be OK - tubes are one of those things where it is true - they don't make 'em like they used to
Michael

 

There are 4 input tubes: 2 x 12AX7 and 2 x 12AU7. Only the two 12AX7's went dark, and the volume became lower, but did not disappear. I guess the 12AU7's can also pull some weight. With new 12AX7's in, now all four input tubes light up and the sound is back to normal level, with the exception of one brief period.

In fact, I'm going to play it some more now, just to make sure everything is OK.

 

When a power tube on my PL5 started going out I was sure it was my turntable. Sounded just like record popping. Maybe that’s what you heard.

 

Yes, sounds very much so. It was two loud pops, which I presume was one for each of the two tubes.

So, perhaps it was the two pops that caused my stylus to skip, and not the other way around. The LP played was brand new out of shrink wrap, and played flawlessly on second try.

 

Right now, as we speak, the amp is playing perfectly, all tubes are aglow, no issues with sound or volume. One thing I'd noticed: right now my power conditioner is showing 122 Volt. Last night, when this thing happened, the voltage was only 108 - could this voltage drop have somehow contributed to the tubes' popping? Just thinking out loud.

 

Everybody with guesses forgot to ask the OP what caused the double skip. Did it just make a double skip while playing a record or was the skips due to the turntable being bumped while playing a record? Or a neneedle drop accident? When brushing your stylus to clean it without lowering your amps volume control, there is often a scary sound which sounds like it has some definite low frequency component to it. Like a dropped or severely skidding cartridge. Low frequency component would be the most likely frequency to cause problems, but do not know if that could be severe enough to damage tubes.

 

It happened mid-song. I think I have the answer already. Read above.

 

Three LP's in a row played without a hiccup. Amp is behaving admirably. I now believe it was the tubes' simultaneous popping that caused the skip. I wonder what makes two input tubes to crap out at once. Otherwise I believe the issue is solved.

 

Not "bright" like power tubes, of course, but still visibly aglow. From day one, it gave me pleasure to see two rows of tubes lit up when the amp was on: four EL-34's in the back, and four small signal tubes at the front. So, when two out of four in the front row go dark, it's very obvious - it's like two front teeth missing.

 

I'd guess they may use some Chinese factories, and maybe JJ. Granted, none of those are the epitome of tube quality of yesteryear. The good part is, new production tubes are sanely priced, for the most part.

 

Agreed. We're kind of wired to always be looking for connections even when there aren't any.

I remember as a teen working in a PC shop where the tech double-clicked on an icon on a lady's desktop and the hard drive died immediately afterward. She was understandably upset, yet we could not make her understand that action had nothing to do with a part dying then.

At work, I have to tell users lines such as "It's like getting a flat tire the moment you switched radio stations." so they can better understand how entirely unrelated the action is with the symptom they're having.

 

sidetrack a bit.. but even thou that's not your fault and sounds like the guy is another George Mcfly high school pushover?

Glad the system is good now.

 

Not possible to have a cartridge issue ruin 12AX7 tubes.