Spikes on right channel, please help

[Gauss]

I have more than 5 months with my Crack built with speedball. It has been a wonderful experience so far!

Now I'm having a problem, today my right channel started to give some kind of spikes, the driver could be heard as it were to blow up, the spike could be heard from intervals of some seconds so I immediately disconnected my beloved HD600 cans and shut off the amp. Since I use my Crack at work I'm expecting to take it tomorrow to home to give it a check.

What would be the most likely to be the problem? Some part from the speedball could be failing? I think I'll first do the check of all voltages as I did when I built it. I could also use my voltmeter to watch the right channel but should I have something connected to the right channel, maybe a resistor? Maybe also I'll watch for some sort of "almost-shortcircuit" and give it a touch to all solder joints.

By the way, I've already tested my phones on my weaker portable amp and no spikes, anyway I'll take my phones to home to also do some tests, the shame maybe would be that I don't have another poweful amp to give a thorough test to the phones. Also the music I was listening don't have spikes.

I would really appreciate help to look for the problem, thank you!

[Doc B.]

Are the spikes random, or are they in a rhythm? The rhythmic deet-dah-deet-dah-deet kind of buzzy beep is cell phone. A more random popping or loud static sound could be a tube going bad or a bad connection somewhere.

[Gauss]

It's a random spike. I did a last test and I regret it, won't do it again until the amp is well checked.
A song played fine almost to the end when the right driver heard as blowing up and went muted, I disconnected the phones from the Crack and tested them on my portable amp, the phones are right and working.

[Gauss]

As you said Doc, a failing tube. I replaced the Electro Harmonix ECC82 by a Tung Sol 12AU7. The problem is gone! The best of all is that the Crack is sounding more powerful and with more authority the bass is better now. This is the first tube that arrives since I stop by at ebay because of the former problem. More tubes coming! Time to start rolling lol.

Any way I'm a little concerned about a failing tube, isn't it a way to prevent the headphone from being damaged while a problem like this one starts happening? Any modification to the Crack? Would it be worth it?

Thank you Doc!