[phyrefly]

I've run it for more than 100hrs now, so I'm guessing they're burned in.

In the past few days, one of the channels have developed a very annoying hiss. If I switch the driver tubes, the hiss goes to the other channel, which leads me to suspect that the driver tube is dying (stock Chinese tube).

It's funny - since tapping the tube lightly temporarily stops the hiss!

Also, both driver tubes seem microphonic when I tap them - this doesn't happen with the power tubes.

Any ideas what might be wrong?

edit: Just did a visual inspection of the innards and everything looked fine.

 

[breakfastchef]

Quote:

Originally Posted by phyrefly /img/forum/go_quote.gif I've run it for more than 100hrs now, so I'm guessing they're burned in. In the past few days, one of the channels have developed a very annoying hiss. If I switch the driver tubes, the hiss goes to the other channel, which leads me to suspect that the driver tube is dying (stock Chinese tube). It's funny - since tapping the tube lightly temporarily stops the hiss! Also, both driver tubes seem microphonic when I tap them - this doesn't happen with the power tubes. Any ideas what might be wrong?

Your troubleshooting ideas were good. If the problem follows the tube, chances are the tube may be going bad. Contact David at Little-Tube. He is quick to respond to problems and will surely take care of you. Make sure you tell him that tapping the suspected bad tube temporarily stops the hiss.

If you turn the volume down on the MKII, keep the headphones on and turn the unit off, you may hear a tinkling sound. It is really cool. Those are the driver tubes cooling down. Yes, if you hear microphonics, it would be from the driver tubes, not the power tube. I never had a microphonics problem with my MKII.

 

[phyrefly]

It was bought directly from sword_yang in China, so I'm guessing sending it back for warranty would be very expensive.

Does the microphonics indicate that the driver tubes are leaking/dying?