[Deterministic]

After lurking for a few weeks I decided to pick up a DarkVoice 336SE as generally people seemed to be having good results and the tube rolling options were fairly wide.
 
I received the amp today, and unfortunately it seems to be broken =(
 
I tried many sources in vain to no avail, I did however notice that the stock 6N8P driver tube didn't look so great, and also didn't glow at all upon powering the amp.
 
I searched around Head-Fi and could only find one other instance of someone receiveing a DV with a bad tube, so it seemed very odd.
 
The stock 6N8P driver tube makes a noise like the broken filament in a lightbulb in the base when I roll it around in my hand, a faint rattling noise that is fairly disconcerting.
 
The power tube lights up quite brightly when the amp is powered on, but the 6N8P has no visible light at all, even after 20+ minutes of power.
 
I have already ordered a replacement 6SN7 tube, my questions are as follows since I am brand new to tube amps, and I want to be sure I'm on the right troubleshooting path.
 
1. Do 'most' 6SN7(6N8P,etc) tubes produce visible light when in operation, i.e. was seeing no glow a proper assumption of malfunction.
 
2. Could a bad tube do any damage to the actual device. Seeing as how I left it on for 20-30 minutes.
 
Regards.

 

[Deterministic]

Added a picture of the cloudy residue at the top of the tube.
 

 

[Skylab]

Normally that "cloudy residue" should look more like a silver - that is the getter flashing, which is totally normal when it's more of a silver color. That could be a sign the tube lost it's vacuum. But if you see NO glowing whatsoever, the tube is dead. Best to get a 6SN7 somewhere else and try that.

 

[mrarroyo]

Correct, it looks like it is time for a new tube. 

 

[Deterministic]

Thanks for the replies guys, I ordered a set of NOS RCA 6AS7G and 6SN7GTBs to replace the stock tubes, hope everything works once they arrive. 

 

[Jim Spec]

I am using the 6AS7G in my Darkvoice with very good results.