Do preamp tubes blow ? How do they fail ?

japster · Mar 20, 2011

Hi,

My studio pre amp started going fizzy in a gig last night then within the space of about 5 songs got weaker and weaker until there was no sound at all.

I've opened it up today and the tube at V2 position has gone all silvery black inside between the Mica spacers at the top. I'm assuming it's gone and will substitute another tube to check but I'm wondering what's caused this to happen and would it happen again with a new tube ? V2 is the Rhythm 3rd Triode / Lead 5th Triode and explains why I was left with no sound at all.

So is this just a normal tube failure or is there something wrong with my pre ?

Also any recommendations for replacement tubes ? I play mostly rock with high gain leads.

PG13 · Mar 20, 2011

Definately check the tube first. If it's powdery white like you say, you've lost vacuum and the tube is shot. This is the least expensive way to trouble shoot a pre-amp. Sometimes you will get a new "dud" tube when you order tubes. It doesn't happen often, but it does happen. I buy tubes from the tubestore.com (Canada) and tubedepot.com (USA). They have always without question replaced tubes which arrived that did not work. As for what tubes to get, both websites have very comprehensive tube comparison charts, reviews and details on how they manifest themselves when in use. I currently have JJ's in my Triaxis and 2:90. I have no complaints.

japster · Mar 20, 2011

Thanks,

will check them out

MrMarkIII · Mar 20, 2011

Silvery black is not the same as powdery white. The former is normal, the latter means loss of vacuum.

japster · Mar 21, 2011

Yeah the tube turned out to be fine after all,

Both my EV speakers had blown. I mean how can 2 x 200w cones melt under the load of 1 channel of my 295 power amp ? 1 x 95 watt ?

Sending them back to the recone guy !