Recurring tube failure in SVT-3 Pro

[Todd McIntosh]

Hi guys,

I'm using a SVT-3 Pro head with my rig and it sounds great when it works. However the 12au7 preamp tube is repeatedly failing, I would say every 1-2months, and I only gig a few times a month.

Some other details. I have the head in a 3u Gator case which fits only the head, so there isn't a ton of ventilation space on the sides. When going to gigs, I try to be careful and not bump it too much, but it does get the occasional bump.

I know that tube amps are more susceptible to travel damage, but this seems really extreme. Could this be an actual electrical issue on the circuit board or some other internal issue? Or is just from usage? I don't recall anyone else on here claiming tubes going so fast on them.

Thanks for any help or advice you may have!

Todd

 

[beans-on-toast]

What you are describing is not normal.

The plate and cathode voltages of the 12AU7 should be checked against references on the schematic. Out of spec components in that stage could cause voltages to be off that could stress the tube. Too high a cathode current for example will shorten the service life of the tube.

Another possibility, if you are always buying replacements from the same place, maybe they have a bad batch of tubes.

 

[agedhorse]

Something is very wrong, you should be getting at least 3 if not 5-10 years out of a preamp tube. It's time for a QUALIFIED service tech to verify proper operating parameters of the amp.

 

[Todd McIntosh]

Thanks guys. It is true that I have bought the replacements from the same place, but the first one to go was the one that came with the head (which I bought used). I'll find a local tech that can take a look at it and see if they can figure it out.

 

[agedhorse]

Be sure the tech really knows his stuff and not just a place holder for the seat at the bench.

(I see the results of those "techs" who shouldn't be allowed anywhere near an amp...)

 

[Todd McIntosh]

For sure. I'm near Toronto, Canada so if you guys know any reputable techs up here, let me know!