Blues Junior tubes failing frequently?

[ktk7878]

Hello, to begin with, I'm not really experienced with tube amps and I need some help/suggestion.

I've bought a Fender Blues Junior IV amp around 3 years ago. During the first day of my ownership, it has been RMA'd because of a tube failure (tube sparking + amp making loud noises) which looked and sounded like the problem in the linked video. After it was fixed and sent to me, after like 2 years it happened again. Is this just a tube failure (and I'm that unlucky to chew through 2 sets in 2 years), or this is a symptom of some different problem with the amp?

https://streamable.com/lm907q

[martin manning]

Depending upon how much use it gets, two years could be considered normal life. That said, Blues Jr are generally set up with high idle current from the factory, so many people will modify the bias circuit to add a trim pot to dial it down a bit. You should be checking and resetting the idle current with each tube change, so having a bias trimmer is a good idea in general.

[JD0x0]

The BJ runs those EL84's way too hard. My friend won one in a contest and lost a power tube in under 6 hours of use.

Suggested mods are cool the bias down, increase screen grid resistor value (and wattage) and elevate them off the PCB. This will help significantly with tube life. While you're at it, you can upgrade the rectifier diodes for reliability, because Fender thought it was a better idea to save $0.01 per amp using underrated parts.

[dyker124]

Definitely the bias, but first, if you are in the UK make sure the mains transformer is set to 240 VAC. They are usually set for 230 VAC for the UK market which makes the valve heaters run over-voltage.