Blowing tubes consistently - why?

[DHerbert]

I am still new to tube amps, so bear with me.

I got a 65 PRRI in summer 2021. Blew a power tube in Feb 2022 - just 7 months later. Had it all checked out and tube replaced. Blew the same tube in December 2022, just 10 months later.

Borrowed my brother's (excellent) VOX 15 in December. Blew a tube in that about two weeks ago, after only playing it for a month.

What is happening? Is there something in my signal chain that could be doing this? I mostly play a 2020 Telecaster, through a variety of pedals. Could it be a pedal?

I play every day, it's true, but it's not like I am gigging or cranking these things like mad. Based on what I read, these tubes should not be burning out so often. Any thoughts?

 

[schmee]

Hard to say really, but provided tubes in new amps are likely "the lowest bidder". They certainly were 10 years or so ago. That can mean they are OK, but it can also mean they are not, depending on which they are. But your experience is highly unusual, however I seriously doubt it's anything you are doing... unless you have unusually high wall voltage.....? Do you have a way to check that? It may vary throughout the day....

 

[Peegoo]

The only way to know is to test voltages.

-Into the amp from the wall receptacle

-From the PT secondaries

-From the rectifier and filter caps to the tubes

 

[printer2]

Bad mojo....

 

[DHerbert]

Hard to say really, but provided tubes in new amps are likely "the lowest bidder". They certainly were 10 years or so ago. That can mean they are OK, but it can also mean they are not, depending on which they are. But your experience is highly unusual, however I seriously doubt it's anything you are doing... unless you have unusually high wall voltage.....? Do you have a way to check that? It may vary throughout the day....

Wall voltage is a good tip - will check, thanks!

 

[DHerbert]

The only way to know is to test voltages.

-Into the amp from the wall receptacle

-From the PT secondaries

-From the rectifier and filter caps to the tubes

Yes, will check wall voltage - that is a consistent element here....

 

[ps_electrik]

Did you you use a matched set and re-bias the power tubes after replacing?
This is necessary for power tubes to optimize performance and life.

 

[badscrew_projects]

They might be over biased (conduct too much current and overheat)

 

[tacobender]

Do the amps share the same shop tech?

 

[11 Gauge]

Bad mojo....

I'm guessing this is the cause, or simply bad luck.

Also, what is specifically meant by 'blowing a tube', and has it been exactly the same thing every time?

Assuming these are power tubes that are redplating at some point before they actually completely fail, I'd certainly check the wall voltage.

I thought that Fender has pretty much been known to bias their RI amps on the cold side, so the wall voltage would really have to be high.

If the PRRI doesn't have JJ 6V6Ss in it, I'd definitely replace them with a matched pair. They can take a good bit of abuse, IME.

 

[Jakedog]

Sometimes bad stuff just happens. I went twenty years without an amp failure, then blew up seven in one year. Haven’t had another amp failure since. Never did change anything I was doing.

 

[Bobbyoso]

When you say you "blew" these power tubes, what does that mean? Did they explode, or redplate, or did output fade away, with either clean or distorted fades? Or is output nominal, but with hums, crackles, unexpected distortions, dropouts, or frequency loss?

How the tubes fail is pretty useful in determining what's wrong. The only thing that comes to mind (I'm no tech, just a guy who's been using tube amps for 55+ years) that might cause failure across 2 different amps is perhaps you have the output on several pedals (especially od/gain pedals) set very high, so perhaps the input levels are way out of spec.

Interesting issue.

 

[Burning Fingers]

I have seen too many "blown" output tubes that were damaged by the power cord or foot pedal being tossed in the back of the amp after use. The loss of vacuum in the tubes due to a crack in the glass envelope was the giveaway.