Power Tubes

[Gtrjunior]

Last Saturday I powered on my amp (Quickrod) and let it warm up a bit. When I flipped the standby switch to “on” it blew a fuse. So I replaced the fuse and it happened again, this time I saw a bright flash coming from one of the power tubes. I emailed Scott and he said most likely was a power tube failure.
Before this amp I played a 2204 JCM for years. I have never blown a power tube like that. The Marshall always “told” me when they needed replacing. It would start making popping noises and minor volume fluctuations.
I reordered a set of tubes from Splawn and I also have a set of reissue Mullards on hand.
These tubes were what came from Splawn and have lasted almost 2 years. I posted about this on the Splawn board and Rhodes guys seem to think that the tube(s) died prematurely....
Ime, a set of tubes usually lasts about a year, maybe a little more with regular use.
Does anyone here think this is unusual?
Also, what is everyone’s experience with actually having a tube fail? When I visually inspected the tubes, I don’t see anything that looks abnormal....of course that doesn’t mean much.

Also, thoughts on a bad PI tube causing a blown fuse?
Thanks!!

 

[evan47]

Re: Power Tubes

Have your amps bias checked by a tech.

 

[Kamanda~SD]

Re: Power Tubes

Also depends on how much you're playing and the tube construction itself. I've had tubes last years and I've had tubes last 8months. However I would check the bias as well as evan suggested.

 

[Gtrjunior]

Power Tubes

Have your amps bias checked by a tech.

I know how to bias
Plus, at this point I can’t power on the amp without blowing a fuse so I can’t even check the bias.
It powers on but when I flip the standby switch to “play” mode the fuse pops

 

[Gtrjunior]

Power Tubes

Also depends on how much you're playing and the tube construction itself. I've had tubes last years and I've had tubes last 8months. However I would check the bias as well as evan suggested.

The stock tubes are Chinese EL34B
I typically use the amp for about 5-6 hours of moderately heavy use per week.
My basement is set up as the rehearsal studio so while I’m not blaringly loud, I’m loud enough to get over a heavy handed drummer.

 

[Gtrjunior]

Re: Power Tubes

I guess what I’m asking is about the sudden failure of a tube.
I’ve had tubes slowly fade away to unmusical functionality. But I’ve never just had one suddenly fail.

 

[Kamanda~SD]

Re: Power Tubes

It happens. However if putting in other tubes and it still blows, time to take it to get looked over.

 

[Jacew]

Re: Power Tubes

They can fail suddenly, modern tubes have quite a lot of quality variance. And since it already lasted 2 years, I wouldn't be alarmed about it.

Remove the broken tube and turn amp on to see if the fuse blows again. If it doesn't, change new power tubes and bias the amp.

 

[Darg1911]

Re: Power Tubes

I don't think it's unusual with current production tubes. I had 2 X JJ EL34's in my marshall build. I have a PPIMV installed. Changing the master volume level doesn't/shouldnt change the bias point of the tubes by any significant amount (less than 1ma). The tubes were a few months old and I was re-checking bias. I had a meter monitoring each tube and another monitoring plate voltage. The tube bias had drifted some but was still close enough (between tubes). Even though it really shouldn't matter, for consistency sake I try to remember to turn the master volume wide open when checking bias. I forgot to do so initially and I just happened to remember, so I cranked it wide open. I watched the bias of one tube change by almost 5ma. The other, less than 1 ma, as expected. After some head scratching, I swapped the tubes around and that 5ma change followed that same tube to the other socket. "Leaky" tube. I don't pretend to understand all the tech but from what I gathered, that tube would have most likely continue to go south and eventually would have run away enough to blow the fuse (at best). There was nothing obviously wrong, nothing I could hear when playing the amp. But the time probably would have come where, one day, the fuse would just end up blowing. And basically, I just got lucky finding it before it was a problem.

And finding out that my PPI Master Volume can serve as a rudimentary tester for excessive grid leakage? A bonus.

Point being ... stuff can be happening within tubes that we don't know about until a fuse blows (or worse). I try to check the bias every couple of months just to keep an eye on things. I realize that not everyone can do the same and not every amp makes it easy or even feasible. And basically, it still guarantees nothing.

 

[Gtrjunior]

Re: Power Tubes

Thanks guys.
I’ll swap tubes this weekend and if all goes well, rebias and take t from there.

 

[LLL]

Re: Power Tubes

Try a pair of EHX 6CA7s... for toanz.

 

[Gtrjunior]

Re: Power Tubes

Try a pair of EHX 6CA7s... for toanz.

Lol...I was looking at those. JJ makes a 6CA7 as well.

 

[Gtrjunior]

Re: Power Tubes

Ok...even though I already ordered a set of EL34 from Scott, I just bit on a set of JJ 6CA7 too.