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AUDIO FORUMS >> General Discussion and Support >> A Brilliant Flash - and then nothing.
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Message started by honkytonkwillie on 01/02/16 at 04:24:37

Title: A Brilliant Flash - and then nothing.
Post by honkytonkwillie on 01/02/16 at 04:24:37

Rachael is my 24x7 amp until Christmas break each year, where she gets pushed aside for a 2-3 week rest to make room for the tree and stuff.

My college age daughter is home for the holidays, and she noticed the pretty tubes and started asking questions. I told her the tubes looked even more beautiful when the amp is powered up, so I hit the power switch and got a BZZZZZZT! sound with a big white flash from the rectifier.

Uh-oh.

Immediately I realized there were no speakers attached, resulting in the amp seeing zero load. I seem to remember reading about not doing that...

So I unplugged her, hooked up some speakers, and got nothing. Then I swapped in a working-when-I-took-it-out rectifier tube, and tried it again, and got nothing.

Time to read the manual (which many consider cheating). Ah! It has a fuse! Two actually, one is just a backup. Sure enough, her fuse was blown. Replaced it and she powered up just fine. Yay!

Next, I powered her down and swapped in the original rectifier to see if it was toast. BZZZZZT!

Yup. That tube's a-goner. Along with my second fuse.

Live and learn.

Title: Re: A Brilliant Flash - and then nothing.
Post by hdrider on 01/03/16 at 16:39:26

Always have some back up tubes and fuses. Glad your daughter was interested in tubes and open to the magic they can produce.

Title: Re: A Brilliant Flash - and then nothing.
Post by honkytonkwillie on 01/25/16 at 11:13:36

I'm less than 50 years old and already she's asked to inherit a particular set of speakers when I die. A real charmer, she is.

Title: Re: A Brilliant Flash - and then nothing.
Post by honkytonkwillie on 01/25/16 at 11:27:03

I set up the amp again with a backup rectifier tube after Christmas break. Three hours into operation, I peeked at the bias meters and saw the left one was pegged and the right one was right at 41mA where it always is.

Music didn't sound disturbed or anything, so I shut her down and swapped sides with the EL34 tubes. Powered up again to see the right meter peg. Hmmm. Bad tube I guess.

Fortunately some high-mileage EL34's volunteered to come out of retirement, so I'm back in business.

Questions: 1) The brilliant flash which killed the rectifier, might it also have damaged an output tube? Only one output tube and not the other?

2) How long do output tubes last? This dying EL34 lasted 4099.25 hours. (I keep meticulous records).

(For a $40 tube, that's just under $0.01/per hour of operation.)

Title: Re: A Brilliant Flash - and then nothing.
Post by Lon on 01/25/16 at 12:23:54

Amigo, I think that tube was aged and vulnerable and the rectifier blow took it down.

That's a lot of hours on a tube! You got your money's worth.