gene
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Posts: 115
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Post by gene on Feb 23, 2015 21:37:28 GMT -7
Hi all!
Lots of people are asking themselves when they should change tubes. I was lucky, I had no doubt regarding the answer when I heard and saw this happening to my Maz18nr:
I'm glad I didn't wait. I have now a new pair of EL84s and everything is back to "normal."
I hope you'll find this useful for future reference!
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Post by thunderstruck(formerly doc001) on Feb 23, 2015 21:55:16 GMT -7
Very useful. Thanks for sharing.
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Post by DRZ on Feb 24, 2015 3:54:50 GMT -7
Very helpful Gene. This visually describes what happens when a tube " Cherries Up " or fails due to run away plate currant. Quick replacement set and all is good again.
Should be a sticky.
DR.Z
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Post by greenblues58 on Feb 24, 2015 4:12:13 GMT -7
I have had this happen a lot as l have four EL84 based amps but particularly with my 1974x but only once with the maz. Does it do any harm to the amp?
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Post by Maddog on Feb 24, 2015 5:28:26 GMT -7
^^^^ It will usually blow a fuse before it harms the amp. However, anytime you see one "light up" or "red plate," it's always best to cut the power to the amp immediately and re-tube.
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Post by BritInvasion on Feb 24, 2015 7:51:05 GMT -7
Always makes for a couple of minutes of excitement when they unzip.
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gene
Full Member
Posts: 115
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Post by gene on Feb 24, 2015 7:59:23 GMT -7
Thanks all for your comments. Thanks Dr Z for your input! No harm was done. After changing both tubes, everything is back to the way it should be: no more crackling, popping sounds, no more hot "smell" and cherry color! I believe I was lucky because I heard those pops and stopped playing (I was just practicing on my own in the attic- a rather "cosy" place ). But I didn't turn the amp off. What was a definite alarm bell was the smell (not a burning smell, rather a type of very hot smell- really like a very hot clothe iron) that made me think about the tubes. I looked at the back of the amp and I saw that beautiful cherry red EL84 glowing back at me! I finally put the Maz on standby. I'd say the whole thing lasted no more than 2 minutes between I started hearing crackling noise and turned the standby switch. Was the tube red plating before I heard the noise, I don't know. Then, that's when I started playing with fire... and I did that movie (I like to document and share...). I read somewhere that the resistor connected to the EL84 (screen resistor?) is the one that will sacrifice itself (in case the fuze doesn't brake) and protect the output transformer when the tube redplates for too long. It did not happen in my case. This was about a week ago. Here is a picture (I hope you can see it) of my new tubes in action: no more red plate and hollow, crackling sounds. Those are the Russian 6N14N-EB tubes. Dr Z mentioned them in a thread recently: built like a T34! (Really, they are heavier in weight than the Electro-Harmonix they are replacing.) Long live rockn' roll!
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Post by Papa Juan (lanier816) on Jun 12, 2015 19:17:54 GMT -7
I had an 84 go bad on me this morning. I was pushing my amp way too hard, I've never pushed it that hard before and will most likely not do it again. Once I was through playing I had all these pops and it sounded like someone was shuffling paper, real staticky. Luckily I remembered I had a spare set of 84s in my storage unit (after a minor freak out of course). One my way to my storage unit I ordered a replacement set, I'll be better prepared next time. My tube didn't look like it wanted to explode like yours though, yikes!
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Post by pcns on Jun 13, 2015 15:32:35 GMT -7
Nice video!
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Post by LT on Jun 15, 2015 12:26:59 GMT -7
Thanks for sharing Gene….very useful and informative.
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gene
Full Member
Posts: 115
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Post by gene on Jun 15, 2015 14:31:33 GMT -7
Thanks guys, glad you liked it!
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