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Post by zdogma on Jan 9, 2009 19:33:14 GMT -7
I put in a fresh set of GT EL84's today, sounded great for about 30 seconds, then the power went way down, dove for the off switch and managed to prevent anything internal getting fried. I looked in the back and 1 was cherry red (after 1 minute on standaby and 30 seconds of playing)
I have terrible luck with EL84's, doesn't seem to matter if they're JJ branded or GT. I have had problems with 4 different EL84 amps (2 Dr.Z, a Peavey and a Fender), so I'm pretty sure its not the amps.
I have bought 3 quads and 11 pairs in the last 3 years. 1 quad had a redplate tube immediately, 1 quad shorted after 60 days. Of the pairs 3 have been bad right out of the box and 1 that went about a week later.
7 bad pairs out of 17= 41%
And those are supposedly "tested tubes" GT and JJ brand labelled are pretty much equal. 3 different dealers, also. Is this universal?
I wonder if shipping to Canada causes more failures (bad weather and the like)?
In any case its a good lesson, always try new tubes while they're under warranty. Thankfully these ones were.
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Post by fastfrets (Bob) on Jan 10, 2009 0:05:59 GMT -7
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Post by Deleted on Jan 10, 2009 1:14:38 GMT -7
I get my EL84's from the tubestore in Hamilton. Haven't had a bad set yet.
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Post by zdogma on Jan 10, 2009 5:42:32 GMT -7
I've had pretty good luck with the Tubestore, too. It is one of the companies I've bought tubes from, I've had 1 bad set of EL84's from them that was replaced for free.
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Post by Phil (aka Phil) on Jan 10, 2009 16:29:04 GMT -7
That's true if you don't use "graded" tubes from a good vendor that spec out in the range that your amp's cathode resistor is sized for. The resistor Z uses is will work optimally with GT #5, #6, and #7. Eurotubes has their own scale; I think it's a #28 that I buy, and it's close to a GT #6. If you just go to a vendor that doesn't grade their tubes and order them, you could be putting the equivalent of a GT #2,4,8,10... you just don't know. You could be inadvertently "setting" your amp's bias too cold or too hot. It's kind of bad that cathode biasing got labelled "auto biasing" or "self biasing"...which leads a lot of people to assume that you can throw any tube in there and it will work. You almost picture a little servo in there dynamically adjusting the bias with a little feedback loop The truth is that a given tube will reach the desired bias point only with the correct cathode resistor. I've gotten plenty of bad EL84's too... GT ones. Ever since I started ordering from Eurotubes I haven't had a single bad one. They're the exact same tubes as the GT, but I think Euro must burn them in better
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Post by jiseman on Jan 15, 2009 10:55:09 GMT -7
Let me preface by saying I'm fairly ignorant of GT tube numbers.
So with that out of the way, I just got a used Mazerati (post 2003 Mod) and it came with GT Red #4's in the EL-84 positions. I gather from Phil's post that this is a bad thing. Should I be looking into 5's, 6's or 7's? I'd of course like to get the most out of my amp.
I also think that the preamp tubes were replaced with 12AX7's (which I assume is fine). I don't recall the rectifier tube but now I'm worried that someone swapped it as well. I'll have to check on it....
Also, if there are other el84 recommendations (that I could actually get four of) I would be open to hearing those.
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Post by Deleted on Jan 15, 2009 11:35:15 GMT -7
Anything in the range from #4-#7 should work fine. To quote Myles Rose, "The medium numbers are the most versitile, will drop into most amps and be very close to most factories bias settings, and are the best general choice for most players wanting a versitile well rounded amp." You can learn more about the ratings at this link. www.guitaramplifierblueprinting.com/groovetubes.htmlYou can also post a question to Myles in Ask Myles in the Ask the Experts here on Z-Talk. Happy reading.
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Post by Deleted on Jan 15, 2009 11:43:01 GMT -7
There are some tube vendors that are highly recommended when retubing your Z as well. Mike is a forum member here. kcanostubes.com/categories/399/1/Home.htmand another www.dougstubes.com/tell these guys what Z you have and you are looking for a set of EL84's rated at #6 on the Groove Tube scale and they'll set you right up.
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Post by jiseman on Jan 15, 2009 12:04:33 GMT -7
Thanks a lot for the info, I will definitely check that out!
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Post by Deleted on Jan 15, 2009 14:59:30 GMT -7
Thanks a lot for the info, I will definitely check that out! You are welcome.
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Post by jiseman on Jan 15, 2009 17:29:07 GMT -7
Wow, lots of good information in those pages. I've spent about an hour combing them today.
Also, when I got home I checked the tubes again and sure enough, not stock. The GT EL84's our #4's, the Preamp tubes are both Phillips JAN 12AX7's (which should sound great I imagine) and the rectifier is a JJ EZ84 which I don't know anything about. Can anyone dropping by the thread tell me about the characteristics of this particular tube? If not no biggie, I'll drop a post in Myles' section.
Thanks again Doc001!
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Post by beauzooka on Jan 15, 2009 18:55:34 GMT -7
jiseman - do you mean the JJ GZ34? If so that is a decent rectifier tube. A lot of folks here will suggest that you upgrade to a USA 5AR4/GZ34 or some European equivalent. Spendy to do that though!
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Post by jiseman on Jan 15, 2009 21:52:27 GMT -7
Yes, GZ34, apparently I can't type and eat dinner at the same time :-)
Thanks for the info!
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Post by Deleted on Jan 15, 2009 22:29:53 GMT -7
Spending a little more on a NOS rec. is well worth the investment. You get a tube that will in all likelyhood last the lifetime of the amp. Or you can buy current production rectifiers once a year, every year because that's about as long as they will last. The NOS will actually be within proper spec.. Any current production rec. will not. Ask Mike about a good NOS rec. when you get those EL84's.
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Post by jiseman on Jan 16, 2009 11:27:03 GMT -7
I will likely do that. I still haven't got to plug in the Rati yet as my cab is at the Studio in the burbs and I won't be back there until Sunday. Once I get to do that I'll know more.... but considering I play with pretty hot humbuckers, I think the 4's will break up early on me (fine for the studio, but not so much for the gig).
I imagine a good rectifier is worth the purchase. I've been only semi-satisfied with my rig for the last couple of years and am currently on a "tonequest" of sorts. Hence the Rati purchase and the Z 4x10 cab purchase. I figure if I'm going to make all those adjustments in gear, might as well upgrade the rectifier while I'm at it and do it right from the beginning.
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Post by Deleted on Jan 17, 2009 20:22:37 GMT -7
Try the new tubes out and let us know what ya' think.
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Post by Phil (aka Phil) on Jan 18, 2009 11:40:52 GMT -7
The GT #4's are a little on the "low end" of the tolerable range, but they'll work. You may notice that it breaks up a little sooner than say, a 6 or 7. The difference in one number grade, say from 6-7 or 5-6 is not a huge one. "4" vs. "7" is a decently big jump. The 7's will stay cleaner longer and may be a little louder.
I've had "5"s that seemed cleaner than "6"s many times.
Like I've said before, I get all mine from Eurotubes now and ask for grade 28. They're the same tube as the GT (from the "Tesla" factory).
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Post by zdogma on Mar 28, 2009 9:08:44 GMT -7
So had another one go belly up on me, this time with the Mazerati GT. Less than 10 hours on a new set of GT EL84S, was playing some tunes at a jam session and all of sudden things sounded all thin and tinny.
Looked in the back, one of the power tubes was red, the others were cold/not glowing. Shut it down, replaced the bad tube with another GT EL84S (#6) and beck up and going in 10 minutes.
What have peoples experiences been with the NOS EL84's? DO they quit this often?
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Post by John on Mar 28, 2009 9:23:42 GMT -7
I know the Doc said the GT is very hard on power tubes.
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Post by BW on Mar 28, 2009 14:35:30 GMT -7
I've used/abused the GTEL84's (#6 or sometimes 7 if I can't get 6) in a MAZ Senior and/or Studio Deluxe for prolly 12 years, never had a bad 'new' tube, but man, when they are at the end of their work cycle and are ready to go, they will GO, right in the middle of yer big solo. I retube every tour and take a spare set w/ me. (fun gettin' 'em thru security.)
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Post by zdogma on Mar 28, 2009 17:10:41 GMT -7
I know the Doc said the GT is very hard on power tubes. Yeah, I've noticed that. My first set of power tubes had pretty much had it by 50 hours, they sounded flat and the GT logos had all turned brown over the plates.
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Post by zdogma on Mar 28, 2009 17:15:50 GMT -7
I've used/abused the GTEL84's (#6 or sometimes 7 if I can't get 6) in a MAZ Senior and/or Studio Deluxe for prolly 12 years, never had a bad 'new' tube, but man, when they are at the end of their work cycle and are ready to go, they will GO, right in the middle of yer big solo. I retube every tour and take a spare set w/ me. (fun gettin' 'em thru security.) Yeah, I wonder if its our vendors up here in Canada, or the shippers that cause all the bad tubes. I've had problems with the GT 6V6's and KT 66's as well, not so much as the EL84's, but more than most people here report. Once I get a good set they seem to last a long time, and most of the sets have been covered by warranty, so no big deal I guess.
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Post by kidbronze on Mar 29, 2009 18:31:13 GMT -7
Bob at Eurotubes... www.eurotubes.comEmail him and he'll fix you up. Good guy and excellent customer service. Have NEVER gotten a bad tube from him. Ships fast, too.
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Post by myles on Mar 30, 2009 11:23:01 GMT -7
I have some clients with cathode biased EL84 amps that change the output set after ten shows ... about 30 hours if you count sound check and general messing around.
As a side note, when the output tube set is swapped we all hear a difference.
On grid biased amps such as a Z-28 with 6V6 tubes they can last years, thousands of hours.
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Post by Phil (aka Phil) on Apr 2, 2009 9:00:19 GMT -7
Some Z EL84 amps are harder on the EL84 than others. The MAZ Jr NR seems to go through 'em pretty quickly, but amps like the Ghia and MAZ 38 seem easier on the tubes. The GT is a EL84 torture machine, but oh does it sound good
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