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Author
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Topic: Tube swapping question?
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David Higginbotham
Member From: Lake Charles, Louisiana, USA
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posted 25 November 2006 06:26 PM
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I currently have a Carvin XV-112 100 watt tube amp that has a set of Groove Tube EL-34's & a set of Russian (Mullard?) EL-34's. I have seen these amps for sale with 6L6's installed. My questions:
1) Can a 6L6 tube be used as a direct replacement for an EL34? I think I've read where it can be, but not the other way around. Do I have to rebias if so? 2) What improvements can I expect by changing the tube type. The amps sounds great as is! I have replaced the 12 inch speaker with a JBL K-130-4 and it made a signifigant difference. Should I go by the rule if it ain't broke don't fix it?
Thanks,
Dave ------------------
GFI D-10, Evans FET 500, Carvin XV-112 w/ JBL K-130 [This message was edited by David Higginbotham on 25 November 2006 at 06:40 PM.]
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Mike Fried
Member From: Nashville, TN, USA
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posted 25 November 2006 11:06 PM
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Unless it's a cathode-biased amp designed for swapping tube types, it will need to be re-biased if changing to 6L6s, although that's the only mod it should require unless the plate voltage is over 450v or so (yes, visa-versa is indeed a different story). Other things being equal, the 6L6 has more of a "hi-fi" full-range sound as opposed to the EL34's increased midrange and softer highs. IMO, if you want more clean power, I'd go with KT77s, 6CA7s, or maybe 6550s instead of 6L6s, and take advantage of the increased headroom. In any event, I'd have any power tube conversion done by a tech unless you're experienced in tube amp work.[This message was edited by Mike Fried on 25 November 2006 at 11:15 PM.] |
Jim Sliff
Member From: Hermosa Beach California, USA
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posted 25 November 2006 11:58 PM
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A rebias is necessary even if you replace 6L6's with other 6L6's...or any other tube with the same type...but especially when changing types.Your Russian tubes are NOT Mullards, which were European tubes. Groove tubes could also be Russian - but are you saying you have two pairs of different types? If so, ge them out of there and get a matched quad of tubes, and have the amp biased by a professional. Mismatched pairs of tubes in a 4-power tube amp are a bad idea in most cases. In this case it IS broke, so fix it! ;-) 6CA7 is simply American nomenclature for the EL34, and the KT77 is a slightly higher-capability (but not power) EL34 as well. Same tube, essentially, and will NOT give you more of anything (except dollars in the tube seller's pocket) - but changing your tubes is a good idea, especially when you're dealing with Russian tubes, which usually aren't real EL34's but instead some other tube with close specs. 6550's in that amp will draw far too much heater current and should not be used without an auxiliary filament transformer - hardly worth it. Either go with a matched quad of EL34's or 6L6's...and IMO stay away from Groove Tubes, who are just a repackager, not a full-scale manufacturer. Even their "Made in USA" 6L6GE is mostly made in China with some US components. In a very generalized way, EL34's give you a more "Marshall-like" British sound - more upper mids, less bass. 6L6's give you lots of bass and highs (although the highs are smoother) but more of a scooped-mid sound. Any of those will give you plenty of clean headroom if they are biased correctly. You can also increase headroom a bit by replacing the preamp tube for whatever channel you use with a 5751 instead of the stock 12AX7. |
David Higginbotham
Member From: Lake Charles, Louisiana, USA
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posted 26 November 2006 07:33 AM
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Mike & Jim, thanks for the help. Although I have performed limited work on amps, I am certainly not considered an amp tech. I am fairly new at the tube amp stuff. I haven't had this amp very long and I was going to get me a matched quad of power tubes to replaced the ones currently installed. The preamp tubes are new and are 12AX7's. I have a host of preamp tubes to try different variations in sound. Also the reason I thought it may be Mullard was because they are ruby colored. After your comments, I don't believe it is worth the extra effort to change tube types. I get a really good sound with the EL34's and plenty of headroom. The amp has a 3 & 5 band EQ's so there is a great deal of control. Your personal recommendation for replacement power tubes are?
Thanks,
Dave |
Jay Fagerlie
Member From: Lotus, California, USA
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posted 26 November 2006 08:20 AM
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David,
Depending on how old the amp is, some newer X series amps had a switch to change the bias when swapping tubes. The switch would be on the back panel.
If it is older than that, it has probably been modded. The mod from 6L6 to El34 is not a really complicated one, and to use 6L6's in it again, you will probably need to only re-set the bias.
If you are getting new tubes for it anyway, any music store should do the re-bias with a tube swap for no more than $20.00. In the store I tech at, if someone buys the tubes there in the store, I don't charge to re-bias....it's a really simple procedure that should take no more than 5-10 minutes.
I had the X-100 twin stack back in the 80's....I sold the head and one of the cabs, now I've been looking at getting another one-I think it would sound good with my steels....live and learn....
Jay |
Mike Fried
Member From: Nashville, TN, USA
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posted 26 November 2006 12:12 PM
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Just to clarify, although EL34s and 6CA7s are listed in tube manuals as interchangeable (they do share the same pinout and many specs), the American-made 6CA7 was a very different tube from the European EL34 and was very much a "6L6 on steroids" in character. They required very different grid bias settings, to the tune of actually replacing the bias load resistor feeding the adjustment pot, when using a '70s Music Man with EL34s instead of its original 6CA7s. The point being, there are currently-made 6CA7s that are modeled more after the old American (Phillips/Sylvania) tube (and sold as such), and do provide more headroom and "American" character than the EL34. They would be the alternative I personally would choose first over a 6L6 or an EL34 for pedal steel in a 100w amp. Or on the other hand, if you're really satisfied with the sound you're getting, never mind! Do make sure the amp is correctly biased, though, for whatever tubes are in there. |
David Higginbotham
Member From: Lake Charles, Louisiana, USA
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posted 26 November 2006 01:16 PM
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Mike, again thanks for the input. I very well may just stay with a matched set of EL34's. I am very satisfied with the sound I am getting. With comparison to the Fender Twin Re-issue I used to have & the Hot Rod Deluxe I still have, it is better in the mid range and smoother on the highs. It has plenty of low end response as well using the 15 inch speaker.Jay, I must say that trying the Carvin for steel was really Darvin's idea. I read a post here on the forum where he had tried one with 6L6's and he stated it was one of the best steel amps he had used. I must admit I agree with his findings as well. Here is his post: http://steelguitarforum.com/Forum11/HTML/007576.html
Here is mine in the background:
 I am now looking at which brand of power tubes to use. Research shows JJ's to be good as well as Electro Hormonix. But I believe Brad Sarno was using JJ preamp tubes and they started having some problems. Any input is appreciated.
Thanks,
Dave |
David Higginbotham
Member From: Lake Charles, Louisiana, USA
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posted 26 November 2006 05:05 PM
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Got a set of JJ's EL34's on the way. Thanks for the help guys! This one can be closed.
Dave |
Jim Sliff
Member From: Hermosa Beach California, USA
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posted 26 November 2006 10:31 PM
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Good call on the JJ's.Re the 6CA7 vs EL34, what Mike said is not untrue, but neither was what I said - many of the 6CA7's and EL34's were the same tube with a different name, and i got worse in the 70's, then exponentially worse in the 80's when you couldn't be sure WHAT you were getting. My point was regarding NEW tubes, and I guess I didn't clarify it enough. NOS tubes Mike's talking about are different. Newer tubes - it's a crapshoot. | |
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