Tube info

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Post by joshwilson3 » Sat Jul 02, 2005 4:07 am

I've got a stock UK model 1983 JCM800 2203 with EL34 tubes.

I know that there is a certain bias range, and if you get tubes that need more juice you have to replace some resistors. So, from all the tubes mentioned, what resistors would each type need in my amp? Could I use KT66 and KT88 tubes off of the same bias resistors?


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Post by bob barcus » Thu Sep 15, 2005 4:24 pm

:roll: I always thought that nos Mullards ef-4 single halows were the best tubes? On ebay they seem to bring the highest bids.Thanks Men of Metro!

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Post by SB Monster » Mon Oct 31, 2005 6:39 am

bluefuzzguitar wrote:
Billy Batz wrote:Ive been thinkging about a 6CA7 quad for a long time now. Has anyone else used both a 6CA7 and Mullards and can you comment?
I currently have a quad of 6CA7's in my Super Bass. The GT KT66HP's that were in there gave up the ghost last week (fried a resistor too!). In a way I'd been waiting for that moment because I was smart enough to have bought a quad of 6CA7's and KT88's in advance so I could hear what they sound like in my Super Bass. The 6CA7's that are currently in there are exactly as I described in my post in which I break down the various tube types I know the sound of. In other words: dark, bass-heavy but without sacrificing the highs, EL34-like mid grind coupled with 6L6-like glassiness, a true British/American hybrid with plenty of headroom. I like the sound of these tubes a lot and I can recommend them, Dan!

Following on from Mike,

FYI, I ran a quad of GT 6CA7's in a SuperBass recently and changed them to GT KT66HP's only last week. Mikes descritions are completely accurate in all respects. It is a matter of opinion which one is better with the answer being "in the ears of the beholder".

IMO the 6CA7 sounded more transparent and "fender-ish" than I would have liked but with bags of headroom/huge soundstage which makes for a gorgeous rich dark mid and low end grind.
The KT66 is different in that they produce a more detailed and wider mid range growl still with all the headroom but sounds more "marshall" and definitely more british to my ears.

One thing I am sure of, they're both excellent sounding tubes,either of which are very well worth trying as an alternative to current production EL34's and if you're using one or more drive/fuzz/boost stompers in front of you're amp the differences from EL34's will be even more pronounced.



Post by Guest » Fri Nov 04, 2005 12:07 am

i'd like to add to that most excellent tube review, for anyone new to the world of tubes, that although the tubes mentioned all have the same base (i think) you cannot just put any of these 8 tubes in your amp . it must be biased and possibly moded for some of thes tubes described. ie, i've never heard of or saw a set of 6L6's in a marshall..would be cool tho!

may be someone of authority could comment on that subject a little more thoroughly than i?


on a side note, that awsome tube type review has inspired me to ask this question:

how can i get a set of KT66's in my JTM/JCM 800??? is this a direct swap or are mods needed?

[truely, a GREAT review. good job!]

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tube swaps

Post by Marshall (no, really) » Sat Nov 12, 2005 9:45 am

I drop by here once a week or so to have a look around, and today this thread happened to be back up top. Great reading.

While I appreciate the tone analysis of the tubes, I was wondering of someone could supply more info of a technical type. For Example:

Which of these tubes are direct swaps? I think 6L6GC and 5881, for example, just need a bias adjustment, and the same applies to EL34 and 6CA7. But 6CA7 and 6L6GC are not interchangeable in all but a select few amps (THD Univalve, eg).

Is there a mod one can make to allow the interchanging of 6L6GC and EL34 types, or is the difference more than just which pin connects to what? Is it just not possible? Not practical?

With proper adjustments and individual bias pots, could a real nut match EL34s and 6L6GC in a fifty watter, just to see what happens?

Just looking for tech discussion. Thanks


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Post by The Pup » Sun Jun 29, 2008 7:28 pm

Great thread full of informed responses. Thanks.

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Post by jctaudiodesigns » Tue Jul 01, 2008 9:16 am

The one tube that is missing from this tread is KT77, anyone want to comment?
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Re: Tube info

Post by razelfrax » Fri Dec 05, 2008 8:23 am

I just bought a Traynor Voicemaster that is the twin of the one I already have . They have all the same components and I have wired them identically as mostly 1986 style. However the one I just bought (400$Can) came with 4 Mullard l63 ecc83's and a pair of Mullard xf2 single halo EL34's with lots of life left in them. The other one has Mully pres and Shug KT66's . Northern Electric and I thought they sounded very very close. Maybe this weekend we can make a few clips and post them.
Very rough Demos lol" onclick=";return false;
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Re: Tube info

Post by ashfender150 » Thu Dec 11, 2008 7:26 pm

is it true that when you purchase tubes that you have to "break them in". because to my ears, every EL34 power tubes i've purchased for my amp sound kind of thin in the first week of ownership and even give off a slight smell. then once the smell stops about 2 weeks in, they seem to have been "broken in" and sound full?

any thoughts?" onclick=";return false;

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Re: Tube info

Post by capkutay » Tue Nov 17, 2009 3:12 am

Thanks for the post, really helpful.

What if I'm trying to recreate that Jimi Hendrix marshall sound?

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Re: Tube info

Post by Structo » Wed Nov 25, 2009 11:02 am

ashfender150 wrote:is it true that when you purchase tubes that you have to "break them in". because to my ears, every EL34 power tubes i've purchased for my amp sound kind of thin in the first week of ownership and even give off a slight smell. then once the smell stops about 2 weeks in, they seem to have been "broken in" and sound full?

any thoughts?
Tubes do settle in after a few hours of playing them.
Typically a power tube will lose some of the high end harshness after 8 hours or so.

And as they age they will lose some high end frequencies.
You don't usually notice this because it happens so gradually and you will adjust the tone controls accordingly.

Double check your bias after two or three hours play time because it can drift a bit when the tubes are new.

Don't let that smoke out!

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Re: Tube info

Post by wrea398 » Sun Dec 06, 2009 3:21 pm

I still think that every single amp, even units of the same dates and components have different charcteristics. They all have thier own personalities. Amps with the same brands and values of caps and resistors will ultimately sound different due to drifting values, age and even player dynamics. I think the different tubes are best rated by that particular player in that partucular amp. These opions in here are a great starting point for the average Joe to get a baseline but only actual experience and YOUR personal ear will decide whats best for your amp. I like WINGED C and Mullards myself but I have a 71 Super Trem that has newer Svetlana EL34s and GE 12ax7s to me sounds better than any Mullard I have ever heard. ...My 2cents....

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