KT66's vs. EL34's: tone difference in a Marshall Super Lead?

billm408

Member
Not quite the same, but I just swapped out KT88's for the EL34's in my XTC and the difference is phenomenal! Wider, beefier tones through the gain channels and more depth and darker tones with the cleans. I should have done this years ago!
 

deeval

Silver Supporting Member
Supporting Member
If you have real NOS KT66 they will be very good for your tone,as it will make the amp more clearer and give it a nice fat bottom and the mids will not be harsh,reissue KT66 are also pretty good,I had tried both in my JTM45 and the NOS where better but they are very pricey.I like the KT66 better,But one more thing if you can get some Mullard 34,s NOS one,s then they also are their with the tone!
 

telewacker

Supporting Member
If you like beautiful chime try some big bottle Sylvania's,bestsounding EL-34's i've tried.
If your talking about Sylvania "Fatboys" they are not EL34s, but rather 6CA7s. They are a direct replacement for EL 34s but have a different internal structure. They are what EVH used on his early records apparently. And they are indeed great sounding tubes. I prefer them over EL34s, as well as 6550s-KT88s which I like better than EL34s but not as much as Fatboys.

http://www.cathedralstone.net/Pages/Syl6CA7.htm
 

4styx

Member
If your talking about Sylvania "Fatboys" they are not EL34s, but rather 6CA7s. They are a direct replacement for EL 34s but have a different internal structure. They are what EVH used on his early records apparently. And they are indeed great sounding tubes. I prefer them over EL34s, as well as 6550s-KT88s which I like better than EL34s but not as much as Fatboys.

http://www.cathedralstone.net/Pages/Syl6CA7.htm
Ya those are definately the ones!Cool link by the way.Are you that JC103 guy from GC?
 

imguitardan

Member
To install the Svetlana Fatboys or KT66/77/88's in a Marshall, do I have to do anything different internally or can I just plug them in and bias them and then go to town?
 

telewacker

Supporting Member
To install the Svetlana Fatboys or KT66/77/88's in a Marshall, do I have to do anything different internally or can I just plug them in and bias them and then go to town?
The Fatboys are Sylvanias, though they are often branded RCA, Phillips, GE, etc., and have been out of production since the 80s. EH makes modern reissues but they don't sound the same. They're not cheap but they are supposed to be the most rugged and long lasting so if you like the sound they're worth the money. They are a direct replacement for EL34s, so they can be put in any EL34 amp with just a bias adjust. Not so with KT88s or 6550s. I have no experience with KT66/77s but I'm guessing that they are like the KT88s.

Lee Jackson told me about the Fatboys and his take on them was that they combined the best of EL34s and KT88s, and I agree after using them.

For info on the Fatboys go here:

http://www.cathedralstone.net/Pages/Syl6CA7.htm
 

bosstone

Member
I have a pair of Sylvania big bottle tubes that have both EL34 and 6CA7 written on them. They are the well known Mesa labeled STR416 that were used in early Boogie MKIII Simul Class amps from the 1980s. I also have a pair of non "big bottle" Sylvania labeled tubes, made in England, that are also labeled "6CA7/EL34".
 

iama

Member
I have a pair of Groove Tube EL34's #5 in my JCM 900 combo and they sound just incredible. Big, warm and with that perfect Marshall grunt. I previously had the #6 level of the same tubes but these moved into the right area for me.

While I noticed the big difference with these tubes, I'm a novice. What would I notice against some of the tubes mentioned here? My point of reference are the Groove Tubes.

Thanks!
 


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