KT-77 vs. EL-34/6CA7

JD · Post by JD » Wed Feb 08, 2006 8:48 pm

Has anyone compared a true beam KT-77 tube with the standard EL-34?

From what I read, the KT-77 handles considerably more power (32W vs 25W) and has a much tighter sound, especially in the low frequencies, more like a KT-88 vs 6550 or KT-66 vs. 6L6.

Bob at Eurotubes has the new JJ KT-77s coming in a week or so. I'm looking forward to trying these out! Will these simply install with a bias adjustment and no other mods in an EL-34 equipped Marshall? Or is this a bad idea?

novosibir · Post by **novosibir** » Wed Feb 08, 2006 8:52 pm

http://forum.metroamp.com/viewtopic.php?t=4315

Larry

JD · Post by JD » Wed Feb 08, 2006 9:39 pm

Thanks. I must have been sleeping, not sure how I missed that post.

I'm looking to get a bit more out of the bottom end vs. a standard EL-34 so maybe these will work well for me. I tried the EL-34Ls and while ok just a bit harsh on the mids and high end, for me anyway. I'd still prefer a standard EL-34 design. I'm really looking forward to trying these new JJs as they are the only current production KT-77, at least that I have found. Not sure where I'm going to bias them yet.

I'm warming up to the 6L6GC sound of the 5150 but just a bit too tight and clean for my tastes. Don't much care for the 6550s in Marshalls.

novosibir · Post by **novosibir** » Wed Feb 08, 2006 10:05 pm

JD wrote:I'm warming up to the 6L6GC sound of the 5150 but just a bit too tight and clean for my tastes.

A couple days ago I've supplied a customer's '91 SLO 100 with the new TungSol 12AX7's and a quad NOS Sylvania 6L6GC's, biased to 76% of the max. plate dissipation (no problem with Sylvanias)...

... the amp now is pure killer

Larry

JD · Post by JD » Wed Feb 08, 2006 10:34 pm

My only experience with the 6L6GCs is the 5150 and that amp is a monster. Way too much preamp gain on tap so you have to be careful, but with some patience it gives a nice big fat crunch. Pushing the power tubes with little preamp gain works well.

I have only played EL-34s and 6550s in Marshalls and definitely prefer the EL-34s. Sounds interesting to try a set of 6L6GCs, which is more or less what I was after with the KT-77s. How do the 2 compare in the same amp?

I know going from an EL-34 to 6550 can require a bias resistor change, otherwise its pretty much a straight swap, but going from an EL-34 to like a 5881 or 6L6GC requires more circuit changes. Are any amp wiring mods required to go from EL-34 to KT-77 (with the pin 1 not used) on a Marshall?

killertone · Post by **killertone** » Thu Feb 09, 2006 3:58 pm

JD wrote: I know going from an EL-34 to 6550 can require a bias resistor change, otherwise its pretty much a straight swap, but going from an EL-34 to like a 5881 or 6L6GC requires more circuit changes. Are any amp wiring mods required to go from EL-34 to KT-77 (with the pin 1 not used) on a Marshall?

There should be no mod necessary. KT77's will actually take a little higher plate voltage I believe so all should be well and good to go from 34's to KT77's.