Mark IV tubes – EL34/KT77?

I've been looking at these boards for awhile and there's definitely a lot of great information, so I decided to register. Hopefully you guys can help me figure this out.

I love the sound of my Mark IV short head right now with all stock 6L6s, but I've really been digging the EL34 tone lately and I understand that to get the best of both worlds I should try running a pair each of 6L6s and EL34s (inside and outside sockets respectively IIRC?). I was reading some of the descriptions of the individual tubes and retube kits on the Eurotubes site, and a friend of mine suggested the 6L6/KT77 option for me because he said the KT77s have a bit more low end than the ELs and have a really smooth, singing top end.

Have any of you tried this out, or has anyone done a comparison between EL34, E34L and KT77? My plan is to go with JJ tubes because the only other time I bought them I wasn't disappointed. I would welcome suggestions for other brands if you think they would be a better fit.

A few tones I really like are anything Petrucci, old-school Metallica, Necrophagist, Lamb of God, In Flames and Arch Enemy. I play a lot of metal but I also occasionally play some jazz and lighter rock. Is it true that Mark IV cleans suffer with a British-sounding tube?

I have tried the following: Mesa EL34, JJ EL34L, and JJ KT77. My goal was to get the best Marshall-like tone a Mark IV could get. To that end, I liked the JJ EL34L the best - it broke up early and had some balls. The Mesa EL34 broke up early but didn't have as much bass (kind of reminiscent of an actual Marshall) compared to the EL34L. The KT77 had bass, but wasn't very Marshall-like as the other two.

Having these tubes in Class A or SimulClass will rob you of your clean channel. The cleanest setup was with the KT77 in SimulClass/Pentode mode, but that's with gain very low and volume very high. So it's not as easy to achieve as having all 6L6's.

With these tubes, I thought old-school Metallica tone was somewhat doable in Pentode/SimulClass, but it wasn't as spot on as having all 6L6s - there was some flubbiness that had to be dialed out. Similarly, my recto-ish settings didn't have the chest-thumping punch it had with 6L6s.


That's my impression using a recto 2x12 (V30 + G12H).

FYI, my 6L6's include SEDs in the outer positions and JJs in the inner positions. JJs have an extended bass that's good for chest-thumping punch, so I can achieve a recto-ish tone in SimulClass/Pentode (JJs and SEDs) - comes pretty close when palm muting. For old-school Metallica, it seems easiest to achieve using only the SEDs (Class A).

Ultimately, I reverted to the all 6L6s configuration since I already have a Marshall and I know how to work the Mark IV better in this configuration.

Hope that helps.