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Anyone have any experience with putting 6L6's in a Marshall.

I am wondering how they changed the sound.

Well Marshall installed 5881's in their amps from the mid through the late 90's. Those are essentially 6L6 type tubes. They install 6L6/5881's in JTM45's and Blues Breaker combo's and that does produce a more Fendery tone, but it's still not a Fender tone, it's still a Marshall. The original Marshall sound was built around the KT66 tube, and they were like a super duty ballsier 6L6. Hendrix at Monterey and early Cream are good examples of KT66 Marshall tone.

I have installed 6L6's into a Jubilee amp and it sounded great, but the tubes were running fairly hot. 6L6's require more bias voltage than EL34's, so it would have required major changes to the bias circut for a permament swap. I just went back to EL34's. Amps wired for EL34's can take 6L6's no problem, provided they can be biased. However, Amps exclusively wired for 6L6 tubes may require rewiring of the sockets to accept EL34's.

the funny thing is that a tech here put 6L6's in my sold JTM60 once and i didnt know it. when i got it back i was like wow! it sounded that much better.
makes me laugh now cause techs here in Greece ( it was the authorized Marshall dealer!) just do whatever.

anyway, it sounded waaaay better and i didnt know what the heck was up with it.

try it out

The old SuperLeads had 6CA7's, they had that rounder bottom than the EL-34's.
Very American sounding in some respects.

Great input guys.

I was thinking more aloing the lines of taming those spikey Marshall's.

IE: I am wondering what one of my 4203's would sound like with 6L6's.

It just seems that it could create an interesting change to a Marshall.


Originally Posted by RidThe old SuperLeads had 6CA7's, they had that rounder bottom than the EL-34's.
Very American sounding in some respects.

1. They add a fair bit of 6L6-ish-ness and are electrically equivalent to EL34s.

Yeah had a funny blend of British and US
Very nice indeed.

It works out really well. Go out and try a tweed Bassman.

KT66'd have balls and a nice top on the crunch. I like 5881's, give you clarity, controllable mids, and GLASS on the top and upper mids.

I am an El34 guy myself though.

i run kt66's in my 4210 and it sounds amazing, loud as hell and biased way hot, but sounds great

I heard once that Jeff and Kerry from Slayer run 6L6's in their Marshalls. Is this true?

Can KT66s go in a 6L6 amp without rewiring the tube sockets? How does their sound vary from a 6L6?

Tubes are beautiful... Music's equivalent of beer. Lots of flavors, but they all taste good.


Originally Posted by Nite_Maresz_25I heard once that Jeff and Kerry from Slayer run 6L6's in their Marshalls. Is this true?i think they use 6550's

Well, I've got a JCM800 lead combo, i once mentioned in my earlier threads. I said that the amp uses 6L6 tubes and I can't remember who(sorry mate), told me to trash those and replace them with EL34s, which is suppose to give the classic Marshall tone. Well, i don't know if the amp is bias or re-wired to make compatible with 6L6s. But whatever the amp comes with it, I just play safe to stick to what it has until it tubes blows and I get the tech to check it out for me. =)

P.S the amps i've got are pre-owned


Originally Posted by n00bCan KT66s go in a 6L6 amp without rewiring the tube sockets? How does their sound vary from a 6L6?

Yes, they can. KT66's have a more stout and barrel-chested midrange which is almost walnutty, they transition into overdrive more gradually than a 6L6 (somewhat like an EL34). KT66's have tighter low end and more headroom than an EL34...and IIRC they have a bit crisper top end than the EL34 but it's been a while since I had KT66's in amps I use regularly. Overall I would say the KT66 is somewhere between the 6L6 and the EL34....oh, and they're hoppy.


Originally Posted by chillYes, they can. KT66's have a more stout and barrel-chested midrange which is almost walnutty, they transition into overdrive more gradually than a 6L6 (somewhat like an EL34). KT66's have tighter low end and more headroom than an EL34...and IIRC they have a bit crisper top end than the EL34 but it's been a while since I had KT66's in amps I use regularly. Overall I would say the KT66 is somewhere between the 6L6 and the EL34....oh, and they're hoppy.

Thanks for the description. quot;somewhere between the 6L6 and the EL34quot; is exactly what I'm looking for. How do KT66s compare to 5881s (which is more in the direction of an EL34)?

5881's will distort more quickly. But, 5881's are pretty hoppy as well, with a twist of lemon.

One of the things you can do with a master volume JCM 800 Marshall is to have your tech clip out the capacitor on the gain pot--this acts like a quot;britequot; switch at lower gain levels. Without this cap the tone is more consistent over the range of input gain.

Marshalls are really easy to figure out. They sound like caa-caa at practice volumes. Crank them up on a stage with a 412 and get them nice and hot--by about that third set--all that shrillness is GONE. The 412 moves enough air to make your low notes SOLID, the midrange crunchy, and the trebles sing ever so sweetly.

I had a JCM 800 4010 50-watt 112 combo that sucked as a practice amp. But the few gigs that I did with that little monster cranked up were most satisfying. It would really sing.

I don't think I would waste a lot of time and money re-tubing and modding a Marshall with 6L6s. (Taking a 6550 Marshall and setting it up for EL34s though, probably is a worthwhile endeavor.) There are just too many good 6L6 amps out there to bother with this, IMHO.

I would suggest finding a Mark III Simul-Class Boogie (or even a Mark IV), and run it with a combination of 6L6s in the Class AB sockets, and EL34s in the Class A Simu-Class sockets. This gives a nice mix of 6L6 quot;bottom-end thumpquot; and quot;top-end airquot;, with the EL-34 quot;mid-range aggressionquot;. That may give you the quot;meldedquot; tone you're looking for. It's just one of many options.

Good Luck.

Bill