6L6 tube types - edumacate me pls

CTN

CTN

The Drama Dude
Ok so as far as I know, there are only 3 basic 6L6 tube types/tubes that can be substituted...

5881s/6L6Gs
6L6GCs
KT66s
(am I missing any others?)

can someone educate me about the general tonal differences between them, as well as how they feel etc.

I'm thinking about getting a pair of KT66s to run my amp in 50W mode so that the current draw doesn't blow up my OT, but I don't know much about the tonal options available to me.

I've also often wondered if there's a crunchier more mid-accentuated version of a 6L6 that I could use to squeeze out a bit more of a british vibe from my amp without having to massively modify it to accomodate EL34s.
 
Re: 6L6 tube types - edumacate me pls

ConvoysToNothingness said:
Ok so as far as I know, there are only 3 basic 6L6 tube types/tubes that can be substituted...

5881s/6L6Gs
6L6GCs
KT66s
(am I missing any others?)

can someone educate me about the general tonal differences between them, as well as how they feel etc.

I'm thinking about getting a pair of KT66s to run my amp in 50W mode so that the current draw doesn't blow up my OT, but I don't know much about the tonal options available to me.

I've also often wondered if there's a crunchier more mid-accentuated version of a 6L6 that I could use to squeeze out a bit more of a british vibe from my amp without having to massively modify it to accomodate EL34s.
Click to expand...
There's always SubstiTubes / YellowJackets.

I ran EL84s in my Hot Rod DeVille and was happy.
 
Re: 6L6 tube types - edumacate me pls

I haven't really liked 6L6s in anything but old Fender designs.
 
Re: 6L6 tube types - edumacate me pls

Wait, are you saying you can run KT66's in place of 6L6's with only a rebias?

I wonder how my bassman would sound with KT66's...
 
Re: 6L6 tube types - edumacate me pls

Agileguy_101 said:
Wait, are you saying you can run KT66's in place of 6L6's with only a rebias?

I wonder how my bassman would sound with KT66's...
Click to expand...

Should but not necessarily. . If you get a set with a low draw they are ok in the old fender circuits. That being said usually the reason people dont put them in a lot of amps is they flat out wont fit. They are a much bigger bottle and alot of times you wind up hitting the head shell or something.

Keep in mind also that lots of the KT66's on the market are just re-bottled 6L6's. I have an old set of grey glass GEC KT66's and none of the new ones sound like them. Though the ones from Saratov and Shuguang will give you most of the flavor of them. The reissue Genalex and Tung-Sols sound nice but arent quite aunthentic. If your after KT66 sound I would stay away from the JJ's and the Sovteks
 
Re: 6L6 tube types - edumacate me pls

Agileguy_101 said:
Wait, are you saying you can run KT66's in place of 6L6's with only a rebias?

I wonder how my bassman would sound with KT66's...
Click to expand...

yes and no...they are pin for pin the same, but they draw a lot more current than 6L6's, and as a result, if your output transformer isn't beefy enough to handle the extra current draw, it will melt down.

I want to use only two as opposed to a full quartet so that my OT can handle the current draw. If I used 4, my OT would be getting stressed, and it's not designed for that.
 
Re: 6L6 tube types - edumacate me pls

I'll try to not get too technical with this explanation so that everyone can understand. I'll stick to comparing a 6L6 to an EL34 for simplicity; KT66s are somewhere in the middle in operational characteristics so you can extrapolate from there.

First of all, an EL34 does not produce any more midrange than a 6L6 by itself. However, the full signal characteristics of an EL34 will cause bandwidth in the OT to restrict, creating a more midrange-focused output. Full signal current of an EL34 is around 50% greater than a 6L6 in the same circuit with the appropriate screen limiting applied to both; this full signal current is what causes the pronounced midrange character of "some" EL34 amps. For this to happen, the power supply has to be appropriately sized and the OT has to be selected to begin to enter saturation at the right point. Two KT66s in a four 6L6 amp will most likely go in the opposite direction; you may lose midrange impact and the amp may sound a little sterile.

KT66s draw more heater current than 6L6s (though there are some on the market that draw about the same) which may overtax your power transformer. This would have to be compensated for with an additional filament supply. The OT doen't care; most are capable of handling significantly more power than an amp could ever output...like 2X to 4X, as long as the load is reasonable matched.

If you want more midrange focus out of your amp, your best bet would be to go to an OT with a less efficient coupling and a lower saturation threshold; you'll actually get more midrange punch than you would get from an EL34 swap.

ImmortalSix's Yellowjacket idea was a good one to consider too. They lower the plate voltage to run EL84s; lowering voltage is another way of accentuating midrange frequencies though the effect is a little different than bandwidth constriction in an OT. Bandwidth constriction causes a transition to midrange focus that is output dependent while reducing voltage creates an "always on" midrange push.

Hopefully this wasn't too wordy.
 
Re: 6L6 tube types - edumacate me pls

ConvoysToNothingness said:
Ok so as far as I know, there are only 3 basic 6L6 tube types/tubes that can be substituted...

5881s/6L6Gs
6L6GCs
KT66s
(am I missing any others?)

can someone educate me about the general tonal differences between them, as well as how they feel etc.

I'm thinking about getting a pair of KT66s to run my amp in 50W mode so that the current draw doesn't blow up my OT, but I don't know much about the tonal options available to me.

I've also often wondered if there's a crunchier more mid-accentuated version of a 6L6 that I could use to squeeze out a bit more of a british vibe from my amp without having to massively modify it to accomodate EL34s.
Click to expand...


Well, if you ever decide to modify the amp to accomodate a different pin out and heater filament requirements you might consider trying KT77s. According to what I've read (I have no real world experience) they would give you some of the mid focus normally associated with EL34s plus some 6L6ish sparkle on top.
 
Last edited:
Re: 6L6 tube types - edumacate me pls

glassman said:
I'll try to not get too technical with this explanation so that everyone can understand. I'll stick to comparing a 6L6 to an EL34 for simplicity; KT66s are somewhere in the middle in operational characteristics so you can extrapolate from there.

First of all, an EL34 does not produce any more midrange than a 6L6 by itself. However, the full signal characteristics of an EL34 will cause bandwidth in the OT to restrict, creating a more midrange-focused output. Full signal current of an EL34 is around 50% greater than a 6L6 in the same circuit with the appropriate screen limiting applied to both; this full signal current is what causes the pronounced midrange character of "some" EL34 amps. For this to happen, the power supply has to be appropriately sized and the OT has to be selected to begin to enter saturation at the right point. Two KT66s in a four 6L6 amp will most likely go in the opposite direction; you may lose midrange impact and the amp may sound a little sterile.

KT66s draw more heater current than 6L6s (though there are some on the market that draw about the same) which may overtax your power transformer. This would have to be compensated for with an additional filament supply. The OT doen't care; most are capable of handling significantly more power than an amp could ever output...like 2X to 4X, as long as the load is reasonable matched.

If you want more midrange focus out of your amp, your best bet would be to go to an OT with a less efficient coupling and a lower saturation threshold; you'll actually get more midrange punch than you would get from an EL34 swap.

ImmortalSix's Yellowjacket idea was a good one to consider too. They lower the plate voltage to run EL84s; lowering voltage is another way of accentuating midrange frequencies though the effect is a little different than bandwidth constriction in an OT. Bandwidth constriction causes a transition to midrange focus that is output dependent while reducing voltage creates an "always on" midrange push.

Hopefully this wasn't too wordy.
Click to expand...

not too wordy. I think I get what you said...sounds like a bit of a pain in the ass :(

maybe i'll just get an amp built for EL34s
 
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