tube question!? Myles111, out on a holiday weekend?

[Vin-erator]

I know there's a tube dude on this list. Sorry, I couldn't remember your name yesterday. Now, I know it's Myles111.

 

Can anyone tell me the difference between a 6L6, a 5881, and a KT66?

 

The 6L6 and 5881 seem virtually the same. In fact, I've seen Sovteks which say, both, 6L6 and 5881 on the tube. However, the KT66 seems very different.

 

My Marshall JTM 30 (mid to late 90's) has 5881/6L6's in it right now. Does any one know how putting in a pair of KT66 tubes might affect the performance or tone of the amp? Also, how much more space is taken up by the KT66? This JTM 30 doesn't have a lot of extra space in which to hold tubes.

 

Quite honestly, I'm looking for a way to emphasize the bass frequencies on that amp.

[BillWelcome Home Studios]

If you go to the Groove Tubes site, there is a list of tubes, by category, with a short description of each one.

 

Bill

[Dave da Dude]

Myles111 is the tube guru. There is a thread, "Ask Myles" or something like that with about 60 or 70 pages. He's the one to ask.

 

He has a great (downloadable) "Tube Primer" for a small donation.

[Werewolf by Night]

Myles is more likely to see your question if you post it right there on that "Feel free to ask Myles"-thread, too.

 

I suggest that you download his "Tube Primers" pts. 1 & 2; I think that he won't mind terribly if you can't make a donation, small or otherwise. Good info, frequently updated, too.

 

In general, the 6L6, 5881, and KT66 all have technical, internal differences, and as far as I know the first two will work in any amp that'll take 6L6s, with attention payed to bias voltage. I'm not sure off the top of my head about the KT66, in that respect.

 

Anyways, the design of the amp used has as much to do with how they may or may not sound noticeably different.

 

Some amps will place demands on the output tubes that will make the differenceses in tone more obvious, while some amps might not sound too different with any of the three.

 

Plate voltage, bias voltage, the speakers and transformers and power supply, and how you play and how hard you push the amp will all come into the equation here.

 

Also, bear in mind that there are a number of varieties of each of those three basic types, too!

[Gabriel E.]

The differences all have to do with the ratings.

 

-The 5881 (also known as the 6L6WGB) has a max plate voltage of 360v@23watts and a max screen voltage of 270v@3watts.

 

-The 6L6GC has a max plate voltage of 500v@30w and a max screen voltage of 450v@5watts.

 

-The KT-66 has a max plate voltage of 500v@25w and a max screen voltage of 400v@3.5watts.

 

There are also other 6L6-type tubes such as the 6550 (very heavy duty - max plate of 800v@42watts and max screen of 600v@8watts).

 

So if your amp can safely run 5881s (which have the lowest ratings of the three types you listed), the other tubes should work. However if it was optimized for 6550s and ran those tubes at near their maximum ratings, it would burn up a set of 6L6GCs or KT-66s.

 

The KT-66s will yeild a smoother sound with a punchy midrange. If you want to boost the bass, you might try a set of GT-6L6-GEs.

 

Specific tube data can be found here:

 

Tube Data

 

Myles' tube primer is here:

 

Tube Primer

[Vin-erator]

Originally posted by Gabriel E.:

The differences all have to do with the ratings.

Gabriel, thanks for taking the time!

 

vc

[Dave da Dude]

Originally posted by Vinny C:

Originally posted by Gabriel E.:

The differences all have to do with the ratings.

Gabriel, thanks for taking the time!

 

vc

Yeah, Gabriel too

[Gabriel E.]

Hey, no prob. It's not like I have a job or anything that I should be doing instead.

 

I forgot to mention a few things:

 

-Any time you replace power tubes, you should rebias the amp (unnecessary if the amp is cathode biased which the Marshall JTM30 isn't). This is especially true if you are switching to another kind of tube (such as from a 5881 to a 6L6GC).

 

-The ratings I listed above are simply the safe operating parameters. There are huge tonal differences between the different tube types. Tube data sheets list a bunch of other specs. and how the tubes perform in different applications.

 

-There are big differences by manufacturer and batch within the tube types and not all tubes are created equal. For this reason, it's a good idea to do your homework before investing on a set of tubes and make sure you buy from a reputable dealer.

 

-Messing with tubes and tweaking amplifiers is a black hole from which there is no return. Welcome. . .