KT66 vs 6v6

[dragonbat13]

What similarities or differences do these tubes have other than output power?

[thetragichero]

might you mean kt66 and 6L6?

[Willabe]

A lot, they sound nothing like each other.

A 6L6GB/GC would sound closer to a 6V6 than a KT66 and 6L6GB/GC's don't sound that close to a 6V6. Just like an EL84 doesn't sound that similar to an EL34. Yes, an EL84 will sound closer to an EL34 than a 6V6 or 6L6GB/GC, but they do sound different.

Bigger tubes typically sound fuller, have more bottom end than smaller tubes. But part of that is they are used in louder amps and to your ear, that effects what your hearing.     

KT66 will have a bigger fuller bottom end than a 6V6. But again part of that is their used in louder amps and it effects your ears differently.

[Willabe]

They say John Mayalls Blues Breakers ('Beano') album with Clapton on guitar was recorded with Clapton playing through a Marshall combo amp with KT66's in it.

That amp, dubbed the Blues Breaker amp years later, was an old Marshall that was still closer to a Fender tweed Bassman than later Marshall amps.

That albums on youtube, listen to it. Clapton does have it turned up, so it's distorting.

KT66's would sound different than 6L6GB/GC's in a black face amp. Probably a little bigger/fuller bottom and a little rougher, little more/different distortion. But KT66's in a BF Fender wouldn't make it sound like a Marshall. 

Power tubes do break up a little different from each other.

6L6's, 6V6's are beam pentodes, they have 2 grids and have beam forming plates instead of a true 3rd grid, suppressor grid, EL34, EL84's are true pentodes, with 3 true grids, and KT66, KT77, KT88's are tetrodes with only 2 grids, no suppressor/beam forming plates, so they sound a little different from each other.

The grids, or lack of a grid and beam forming plates change the tubes internal capacitance's, gm (transconductance) and it's plates internal resistance and that effects the tubes sound/output.     

[jordan86]

Not many similarities. Ive always understood the KT66 to be the British equivalent to the 6L6. Or maybe better said...it’s a decidedly British sounding tube, but the most 6L6 like of the British big bottle family. It’s warmer and more open than an EL34. Less compressed. 6V6’s are more American voiced (although a little more mid forward) and generally a smaller sounding tube. Both can be pretty “warm”. I guess that would be one of the few similarities.

[tubenit]

6L6 vs. KT66

[DougGuy]

I have a JTM45 clone with KT66 and a JMP 50w clone with EL34s and the KT66 amp is very different sounding, it's crisper, the bottom is stout and not very distorted, mids are growly and the highs are screaming.

In a tweed amp, I am told the 66s are very Stones-ish sounding.  I want to convert my 5g9 Tremolux from 6v6 to KT66 at some point.  The biggest requirement afaik is the heater amps, the 5g9 would need 5a of 6.3v current so a PT that has that much current on the 6.3v tap would be required.  I would also add more filtering.  If the KT66 in a tweed platform shares ANY of the similarities of the KT66 in a JTM format, it would be a very worthwhile upgrade.

After watching the video, that is a pretty off base comparison of the two tubes, that guy makes them sound pretty much the same with tiny differences.  I run KT66 and EL34 into a Marshall 4x12 with JBLs wired in stereo, the JTM with KT66 gets one pair, the JMP 50w gets the other pair and they have very noticeable differences right away.  In my setting, the KT66 are well defined, solos just sing and multiple note bends seem to highlight the clashing harmonies and dissonant intervals behind the primary notes.  Very textured and dimensional moreso than the EL34.

I would love to hear the comparisons in a tweed amp.

[pdf64]

…KT66 … are tetrodes with only 2 grids, no suppressor/beam forming plates, …

KT66 are beam power valves, described in the 60s as beam pentodes, later marketed as beam tetrodes.
https://frank.pocnet.net/sheets/126/k/KT66.pdf

https://frank.pocnet.net/sheets/086/k/KT66.pdf

My view is that it seems sensible to think of beam type valves as pentodes, as there are 5 electrodes, and the beam forming plates undertake the same function as the suppressor grid in the Phillips patented pentode.

I think it reasonable to put them in the 6L6 type family, ie very similar characteristics but they need a bit more bias voltage.

If the KT66 in a tweed platform shares ANY of the similarities of the KT66 in a JTM format

I don’t see the distinction being made between early Marshalls and Tweed amps? At least in regard of the circuit. Main differences look to be in the chassis layout.

[Willabe]

I always thought they were tetrodes because KT stands for 'Kinkless Tetrode'.

Wonder why they went with KT? 

[mresistor]

Wow this is cool..  Yesterday I was reading Blind Lemons thread about a small lightweight amp with more headroom, and the subject came up about an AA964 princeton and I got to thinking since he was talking about using a larger PT for more oomph..  why not use KT66's in it.   That would be a little monster.  Also a 5E9-A would be cool with KT66's.

[66Strat]

KT66s are big tubes. Chassis layout could be problematic if adequate spacing is not provided between tubes. GEC recommends a minimum of 3.5 inches (9 cm) on center if operated at maximum ratings. GEC also recommends 10K to 50K grid stoppers to prevent parasitic oscillations. See pages 4 and 5 in the attached.

[PRR]

I always thought they were tetrodes because KT stands for 'Kinkless Tetrode'.
Wonder why they went with KT? 

Patent issues. Philips patented the Power Pentode. This is a key reason RCA worked with Critical Distance theory which gives a G2 effect without a grid in the electron path.

It's all 1930s BS. All these patents, even the last ones, were cross-licensed by 1950s and expired soon after. Also we know that some of these tubes exist made both ways.

Technical marketing is always dubious. Watt criticized Stevenson for using dangerous "High Pressure" steam, and he knew better, but he was losing market share.

[pdf64]

Here’s some further background http://www.r-type.org/static/grid14.htm

[Willabe]

I have a JTM45 clone with KT66 and a JMP 50w clone with EL34s and the KT66 amp is very different sounding, it's crisper, the bottom is stout and not very distorted, mids are growly and the highs are screaming.

What happens when you put the KT66's in the JMP50 clone and the EL34's in the JTM45?

After watching the video, that is a pretty off base comparison of the two tubes, that guy makes them sound pretty much the same with tiny differences.  I run KT66 and EL34 into a Marshall 4x12 with JBLs wired in stereo, the JTM with KT66 gets one pair, the JMP 50w gets the other pair and they have very noticeable differences right away.  In my setting, the KT66 are well defined, solos just sing and multiple note bends seem to highlight the clashing harmonies and dissonant intervals behind the primary notes.  Very textured and dimensional moreso than the EL34.

Not sure that was a fair comparison he did? He said with both tube sets he had the bass control set completely off. And the 6L6's were old, tubes lose top end after breaking in some. And who knows where the bias was set for either set of tubes? 

[DougGuy]

I have a JTM45 clone with KT66 and a JMP 50w clone with EL34s and the KT66 amp is very different sounding, it's crisper, the bottom is stout and not very distorted, mids are growly and the highs are screaming.

What happens when you put the KT66's in the JMP50 clone and the EL34's in the JTM45?

I don't know, never swapped them around.  The JTM sounds like Joe Perry.

After watching the video, that is a pretty off base comparison of the two tubes, that guy makes them sound pretty much the same with tiny differences.  I run KT66 and EL34 into a Marshall 4x12 with JBLs wired in stereo, the JTM with KT66 gets one pair, the JMP 50w gets the other pair and they have very noticeable differences right away.  In my setting, the KT66 are well defined, solos just sing and multiple note bends seem to highlight the clashing harmonies and dissonant intervals behind the primary notes.  Very textured and dimensional moreso than the EL34.

Not sure that was a fair comparison he did? He said with both tube sets he had the bass control set completely off. And the 6L6's were old, tubes lose top end after breaking in some. And who knows where the bias was set for either set of tubes? 

Never tried an A/B in the same amp, so I guess my comparisons unfairly give the KT66 and edge but between my two amps I described, the difference is not very subtle at all. 

Once I get the 5g9 sorted and get ready to swap the tubes I can do a 6v6 sound clip and then a KT66 sound clip once the change is done.  I think that would be an acceptable test for 6v6 vs. KT66.

[PharmRock]

I built a Trinity Triwatt kit a year or so ago.  This amp is a lower wattage Hiwatt clone that can run either 2xKT66 or 2x6V6, fixed bias.  Change tubes, flip a switch to change the bias range resistor, and do a quick bias and you are all set.  There was a noticeable difference between the two.  The KT66's had a very full round low end and glassy top end.  3-dimensional sounding.  Same amp settings with the 6V6 was a little fatter in the midrange and a little hairier.  Night and day difference.  Even with the master volume cranked, the KT66's were pretty clean and "pure" sounding.  A lot of this has to do with the Hiwatt circuit but when 6V6's were used it was definitely a different sound. 

I also built a Trinity Tramp a while back, which is based on a Champ but on steroids.  This amp had switchable OT primaries as well as switchable cathode resistors, so you can run pretty much any octal tube as long as it would clear the speaker magnet in the cab.  Again, the KT66 was very 'pristine" sounding...clear highs and very full and articulate lows.  The 6V6 resulted in what one would typically think it would...fatter and overdriven. 

I am building a JTM45 at the moment and from all the clips I've listened to comparing KT66 to EL34,  I've decided to go with KT66's.  Just a great sounding tube. 

[Willabe]

Even with the master volume cranked, the KT66's were pretty clean and "pure" sounding.

Which brand of KT66's?

[Willabe]

I have a JTM45 clone with KT66......

Which brand of KT66's?

[PharmRock]

Even with the master volume cranked, the KT66's were pretty clean and "pure" sounding.

Which brand of KT66's?

New production Gold Lion

[pdf64]

What similarities or differences do these tubes have other than output power?

Do you mean to compare KT66 to 6V6, or to 6L6?

[DougGuy]

I have a JTM45 clone with KT66......

Which brand of KT66's?

New Production Golden Lion

The KT66's had a very full round low end and glassy top end.  3-dimensional sounding.  Same amp settings with the 6V6 was a little fatter in the midrange and a little hairier.  Night and day difference.  Even with the master volume cranked, the KT66's were pretty clean and "pure" sounding. 

This pretty much describes how the KT66 sound in my JTM clone also.  When Pharm says "pure" think pure tube tone, Joe Perry plays these clean and hard, and even with a klon pedal you still hear the unique tubiness that is the KT66' tonal signature.  Now, we are getting into an area totally devoid of bias and plate current, we are getting into the AUDIO flavors of tube vs/ tube.  What does it do to the ears, the tone of the guitar(s) the frequency response in a totally musical term, different from anything you would see on an O scope. 

I think there should be two completely separate and unrelated schools of discussion when it comes to tube comparisons in guitar amps, since one doesn't begin to explain the other one and vice versa. 

The *sound* of the KT66? Pharm nailed it.  I suspect his comparison to the 6v6 in the amps he used to pretty much parallel mine, when I get around to doing it.

[HotBluePlates]

I always thought they were tetrodes because KT stands for 'Kinkless Tetrode'.

Wonder why they went with KT? 

PRR already explained it, but the KT-tubes are tetrodes in the same way that 6L6s & 6V6s are tetrodes (even though those were called "beam power tubes" for the longest time).  They're all using beam-forming plates (and specific spacing between screen & plate) to avoid the need for a suppressor grid.

... Also we know that some of these tubes exist made both ways. ...

RCA's 6BQ5 data sheet says the tube is a "power pentode."  But looking at the fine details of a large number of RCA 6BQ5s & 7189s, some have a suppressor grid visible through a gap in the plate, while others have obvious beam-forming plates.  And this variation during what must have been approximately the same time period (both types were black plate tubes with otherwise similar details).

Maybe different RCA factories had one line set up for beam power tubes, a different factory line set up for pentodes.

[PRR]

> RCA's 6BQ5

RCA made a LOT of Mediterranean-styled faux-Cherry/Walnut AM *and* FM *and* recordchanger livingroom consoles. (Probably still made in the old Victrola woodshop.) Nobody really cared if those bottles had a wound G3 or metal-stampings.

[svejkist]

I always thought they were tetrodes because KT stands for 'Kinkless Tetrode'.

Wonder why they went with KT? 

I can't confirm that they chose the KT nomenclature to stand for kinkless tetrode, but a kinkless tetrode and a beam pentode are the same thing, so it is certainly plausible. True tetrodes, with no beam forming plate, have a "kink" in their plate current curve at low plate voltages, due to secondary emissions from the plate collecting on the screen grid. Beam forming plates, like suppressor grids on pentodes, eliminate (or at least greatly mitigate) this kink. So yes, a KT66 is a kinkless tetrode, beam tetrode, beam pentode, and whatever else the marketer is calling that design these days. As pdf said, they were designed to function like pentodes, without infringing on the pentode patent. Hence the confusing array of descriptions.

[PRR]

Beam Pentode? Where did you find that?

They were always called "tetrode" to evade the power pentode patent.

[pdf64]

Marconi initially referred to the KT66 as an ‘output tetrode’.

https://frank.pocnet.net/sheets/179/k/KT66.pdf

But by the 50s were using the term ‘beam pentode’.

https://frank.pocnet.net/sheets/126/k/KT66.pdf

I think it may only have been RCA not to use the ‘beam pentode’ terminology, preferring ‘beam power’.

https://tubedata.altanatubes.com.br/sheets/021/6/6L6.pdf

Other manufacturers were using the term ‘beam pentode’ by the early 50s.
https://tubedata.altanatubes.com.br/sheets/127/6/6L6G.pdf

[svejkist]

Beam Pentode? Where did you find that?

They were always called "tetrode" to evade the power pentode patent.

Well, one place I heard it was in this thread. I added that terminology because that is what Willabe called them in the post that prompted the question I was responding too. Another place would be this GE 6V6 datasheet.

https://frank.pocnet.net/sheets/093/6/6V6GT.pdf

Patents run out, and at any rate only restrict the manufacturer. That said, IANAL, but I am positive the patent would not cover the name. That would have to be trademarked.

[PRR]

I apologize for my error.