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Wednesday, October 21, 2020

The Trinity of ELROG 300B Tubes


In August I published a post about the 4th anniversary of Deutsche Elektronenröhren Manufaktur GmbH in which I showed the new molybdenum version of our 300B, the ER300B-Mo. The development did not end there and our 300B line up is now joined by a third model.

Regular readers of my blog know how fond I am of the 46 tube. Unfortunately this tube delivers just up to 1.25W in single ended operation or a bit over 3W in a push pull configuration which severely limits the choice of speakers to go with that tube. So rather than merely developing an ELROG ER46 we decided to attempt to recreate the sound of the 46 in a tube which can deliver more power.

I am proud to announce that we not only achieved to recreate the special sound of the 46 in a 300B compatible tube, but in my humble opinion even surpassed it by adding the neutrality and resolution which our thoriated tungsten 300Bs are known for.

This perfectly suits my own preference for sound. Musical flow, voices and tone with a lot of emotional impact combined with the highest possible resolution and neutrality. Hence the tube received my initials in the type number and is called the ELROG TM300B.

We went through quite a few prototypes with a new filament and grid structure which is very difficult to manufacture. Therefore we can only produce very limited numbers of this tube. Initially it will be reserved to users of Thomas Mayer amplifiers only. But a general release for use in other amplifiers is panned for later next year.

The molybdenum plate ER300B-Mo is released without restrictions and can be ordered now.

But we still have a bit of lead time since the pre orders of the ER300B-Mo will be served first.

We already received some feedback about the sound quality of this tube and general consensus is that it improves upon the qualities of the standard ER300B.

Here a feedback from an early user of this tube:

To me the sound of the ER 300B M are again more gripping. More linear. More solid, locked imaging. Better dynamics. More separation. 
 It feels like the ’transport’ of the sound is more rock solid. It really feels like the same kinda musical step up i experienced going from the my previous set of tubes to the normal ER300B’s. 
But now it’s an even more ’solid’ version. The sound signature is the same as the standard ER300B, but everything is much better. 
I was listening at the new Tool album, from which is not easy to uncover all the details. It can actually sound very flat on a normal system. With the ER300B M, I finally hear way more separation of frequencies, and as a result it sounds way more ‘grunting’ and ‘gripping’. 

Another customer feedback:

They sound spectacular: more of everything, micro detail shimmer on cymbals, bite on trumpets, more nuanced soundstage, bass seems tighten and more defined as well.

I can confirm similar findings in my amplifiers. It is not a subtle difference but immediately noticeable. Of course these new tubes do not render the standard ER300B obsolete. It sill be continued to be offered along these new versions.

We did a minor change in the ER300B. We switched to a different supplier for the nickel used in the plates. The plates are thicker and have better thermal properties. This enabled us to leave out the black coating which we used to apply to the plates. So the plates are shiny now. In terms of performance and sound we did not see any change in this so it is purely cosmetic.

With the addition of the TM300B the ELROG portfolio consists of 13 tube types now. And we are able to offer a choice of different types to 300B users.

Pricing of the ER300B-Mo and our other models can found on the tube site. The ER300B-Mo has the same technical parameters as the ER300B and is also warranted for 1 year.

Best regards


Monday, October 12, 2020

Tube of the Month : The 6N7 (revisited)


Since I just showed a set of 2A3 amplifiers which use the 6N7 as driver I thought it is a good idea to have a look at this tube again in detail.

The 6N7 was one of the first tubes which I presented and was shown in the Tube of the Month post in February 2011. But that was a rather short post with only a few photos. So let's have a look at it again.

The 6N7 is a double triode. Both triodes have the cathodes internally connected. The tube was designed with two applications in mind. One of them a Class B output stage and the other as Class A driver with both halves connected in parallel. The latter is the way I am using this tube to drive small output tubes like the 45, 46, 2A3 and also the 6CB5A. The 6N7 has an octal base. The pinout can be seen on the left. With both triodes in parallel it has a plate resistance of 10 kOhm which is just low enough to use it with interstage transformers. It can also be used with inductive or restive load of course. Due to the highish plate resistance a high quality interstage transformer is needed with sufficient primary inductance to allow good frequency response. The tube uses a 6,3V heater which needs 0.8A. The amplification factor is 35 which is a good value to be able to build 2 stage amplifiers with the aforementioned output tubes and still have a good input sensitivity. For the complete technical details refer to the General Electric data sheet. The 6N7 was made in both ST shoulder type glass (6N7G) and also tubular straight sided glass (6N7GT) as well as with metal shell (6N7). Before we look at the various tubes, let's examine the linearity of the tube in Class A mode. Here the curve set from the data sheet:

And here the plate curves taken with the tracer with both halves wired in parallel:

Since I use the 6N7 a lot I have a big stash from different manufacturers.

A 6N7G made by RCA.

A lot of getter in this one.

This tube came in a nice box with the RCA 'meatball' logo.

Sealed boxes:

This type of packaging is the only way to be sure the tube is NOS and not used. The tubes can be tested in box without tearing the carton.

Another one:


More variations:

JAN CRC 6N7GT made by RCA for the military:

The glass of this one has a grey coating.

Another one with coated glass but in commercial packaging:

A metal 6N7 by RCA:

6N7 made for the military:

The box on the right says Canadian Armed Services but looks like RCA made.

Sylvania 6N7G:

Sylvania 6N7GT:

Metal 6N7 made by Sylvania:

National Union 6N7G and 6N7:


Part of the glass is blacked.

Metal 6N7 by Ken-Rad:

Philco 6N7G:

Various glass and metal 6N7 made by Raytheon:

The next two are rebranded 6N7GT:

This metal 6N7 came in an International Service Master box (a parts supplier) and has no markings on the tube:


Visseux 6N7GT made in France:

Tung-Sol 6N7GT with blacked glass:

This 6N7GT has one side with open heater, so a good candidate to open up:

One of the two triodes:

Cathode and grid:

The heater:


Best regards