Tube of the Month : The SPHERIA

Hi!

In the last post about the European Triode Festival, I showed a photo of the two very old directly heated triodes which I bought at the auction in Denmark. After returning from the ETF I tried to gather some information about them and it turns out that these are very interesting tubes and very little is known about them. So let me share the little information I have about the Spheria.

What a cool name, no? The name seems totally out of time for a tube which was manufactured about 90 years ago. Could be a name for a product of our time.

The Spheria is a small directly heated triode. It has a European 4 Pin base. The base connections are shown at the left. This base was the european counterpart of the american UX4. All information I found indicated that it is an equivalent or very similar to the Telefunken RE074 or Philips Miniwatt A409. These have a filament voltage of 4 at a very low current of only 60mA. If the tube is similar to those it should have a mu of about 10 with a plate resistance of 10k which would mean a transconductance of 1mS (1000 micromohs). So I measured those values to see if they are really the same. I started with a low filament voltage of 3V and the power supply set to current limiting. Then increased the voltage until I reached 50mA. The plate curves would saturate quite early with filament voltages below 3.5V. At 3.8V they start to look good. and the filament current settled at 60mA. The 4V/60mA filament spec seems to be correct. The the other values however are quite different from the RE074 and A409. I measured an amplification factor very close to 7 coupled with a plate resistance of 15kOhms and about 0.5mS transconductance. These values turn out to be very close to those of the Philips A406. Below the set of plate curves which I generated:

Nicely linear curves as expected from a directly heated triode! Now let's have a look at some photo shots of this beauty:

Isn't that gorgeous?

All information I could find about the origins of these tubes was that they were made in Belgium in the 1920ies. I talked to many old tube heads and most never even heard of the Spheria.

No markings of manufacturer or information about the country of origin can be found on the tubes.

And they came without any packaging which probably disintegrated decades ago.

After some digging around and talking to people I assume that the tube was probably made in a small batch and was most likely a custom development for a specific application.

The manufacturer was most likely the company M.B.L.E. in Belgium which started as a light bulb company and later produced tubes under the Mazda and Adzam brands.

Let's try to get a glimpse of the internal structure.

Since the top is mostly covered with getter material, the internals can only be seen when looking into the tube from the base side

As in many other early triodes the internals are mounted horizontally rather than vertically as in more modern tubes.

The plate is cylindrical and the grid is a nicely wound spiral inside

The filament consists of a single very thin wire which is connected and supported at both sides. Theoretically the perfect arrangement. Let's see how the tube looks with the filament lit up.

As can be seen it has a tungsten filament which is most likely thoriated.

View from the side:

Close ups:

Some more photos:

What a great little tube and marvellous piece of early vacuum tube engineering. If anybody has more information about this tube and it's history please contact me and I will share it. Also if anybody has some of these to sell or swap, let me know. I will see what I can build with them, maybe for next years ETF.

Best regards

Thomas

P.S.: A reader of my blog provided a link with some information about the Spheria. It was used in a radio made by the french manufacturer Gerard Pericaud.

European Triode Festival, ETF 2015 - recap

Hi!

After arriving back home and recovering from the 3 intense days and long drive, I went through all the photos again. When I do the 'live' reports there is not much time to screen all photos, some good ones had been left out. This is a good opportunity to write one more post about the ETF.

The system which was built up for the shootout deserves a few more words. Due to the use of the huge baffle it was named the Wall of Sound which reminded about the wall of sound speaker we had at the ETFs in Langenargen in 2004 and 2005.

Unfortunately I do not have any technical information about the drivers used. The horns showed some incredible craftsmanship. 

The sound of the system was quite well balanced and refined with nice reproduction of tone colours. The Danish team did an incredible job with building this system which was capable to fill such a huge room with sound and able to make the small differences audible.

During the first shootout day a Berning amp was used  which had a slight tendency to harsh sound. During the finals the amp got swapped to a DIY one which sounded much smoother and better. The shootout was very interesting. During some rounds the differences were quite audible. As you can see here, during this round Julien was confident that he picked the right one:

While Jerome was still wondering which one to prefer:

This shootout was well prepared and handled. Again congratulation to Bjorn and Karsten for the great job. Since I was involved in a shootout preparation once I know how much work this is.

Another point I did not cover yet is the lectures. The programme is filled with lectures about various topics. People are free to attend these or not. I usually took the time during the lectures to go through the rooms and take some photos. So I must admit I missed them. But I still would like to thank all those who spent the time to prepare a lecture and share their knowledge with the audience.

The amount of knowledge and experience in different fields which is present at the ETF is remarkable and the willingness to share is what contributes a lot to the spirit of the ETF. There is Stephan Götze for example who brings stacks of equipment every year:

And he does it so that anybody can come to him with his amp or preamp and have it measured or troubleshooted  if it is not working as it should. Stephan is very helpful and good in finding the issues. Of course he also brings some of his own creations. Check out this tonearm:

There is also never a shortage of tube testers at the ETF. Just in case someone needs some tubes tested:

It is also very common that people bring uncompleted projects on which they are working to the festival and continue to finish them during those days. Here for example a line stage which was built by Claus based on a kit from me:

He got it working during the time at Sankt Helene!

Adrianus brought this beautiful Edison Phonograph:

And of course there is the endless amounts of amplifiers. It is amazing to see all these different styles and ideas.

Here a guy from Norway reused the chassis of an old Oscilloscope for his amp:

I was told that this amp came to life for the first time during the ETF:

People are never shy to show the inside of their work:

Although it is called Triode Festival, transistor amps are allowed too. I spotted this Classe Audio amp:

Especially remarkable is the creativity. For example this DAC:

Oliver modified his amp which I pictured last year already. He now uses 809 output tubes.

He kept the beautiful 816 rectifiers.

Can't get enough of the blue glow!

The proud owner:

As we get older, the weight of the amps becomes more and more of an issue. That's why some people start to use switched mode power supplies as seen here in a 845 amp by Benny Glass:

Sometimes it is the small and humble systems which are the most surprising. I already posted a video about a system with small speakers using Foster drivers.

Since the topic of the shootout was power supplies, There was an abundance of voltage stabiliser tubes.

Many beautiful turntables. Among them this creation from Frank Schröder:

And of course tubes, tubes and more tubes:

When these two beauties were offered at the auction, I had to get them:

Directly heated triodes called 'Spheria'. Made in Belgium about 90 years ago. I will test them and write more in an upcoming post. Might build something with them for next years ETF.

I'd like to thank the organisers for this wonderful festival and for carrying on the tradition!

Best regards

Thomas