DISCLAIMER

DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

All rights of photos and text reserved. Usage of photos or text from my blog on other websites or for any other purpose only with prior permission. If you want to use any material from my blog please contact me by email.



Friday, October 31, 2014

ELROG ER300B production tubes start to roll in

Hi!

The first tubes from series production start to come in. I expect shipments of just a few pairs each week during the next month. Since there is already a considerable queue of pre orders, I am not taking any more orders until most of the already pre ordered tubes are delivered.




Further impressions of the tubes will be published soon when I also get some feedback from other listeners. Stay tuned.

Best regards

Thomas

Monday, October 27, 2014

Tube of the Month : The 6GE5

Hi!

Most of you probably expected the 300B to be this months tube. But after all the attention it got on my blog recently, I decided to set a counterpoint by selecting a totally different tube for October. A Compactron Beam Power Pentode, the 6GE5.




As fond as I am of directly heated triodes, I also like to work with 'sleepers'. These are tubes which are largely ignored by tube amplifier builders but which are very usable in audio applications. One of them is the 6CB5A, also a beam power pentode. Many years ago I proposed the use of triode strapped 6CB5As as low cost 300B alternative. Quite a few 6CB5A amps have been built around the globe since then.

In the 1960ies General Electric introduced the compactron tubes with 12 pin bases. This class of tubes was intended to rival the transistor which started to replace vacuum tubes. With the 12 pins more systems could be integrated into a single bulb. There have been triple triodes, quad diodes, twin pentodes and many combinations. The 6GE5 is a single beam power pentode, thus it does not need all the 12 pins. Yet many such types with single systems have also been put on 12 pin compactron bases to enable TV sets which only need a single type of socket. I already covered some 12 pin compactron types, the 6U10, 6HS5, 6HV5A and 6CG3. There are many more hidden gems in this series of tubes and I intend to present some of them during the next year.
So why the 6GE5? With the 6CB5A there is already a good alternative for the 300B so maybe something smaller would be nice. Also many people don't like tubes with top caps, so I picked one without. The 6GE5 was intended as horizontal deflection amplifier tube in TV sets, a so called 'sweep tube'. It has a lower plate dissipation than the 6CB5A, only 17.5W which also comes with a lower heater current of 1.2A, less than half that of the 6CB5A. The 6GE5 data sheet lists the triode amplification factor as 4.4. Plate dissipation and amplification factor are remarkably close to the 2A3, so maybe the 6GE5 could turn out to be a nice low cost alternative to the 2A3 and get us some 3.5W in single ended configuration? To find this out we need to get the values for plate resistance, transconductance in triode mode and of course we need to see the plate curves. The data sheet does not show the triode curves, so I measured them with a curve tracer:




This is about as good as you can expect from an indirectly heated tube. Quite good linearity in the mid range with the spacings of the pate curves getting a bit larger between the 0V and 10V grid step. How about the transconductance? This can be derived from the plate curves, but I took the easy way and just measured it on the tube tester. With 300V on the plate and 55mA current I got 5300 micromohs (5.3mS) almost identical to the 2A3s 5250. The plate resistance is easily calculated as amplification factor divided by transconductance which gives 830 Ohms. Again close to the 2A3s 800.

Before we go more into detail about the use of the 6GE3 in a single ended amplifier, lets have a closer look at the tube. So far I only have 2 of them so I cannot show many photos of different brands. The ones I have are Made by General Electric:





The 6GE5 has a nice shape with it's rather short but and bottle.





A view from the top showing the grid cooling fin:





Let's open one of them to see how they are constructed inside:





The top, the heater is visible inside the cathode:




The bottom:




Removing the heater:




The heater wire:



A close up:




The beam plate with the cathode still inside, the grids are already removed:




This photo shows how the beam plate is internally connected to the cathode:




A close up of the cathode:




The beam forming plate:




All the electrodes side by side, heater, cathode, control grid, screen grid, beam plate and plate:




The grids:




The control grid is gold plated and the screen grid has some kind of carbon treatment to increase it's dissipation capability. A close up of the grids:




Another view of the control grid:




So how to use this tube in a single ended audio amp? From the values discussed above it is quite obvious that the tube could be used with typical 2A3 operating points. But maybe this can be optimised a bit. I used the set of plate curves from the curve tracer and extrapolated some additional grid lines since the tracer only works up to 400V :




Operation into a 5kOhm load is represented by the blue line. I would pick 300V on the plate and 55mA as operating point. The bias voltage on the grid is -55V which is convenient since it can be obtained with a 1kOhm cathode resistor. The B+ voltage would then have to be set to about 350V. It would be 355V to be exact but no need to be picky. A solid 4W should be obtainable like this.

Expect more about this tube on my blog soon. After selection of a suitable driver tube from the 12-pin compactron series, I will build a prototype amp. Stay tuned!

Best regards

Thomas






Thursday, October 23, 2014

ETF.14 Berlin November 20 - 23

Hi!

This years ETF is coming up. As last year I will post reports and keep you updated about the highlights of the event. I will also show some stuff myself,a new version of the ShellacSavor preamp with variable EQ settings for 78rpm records.





This preamp will be part of a joint set up with my friend Frank, who introduced me to 78rpm records after last years ETF. Frank prepared a presentation and will talk about the history of Shellac records and we will demo with a broad selection of Jazz music.


Different to the first implementation, the new preamp comes with a separate power supply to minimise PSU interference.




Besides this I will also bring a D3a LCR phono stage, the 'phase 1' cost down version. It will be combined with a matching line stage, the 6AH4 preamplifier. These units will be part of the system of the Munich gang.

Tune in November 20th through 23rd for 'almost live' updates from the ETF!

Best regards

Thomas

Thursday, October 16, 2014

ELROG ER-300B, First Impressions

Hi!

After having the tubes for about a week now and after various listening sessions and measurements, I am ready to share my first impressions.




As was expected, Elrog would not just merely try to copy the Western Electric 300B. There are already various 300Bs on the market trying to achieve that. Some of them actually not bad at all. So the intention was to create something which has the potential to be better and yet compatible with existing 300B amplifiers.

When I had my initial discussion about a 300B with Dr. Schaffernicht during my visit in 2013, I mentioned that a 300B with thoriated tungsten filaments would be something really new and cool. People who follow my blog probably noticed my preference for these bright filament tubes. Dr. Schaffernicht liked this idea a lot, since he already has plenty experience with thoriated tungsten filaments from the 211 and 845s.

Initially it seemed impossible to do that and keep the spec for filament voltage and current. So first experiments were started using oxide coated filaments which I helped to get from one of the large tube manufacturers. But Dr. Schaffernicht wouldn't let go of the initial idea to use thoriated tungsten. He finally came up with a design which enables the use of the bright filaments as can be seen on the photo above.

Here another photo of the tube operating in an amplifier:




Filament voltage and current are exactly to spec. The filaments draw 1.2A at 5V which is the same as the Western Electric 300B consumes.

So how does it sound? The famous question every audiophile wants to get answered. This puts me in a conundrum for several reasons. First I am distributing the Elrog tubes. So I have a commercial interest involved. Please take this into account when reading my findings. Second I never was a big promoter of the 300B. Always seeking different tubes which are less hyped by the mainstream. Like 45 or 801A. Instead of the 300B I often suggested a triode connected 6CB5A as cheap and good sounding alternative. See also my post about that here.

The Elrog ER-300B changes the picture for me. This is the best sounding output tube I ever listened too!

Many might think now of course he is saying that, he wants to sell the tubes. That's why I am very open about this and ask you to take it with a grain of salt. Especially since I have a preference for thoriated tungsten. Also the findings so far have only been done in a single amp. The one I showed in the previous post.

What does 'the best tube I ever heard' mean? After I plugged the tubes in, I was confronted with an almost shocking realism. Gone was the slight softness in the bass which I heard with other 300Bs. The resolution is increased considerably. The beauty of the voices and tone colours of the WE 300B are fully retained.




Since one can easily get carried away in the first moments of enthusiasm, I waited with positing my findings and see if the impression stays after listening for some days. And it did!

One could argue, that it is not really a 300B anymore and I agree. You could call it a transmitting style 300B. The only 'real' 300B is the Western Electric in my opinion. There is also another aspect: The use of the thoriated tungsten demands a compromise. Amplification factor and plate resistance needed to be slightly altered. Amplification factor is a bit lower and the plate resistance a bit higher which results in lower transconductance. Yet the tube will work in any 300B amp. The maximum available output power will be slightly reduced. But that is well worth it, because it makes it a better tube in my opinion and in my ears.

The sound of the tubes sparked several ideas for new stuff. A variety of 300B amps, both SE and PP, and maybe even a 300B line stage.

I am in the process of characterising the tubes to create a data sheet which will reflect this. It is important for Elrog and for me to be very open about this. Detailed updates and figures will be published in future posts after I had a chance to run measurements on more tubes.




The tubes I have in the moment are pre production samples. Elrog is working hard to finalise series production which will take a bit more time than expected. I hope to be able to deliver the first tubes to customers before end of November. The first batch of tubes is already sold out through pre orders. Place your pre order now to get tubes from the second batch which should be delivered in December.

UPDATE : I am not taking pre orders any more at this time since demand is higher than the expected production capacity. I will notify when I can accept pre orders again.


Stay tuned for further impressions and updates

Best regards

Thomas



Monday, October 13, 2014

Making of a 300B Amplifier, Part 3 : Completed Amps

Hi!

I know that many of you are waiting for my report about the Elrog 300B. Please be a bit more patient. I don't want to write out of the first moment of excitement. I rather live with the tubes for some time and give them a thorough listen. What I can say already: This is going to be very interesting!

End of last year I already built a set of single ended 300B mono amplifiers which was meant to be for testing the Erog tubes. So far I only showed the assembly of power supply and amplifiers. But the final part which shows the completed set of mono blocks is still missing. So here is my statement in 300B amplification:





A four chassis affair, monos with separate power supplies for each channel. The photo above only shows one mono block. The 300B is driven by a 10Y through an interstage transformer. Interstage and output transformers are made in Japan by Tango. In this case the transformers are from old production when Tango was still part of Hirata Electric. The interstage transformer is the fabulous NC20 and the output transformer is a permalloy core NY15-3.5S. The latter has not been made any more after Tango split from Hirata and continued under the ISO Tango name. These are very rare and unique transformers. With their 3.5k load they are ideal for the 300B.




Both the driver tube and the 300B are heated with DC for zero hum and to avoid any kind of modulation of the signal by the mains frequency. Due to the extensive use of chokes in both B+ and filament supplies each unit is still quite heavy, although the amp is split into 4 chassis.




Above one channel is equipped with Elrog and there other with Western Electric. The driver configuration brings out the best of the 300B in my opinion and is at least as important as the output tube.




So this is the ideal test amplifier to assess the sound of the Elrogs.




The signal section with WE 300B:




With Elrog:




After I finished the assessment of the Elrog tubes, these amplifiers will be up for sale. Drop me an email if interested.




So please bear with me for some more time until I post my findings about the Elrog tubes. These will most likely come in several parts as I gain experience with them.




Stay tuned!

Best regards

Thomas