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.

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Thursday, December 18, 2014

6GE5 Mono Amps, Part 2 : Assembly

Hi!

Part 1 about the 6GE5 Monos showed the circuit. In this post I am presenting the assembly steps of the amplifiers.





So far the amps which received the most positive feedback for the design are my 211/6HS5 mono blocks.  So I reused some of the design aspects of those 211 amps for the layout of the 6GE5 Monos:




All the capacitors in the circuit are place in a single row on the left side. The 6GE5 output tube at the front in the middle and the 6AG9 driver beside it. Two separate power transformers are hidden under the black covers. Since the heater windings of the power transformer used does not supply enough current for all the tubes, I used a separate heater transformer for the signal tubes. The 6BE3 rectifiers are placed at the back side.

This is the top mounting plate with just the 12-Pin tube sockets installed:




Most of the resistors in the design are directly mounted to the bottom side of the plate:




All remaining resistors are soldered to the terminal strip.




Mounting of the power transformers:





Most of the wiring done:




Adding the capacitors:





The chokes, output and interstage transformers go inside the chassis:






The finished amp:




The two monos side by side:




Top view:




I have been using these amps for some time and am very happy with the result. Power output is about 4W. Solid frequency response. As mentioned in part 1, I am making a parts kits available for these.

Iron set (power transformers, chokes, output and interstage transformers):

Mono block       EUR 740,- (EU incl. VAT) / EUR 622,- (outside EU)
Stereo version    EUR 1120,- (EU incl. VAT) / EUR 941,- (outside EU)

Iron Set plus oil caps:

Mono block       EUR 860,- (EU incl. VAT) / EUR 722,- (outside EU)
Stereo version    EUR 1360,- (EU incl. VAT) / EUR 1142,- (outside EU)

Full parts kit (excluding chassis and wire):

Mono block       EUR 975,- (EU incl. VAT) / EUR 819,- (outside EU)
Stereo version    EUR 1525,- (EU incl. VAT) / EUR 1281,- (outside EU)

Too expensive? Stay tuned for the entry level version of this amp with just a single choke and RC coupled driver instead of the interstage transformer.

Best regards

Thomas



Monday, December 15, 2014

Elrog ER300B Update 4

Hi!

Another shipment of ER300Bs came in today. All tubes have been retested for matching plate curves and op points. The tubes will be shipped with a measurement protocol of the plate current at a specific operating point.





Almost all remaining pre orders will be shipped this week. The rest will be shipped before the end of the year from the next batch. Some pairs from the next batch are still available. Place your pre order now to secure your pair. After that batch I will not receive more tubes for at least a month.


In the meantime I am getting feedback from the first users of the tube. One such impression was already posted in the previous update.

Cheah from Malaysia was the very first person who put in an order for the ER300B. He just received his pair and plugged them into an amplifier which was built by himself:




This is his feedback:


The ER300B is truly amazing ! 
Just listen to the first few notes form the ER300b already notice the ER300b is out performing the others 300b I own. 
With ER300b music fill with energy and impact. It's portray a rock solid staging and  3d imaging. Tonality is very natural, as good as 45 but with more energy and the ER300b have a deeper sound in every instruments. This tubes are very balance from highs to lows. It's give the right amount of well define bass. 
With ER300b, my amp like double its power. Even with complex music, this tube can handle well, will not out of power.
It's hard to describe the ER300b sound with words until you listen to one. If you are saying ER300b is the best sounding tube you ever listen to, I'm 100% agree with you.


Thanks a lot to Cheah for his feedback and for the photos of his beautiful mono blocks!






Next I have some comments from Michael from Germany who uses 2 pairs ER300B in his Nagra 300p amplifier. I translated them to english:

In the meantime I listened to the Elrogs closely. The waiting was well worth it. During the 40 years of my HiFi hobby I did a lot of 'investments'... the Elrogs are clearly among the lucky ones.

My little Nagra 300p power amplifier improved in pretty much every aspect. Apparent is especially the increased transparency without any harshness or embellishment. Also a nicely balanced sound stage. The tubes which came with the amplifier cannot reach the dynamics and the sovereignty in the bass. I never would have expected such a strong and at the same time refined bass from my amp or any other 300B. All in all it sounds effortless and well-balanced and as such is more music and less machine. Many thanks for this!





Many thanks also to Michael for sharing his experience with the Elrog tubes. Here is the original german Text:


Inzwischen habe ich die Elrog's eingehend gehört. Das Warten hat sich allemal gelohnt. Im Laufe meines bald 40 jährigen HiFi-Hobbys habe ich sicher viel Le(e)hr-
geld bezahlt....die Elrog's gehören eindeutig zu den glücklichen Investitionen!

Meine kleine NAGRA 300p Endstufe hat in nahezu allen Belangen zugelegt.
Auffällig sind insbesondere die gesteigerte Durchsichtigkeit ohne Schärfe oder 
Schönfärberei und der sehr schön ausbalancierte Raum. An die Dynamik und
die souveräne Gelassenheit in den tiefen Lagen kommen die serienmäßigen
JJ's bei weitem nicht 'ran. Einen derartig kräftigen und zugleich feinen Bass
hätte ich meinem Verstärker und auch irgendeiner 300b nicht zugetraut.
Insgesamt klingt das sehr mühelos und ausgewogen und ist damit ein
Stück mehr Musik und weniger Maschine; vielen Dank dafür!


It is great to have feedback about the tubes in such very different amplifiers. I will post more feedback as it comes in. Stay tuned!

Best regards

Thomas

Friday, December 12, 2014

Tube of the Month : The 6BE3

Hi!

This post concludes the trilogy about the tubes used in the recently shown 6GE5 amplifier. Since the signal tubes both are 12-Pin compactron types it was only natural to select the rectifier from that series as well. And the chosen tube was the 6BE3.





Why another TV damper? Besides the various Octal types and the Novar 6CJ3, I already covered a 12-Pin compactron damper in the tube of the month series, the 6CG3.

The 6CG3 would actually be a bit overpowered for this amp. The 6GE5 only draws about 50mA. Even for a stereo version and taking additional current for driver and bleeder resistor into account, the 6CG3 would still be oversized. This is not a bad thing but it has the draw back of rather high heater current. The 6BE3 heater only draws 1.2A. The 6BE3 shares the same pinout with the 6CG3 which is shown on the left. It has a DC current capability of 200mA. This doubles when two of them are used in a full wave configuration. This is plenty even if some derating is taken into account since the 6BE3, as most TV dampers, was never specified for mains rectifier service.
Like all TV dampers, the 6BE3 was designed for extremely high peak inverse voltage. 5kV in this case. Again this needs to be derated for mains rectification. A derating to 50% still leaves a higher peak inverse voltage rating than most classic rectifiers. The 6BE3 is quite similar in it's characteristics to the 6AX4, the TV damper which I mostly use in power supplies. For the complete set of electrical parameters, please see the General Electric data sheet. While I have seen some 12-Pin compactors used in audio amplifiers, I never heard of anybody using a 6BE3 in the power supply. That's why they are sitting in the warehouses of tube dealers and collect dust. They can be bought for next to nothing, which makes them the perfect companion for the 6GE5 and 6AG9 in an amplifier. Here a photo of two 6BE3 in operation:




The 6BE3 was made by all the major manufacturers.

RCA:





Sylvania:






Sylvania / PhilipsECG:




Zenith branded (made by Sylvania):




General Electric:




DuMont:




Tung-Sol:




The characteristics of the 6BE3 are very close to the 6BZ3. In such cases it was a common practice to  combine the types and label tubes with both designations:




6BE3/6BZ3 made in Japan:





These came in a bulk pack of 50 pieces:




Now let's take this one apart to see how it is constructed inside:





Removing the glass reveals a better view of the plate structure:




The top side:




The white spiral provides isolation between the heater wire and the cathode.




Removing the heater with it's isolation spiral:




Close up:




The cathode:




The plate:






A 6BE3 in operation:




A close up to the heater :




I hope you enjoyed the last Tube of the Month post of 2014. Stay tuned for many more tubes to be covered in this series in the next year!

Best regards

Thomas

Wednesday, December 10, 2014

300B drives 300B, Part 1

Hi!

While work on some entry level amplifier designs based on the recently presented 6GE5 tube has progressed (more about that soon) there is also a new 300B amplifier. This time with a second 300B as driver tube to get the full blast of the Elrog thoriated tungsten sound.





One mono block is finished and tested. Shown above. The output transformer is a Tango XE20S. Interstage transformer is the new Lundahl LL2753. With the air gap set for the appropriate DC current it works great with the 300B.


The power supply is external as usual for my designs of this level. Here the amp with it's PSU:





Measurements and adjustments of op points are finished. The measured performance is very promising. The second mono block is almost finished an then the first listening test can begin.




Another version of this amp is planned with Tamura output transformers. Stay tuned for updates!


Best regards

Thomas

Saturday, December 6, 2014

6GE5 Mono Amps, Part 1 : Circuit

Hi!

I often hear people complaining about tube prices and how much better it has been in the old days when prices had been more affordable. I wholeheartedly disagree with this point of view. In fact I think we are in the best possible times when it comes to tube audio. While it is true that the prices of some overly hyped tube types skyrocketed, there are still a lot of dirt cheap tubes which are available in abundance as NOS. Thanks to the internet it is easy to find suppliers for such tubes and data sheets of even the most obscure types are just a few clicks away. I remember when I started to get into tube audio that it took me almost a year just to get the most essential tube data books.

Also the availability of other parts is gerat nowadays. Audio transformers are available in a larger variety than ever.  And there are new tubes still being made with the Elrog 300B being the latest introduction.




If you think some tube types are expensive, compare the prices of them from 40, 50 or even more years ago with inflation in mind. Suddenly even many of the highly sought after tubes appear not that expensive compared to the old days. But as mentioned above, no need to hunt for those mainstream tubes if you are on a budget. I already introduced the 6CB5A as a cheap alternative to the 300B and many amplifiers have been build with this tube. In the Tube of the month post about the 6GE5 I suggested that it could be used triode connected in 2A3 designs.

In the November Tube of the Month post I presented the triode section of the 6AG9 as a possible driver for a triode strapped 6GE5 in single ended mode. All that was missing is a suitable circuit. In order to evaluate the sound potential of these tubes I decided to not use the cheapest possible design but something a bit more advanced, with oil caps and interstage transformer coupling. Once the tubes have been proven to work as expected, simpler circuits can be explored as well as more elaborate ones.

In order to minimize variables, I decided to adapt a proven circuit which is known to sound good. So it will be just the tubes which changed. The circuit which I usually use with the 6CB5A could be adapted with minor changes.




The same circuit description as in the article about the single ended amplifier concept applies, so I am not going to repeat it. The voltages are adapted to the 6GE5 and 6AG9. The output tube runs at about 50-55mA with 300V from plate to cathode, so about 15W plate dissipation. The driver operates at about 200V and 6mA. The power supply is basically the same as described in an earlier Making of a 6CB5A amp post. Read it for a description of the supply.

Just for the fun of it I decided to build two cute little mono blocks. So currents, choke and transformer ratings have been adapted accordingly. To stay consistent with the 12-pin compactron theme 6BE3 TV dampers are used as rectifiers.

The construction of the amps will be shown in the next part. Stay tuned!

I am making parts kits available for this design, both for mono and stereo versions.

Best regards

Thomas