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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Friday, September 22, 2017

300B Mono Amplifiers Landscape Style - Part 1

Hi!

So far all 300B amps I built were mainly in portrait chassis as seen here and here or in tower style. Now I have a set of 300B monos in the work in the classic landscape shape.




Here a few photos which give a preview how they are going to look like. Each mono block has it's separate power supply, so 4 chassis total. This is an amplifier section with all parts mounted on the top plate:




Tribute finemet core output transformer on the left behind the 300B output tube. The 10Y driver tube sits at the back for a short signal path from the input jack. It drives a Tribute finemet core interstage transformer which is placed at the front to the right. In between the oil capacitors painted in metallic blue.




The power supply chassis houses a big B+ transformer on the left and all the oil caps for high voltage smoothing on the right. A full wave rectifier bridge with 4 6AX4 or similar TV damper tubes at the front.




Next we see the bare metal plates of amp and PSU:




The top plates on the left and each chassis has an internal support plate which carries the chokes and other components which did not find room on the top plate.




Wiring of the amp section. The 10Y is fed through an input transformer which is placed right beside it (lower right). The chokes are on a second level:




Wiring of the PSU:




The two small transformers are the separate filament transformers for DC filament supplies of 300B and 10Y. All other components are mounted on the internal plate:




Stay tuned for more photos when the amps are finished.

Best regards

Thomas

Sunday, September 17, 2017

News from the ELROG Tube Factory 8

Hi!

Deutsche Elektronenröhren Manufaktur GmbH proudly presents the latest addition to the tube portfolio: The ER284.




This tube is a molybdenum plate version of our 845.




We named it after the Western Electric 284 which was a molybdenum plate tube and had characteristics very close the the 845.




Like our ER242 is a molybdenum version of the ER211 with the same characteristics, the ER284 has the same parameters as the ER845.




Both the ER242 and ER284 are made with new bases from now on. The bases are black with teflon bottom. In addition all molybdenum plate tubes are wired with solid core silver wire inside the bases.




Here the ER284 besides an ER845:




As with the ER242 the molybdenum shows off an orange glow in operation:




These photos are a bit under exposed so that some detail is visible. The filament is actually brighter.




Like the ER242 the ER284 is made in limited numbers and to order. Expect some waiting time if you order these.




Please send an email to thomas -at- vinylsavor -dot- de or info -at- elrog -dot- com if you are interested in this or any other ELROG tube.




Since this summer the 211 and 845 are shipping in the new style with 'inverted' internal structures compared to the older version.





This was done to reduce the heat generated around the bases which enables the use of the tube in amplifiers with restricted air flow around the bases or which have the tubes mounted such that the bottom half is inside the chassis. As for example David Berning amplifiers.





Here is a testimonial from one of the first customers of our new version ER845:

The new production Elrog 845 (with the raised plate structure in the middle of the tube) is a transformation in my Berning 845 OTL amplifiers.

The tube is coherent and resolving from top to bottom in ways that my previous reference Psvane WE replica tubes cannot approach. The musical intent, as difficult as it is to define -- is easy to hear and emotionally 'feel". Delicate bass harmonics, changes of timbre, and subtle pressure changes on strung instruments combine to communicate a greater musical truth.

Bass is much more transparent, articulate and authoritative on my Tidal Akira loudspeakers. Imaging is palpable with increased dimensionality and air. The boundary sounds of the physical recorded venue are better outlined and apparent. You can more clearly tell what kind of space the music was recorded in. 

The noise floor of the tube is discernibly lower. I clearly hear what previously was unintelligible. Transparency to the source is a revelation as is the top end extension and air. The single most important strength of these 'uber' tubes is the focus they are capable of. The analogy is a range finder camera. When you experience music thru these tubes, what you had been listening to seems slightly out of focus.

Congratulations Thomas, you have succeeded in building what I now consider the best sounding 845 ever produced. They are my new pack-in tube reference for the Berning 845 OTL amplifier.

Rick Brown
Hi Fi One
Carlsbad, California
USA





Thanks Ricky, for this feedback!

Stay tuned for more news from the tube factory.

Best regards

Thomas


Thursday, September 14, 2017

The Ultimate Phono Stage - Part 5

Hi!

Another project is finished, the second build of the ultimate version of my phono stage line up.




Fully differential circuit wth Telefunken EC8020 triodes and all signal transformers and chokes in silver.




The total count of silver parts is 20 pieces which splits into 8 signal transformers, 8 plate chokes and 4 LCR RIAA coils.




In addition there are another 8 chokes in the signal chassis. These are secondary to the signal path and are copper wound. These are 4 grid chokes and 4 cathode chokes. This brings the total count of transformers and chokes in the signal chassis to 28! 12 of those are housed under the transformer covers on the top. 3 under each cover. The rest is mounted inside.




The separate power supply chassis houses another 2 transformers and 5 chokes. The circuit is the same as used in the first silver unit which I showed in part 4 and demoed at the High End in Munich.




The color combination is the same as used on my first differential EC8020 phono which was a copper version.




Since my supply of EC8020 triodes is limited and I keep spare replacement tubes for each such phono stage sold, this type of phono stage is only available in very limited numbers. After this one only two more such phono stages will be built.



Best regards

Thomas

Thursday, August 24, 2017

Tube of the Month : The 7A4

Hi!

After the presentation of the 7B4 last month, let's continue the Loktal theme with the 7A4.




As mentioned in last months post, being electrically equivalent to the 6SF5, the 7B4 could be used as the first tube in the Octal Phono Preamplifier. The 7A4 is the Loktal equivalent of the 6J5. So with the 7B4 and 7A4 combination a Loktal Phono preamplifier could be built.


The 7A4 shares the same pinout with the 7B4. But that's where the similarity ends. The 7A4 has a much lower mu of 20 combined with a plate resistance around 7kOhm. Like the 6J5 it is basically one system of the 6SN7 or 7N7 which is the 6SN7's Loktal equivalent.  For complete technical details refer to the Tung-Sol data sheet.  With these technical parameters the 7A4 is a quite versatile tube, fitting for many applications. Besides the mentioned phono stage it could be used in line stages and also as driver for output tubes in power amps. Like all other Loktal types, the 7A4 was only made by a few manufacturers and most of them came from Sylvania. While researching information about the 7A4 I came
across an interesting special tube series designed by Philco. The 'XX' series. This series consisted of the XXB, XXD, XXFM and XXL with the latter being a near equivalent of the 7A4. I found a Tung-Sol data sheet of the XXL. Although often listed as technically identical this data sheet shows a slightly higher plate resistance and also a variation of the amplification factor over the operating points. Nevertheless the two types were regarded as close enough electrically so that many 7A4 tubes also carry the XXL designation. I couln't find much information about the Philco XX tubes and the reasoning behind them. Might just have been a marketing stunt. If anybody has some background information about this, please share.

As always, let's start with a look at the plate curves of the tube:




A nicely linear set of curves. Actual curves are just as good:




Now let's look at some 7A4 tubes. Here we have a Sylvania:




Corrosion of the base is quite common with Loktal tubes and probably one of the reasons why they are not really popular.




A Philco.




This one is marked XXL on the top.




Another 7A4:




This time with dual marking 7A4 and XXL:




This marking was not consistent. Sometimes the box would be marked 7A4 while the tube inside only had the XXL marking.




A National Union 7A4 in beautiful, pristine box.







The base which also omits two of the unused pins as the 7B4:




Sylvania 7A4 tubes:





JAN (Joint Army Navy) tube:





Another military 7A4:





Interesting note on the boy: 50 Hr. Life guaranteed? I can't imagine the 7A4 had such a short lifespan. Maybe this was for some particular critical application? Again if anybody has some more information about this, please share.

Here we have a General Electric tube:




This was of later manufacture and does not have the characteristic large getter area as most other Loktal tubes.

Here an older GE:






The two different GE 7A4 side by side:




Tung-Sol:





Some Philco 7A4s:





Here we have a case of 7A4 marking on the box but XXL on the tube:





Another style box:




And lastly more from Sylvania:






Like the 7B4, the 7A4 does not give much of a light show when turned on:




Let's examine the internals of this one:




Glass removed:




The plate is quite thin in diameter:






The triode system detached from the base:




The heater:





The plate removed, unlike the 7B4 it has an oval shape.




Grid and cathode:






The cathode by itself:




In the close up it can be seen how coarse the cathode coating is:




The grid:





I hope you enjoyed this presentation of the 7A4 and maybe some tube amp builders will get inspired to use it instead of the 6J5 to give this almost forgotten tube some use.

Best regards

Thomas