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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Saturday, December 31, 2011

Happy New Year!


The year comes to it's end. With it the first year of the VinylSavor blog. I'd like to thank all my readers and especially those who gave comments and valuable feedback.

What is planned for 2012? I will continue the tube of the month series which seems quite popular. There are many interesting tubes outside of the mainstream which are worthwhile to write about and still lots more which are yet to be discovered for audio use. The single ended amplifier concept series was dormant for a while. I plan some further articles  about DC filament output tubes and all DHT amplifiers. There are also some ideas about RIAA concepts which are waiting to be tried. I will write about them if the experiements turn out to be promising. I will report about the progress with my field coil loudspeakers. My all DHT phono preamplifier concept is also waiting to be rebuilt in some nice chassis. I will post picturees of new gear which I build in the making of series. And last but not least my 150W single ended amplifier with the 851 tube is also waiting to be worked on.

If you have some comments about topics which I should cover, please let me know. I'd also like to repeat my invitation for guest articles. There was only one guest article during last year. Hopefully there will be some more in the next year.

No photos of tubes or gear today, just a few impressions from Lindau, where I live. Lindau is situated at lake constance (Bodensee). The old part of the city is actually on an island in the lake and has a beautiful small harbour. You might have noticed the small island with the tree in the background of some of my photos and which is pictured in the first photo in this post. It is a small artificial island called 'Hoy'.

Lake constance is the largest lake in Germany. It lies between three countries: Germany, Austria and Switzerland. At night the lights of the city of  Bregenz are shining from Austria across the lake.

All the best for the year 2012 to you and your families!


Thursday, December 29, 2011

New plate chokes from Lundahl


Lundahl came out with a new plate choke, the LL2743. It is wound on a larger core size as the existing range of LL1667 and LL1668 plate chokes. They come on the same core as the LL1673. This allows higher current chokes for use in the output stages of parafeed amps.

The choke can be ordered with different air gaps for various DC currents. The photo above shows three versions: 50Hy/90mA, 65Hy/70mA and 90Hy/50mA. Like all Lundahl chokes they are wound with two separate coils which can be connected in series or in parallel. The inductance and current values are given for the series connection. Parallel connection will result in one quarter of the inductance at twice the current. This is because inductance has a square relationship to the number of windings. Doubling the windings results in 4 times the inductance. The DC resistance of the choke is 200 Ohm per coil.

The next photo shows the LL2743 in comparison to a LL1668:

The LL2743 complements the LL1667/8 very well, extending the current range of the plate chokes up to 100ma. Of course these chokes can also be used for B+ smoothing if you don't mind the higher DC resistance.

Best regards


Monday, December 26, 2011

Tube Box Art, Part 2: National Union


In this second installment of the Tube Box Art series, I will show how the packaging art work of the vacuum tube manufacturer National Union changed over the years.

Like almost all tube manufacturers, they started with very colorful and beautiful tube boxes which changed to simpler designs over the years. The company was founded in 1929 as a merger of 3 radio tube manufacturers. They produced tubes for about 30 years until the company merged with Eureka-Williams.

The photo below shows the packaging of a NX112A tube (equivalent to the type UX112A):

This was a globe tube form the 1920ies or early 1930ies. When the ST style glass came up, NU changed the packaging. Still quite nice, but a bit more technoid. The next photo shows the box of a 6A6 (predecessor of the 6N7):

This package is probably from the mid to late 1930ies. During the 1940ies the box art got further simplified, but they maintained the green colors. Below a box of a 45 tube:

And their last tube box style, here the packaging of a 71A:

Stay tuned for more tube box art posts, covering manufacturers like Sylvania, Arcturus, also some european brands and many others.

Best regards


Thursday, December 22, 2011

Cool Links: www.kilimanjaro-series.com


During the recent years vintage field coil speakers gained an increasing popularity. Those who have heard a good speaker based on field coil drivers know why. This principle is far better sounding than the more common speaker drivers with magnets. More resolution, more sense of beeing there, more tone, more of everything.

If you are interested in field coil speakers, but don't want to hunt those vintage drivers, of which you can never be certain how good they are after decades of use or storage somewhere in a barn, there are few choices of currently manufactured drivers. One of them is the Kilimanjaro Series by Wolf von Langa. I already used a field coil horn driver from Wolf in a speaker installation and it sounded much better than the TAD 4001 it replaced. I also had the chance to briefly test his field coil version of the Altec 515 woofers. I'm currently in the planning stage of a new speaker set up which will use Kilimanjaro drivers. This is the A2000 horn driver for this project:

For the bass and lower mids I will use the A416 and A515. Below two fotos of one of the woofers:

As much as I like vintage tubes, I feel a bit uneasy to spend a lot of cash for 50, 60 years old or even older drivers. How well are the voice coils still aligned? Have they been abused? What is the condition of the membranes? They sure have soaked up humidity over the decades and are far from their original condition.

The Wolf von Langa drivers are all brand new. No need to worry about aging for decades! For a short while I was tempted to go for chinese copies of a famous WE driver. I'm glad that I did not have to settle for copies but rather got some original work. Precision machined and engineered with brain, heart and soul! And the most important of all: With ears! I know Wolf since a few years and am glad that I can say that we became good friends. He has an exquisite taste, not only in sound and music. The photo on the right shows the creator of these drivers. Thanks a lot Wolf, for pushing the envelope in speaker design. Keep up the good work!

Best regards


P.S.: I will write about the progress of my new field coil based speakers in an upcoming series of articles. Stay tuned.

Monday, December 19, 2011

Lundahl Silver MC Transformer Listening Test


I finally had the time to compare the LL1933Ag transformers against the regular LL1933

The comparison was done with my EC8020 LCR phonostage. The result was quite remarkable. There is a very audible difference between the two. The silver transformers sound smoother, yet have a tad more resolution. A very pleasant sound with no hint of coloration or distortion. Very different than the common prejudice of 'silver sound' would suggest.

All the characteristics of records are more pronounced with the silver transformers. Electric guitars have more twang. Hammond organs sound a bit more dirty. The music has more character through these step ups. Or more correctly stated: the character of the record is better preserved.

I was very surprised since I did not expect a big difference. As some of my posts suggest, I'm quite critical about the importance of cable sound. The difference the silver makes in these transformers is an order of an magnitude more audible than the difference between copper and silver wire when used for internal hook up or interconnects.

Where does this leave the copper LL1933s? Should you replace them with the silver version? Of course these don't make the standard LL1933 a bad performer. It is one of the finest MC step ups out there. If you have your dream phonostage already, consider the LL1933Ag for an improvement. If you do not have a maxxed out phonostage yet, there might be other things to improve first before going for silver transformers.

Best regards


Thursday, December 15, 2011

LCR Phonostage With Variable EQ Curves, Part 4: Listening


This is the final article about the variable LCR EQ mono phono preamplifier with photos of the completed preamp and the impressions from the first listening.

The photo above shows the preamp (left) with the external power supply (right). The two knobs are for independent adjustment of turnover and treble roll off:

The first listening test was done with the controls set to RIAA to verify that it has the same sound quality as the stereo LCR RIAA preamp which I presented a while ago. It uses the same circuit and also the EC8020 tubes. The sound in this setting turned out to be even a bit better, most likely due to the use of the better quality nickel coils and paper in oil capacitors.

Besides the EQ network all other parts in the signal section and power supply are the same. Also the mechanical construction is very similar with the same vibration damping mechanism used for the EC8020 triodes. The photo on the left shows a close up of the subassembly which carries the tube socket. With all these details being the same the difference in sound can be attributed to the different parts quality in the EQ network itself. More interesting than the RIAA setting however were the results with discs with different EQ curves. This was quite revealing. Records which sound a bit screechy through RIAA equalisation get very listenable with the correct treble attenuation. Treble attnuation setting is the most obvious. It also brings live into records which sound dull through the wrong EQ. The differences due to turnover setting are much more subtle but also quite audible.
I rediscovered quite a few of the mono records from my collection which are not very listenable with the wrong EQ setting. Unfortuntaley the phonostage had to leave already to it's new home. I will build another one just like this for myself since this is a must for listening to old mono records. Since the number of possible EQ settings is limited if done with LCR networks (unless the phonostage can become much bigger) I'm also thinking about a variable EQ version of the simpler Octal preamplifier with a wider variety of settings.

Best regards


Sunday, December 11, 2011

Tube of the Month: The 6U10


This months tube is a type with compactron base. Again a tube which is widely ignored by audio people and available for very low cost. A true dumpster diver's dream: The 6U10.

I already wrote a bit about the background of the compactron series of tubes in the articles about the 6HS5 and the 6CG3. So I'm not going into more details about this again. You can read some more information about the compactrons in general in these articles.

The 6U10 makes use of the many pins of the compactron base and integrates 3 triodes in one envelope. All cathodes, grids and plates sare brought out to separate pins. All three systems have a common heater. This still leaves one pin unconnected. Two of the triodes, system 1 and system 3 have the same parameters: a medium amplification factor of 17.5 and a plate resistance of 7700 Ohms. System nr. 2 is a high mu triode. It has an amplification factor of 98 and a plate resistance of 61000 Ohms. All details can be found in the datasheet. The two medium mu triodes are comparable to the systems of a 6SN7. The amplification factor is a bit lower and the plate resistance slightly higher. The high mu triode is comparable to half of a 12AX7 (ECC83).

This makes the 6U10 a very interesting tube for audio purposes. The integration of three separate triodes into such a small bottle could enable very compact amps or preamps. The glass envelope is less than 4cm high. Compared to the common Noval based tubes the diameter is relatively big at about 3cm. Most important for the usability in audio are the parameters of course and especially the linearity of the plate curves. While it is not quite as linear as for example the 6SN7 or 12AX7, the plate curves still look quite good, especially if you pick a good operating point and a linear region. The picture below shows the curves of systems 1 and 3 on the left and the high mu system 2 on the right:

These compare very well to actual plate curves taken from a tube with a curve tracer:

This looks pretty good! Also the sample to sample consistency is quite good. The systems 1 and 3 within an envelope also match quite well. The traced curves on the next photo are picked from a random tube. The plate curves of system 1 are drawn with a solid line and system 3 with a dotted line. They match very well.

Now that we have examined the technical qualities of this tube, what could it be used for? How about a preamplifier with phono section with just a single tube per channel? The high mu section could be used for initial amplification of the small signal from the cartridge. Section 1 for the second stage for further amplification and section 3 for the output stage. Here is a schematic of such a preamp:

As drawn it is just a phonostage with enough gain to use it with a MC cartridge without step up transformer. Gain is about 55dB. Don't expect super low noise performance out of this. For lower noise operation use it with a MM or with MC step up transformer. In such an application a volume pot and input selector could be added in front of the third stage and it becomes a full function preamp. Here is a photo of the circuit in an experimental prototype:

It tested quite well, especially when considering the cost of the parts. If you want to build this circuit, please keep in mind that the EQ networks should be checked and trimmed in circuit. Gain can be changed a bit by using cathode bypass caps. I only used one in the last stage to keep output impedance low.

Now some more potos of the tube itself. This is a close up showing the base of the tube:

Here the three systems can be seen:

And finally a series of photos with the tube lit:

I hope you enjoyed this last tube of the month article for this year.

Best regards


Sunday, December 4, 2011

LCR Phonostage With Variable EQ Curves, Part 3: EQ networks


Here is an update on the progress of the mono phonostage with variable EQ. This is a photo of the inside of the finished preamp:

The inside is quite packed and it was a bit tricky to fit everything into the given space. Especially the usage of high quality paper in oil caps made this a challenge.

The photos on the left show the inductances for the EQs. They come with many taps for adjustment of the inductance in small steps. Before mounting, the resistors parallel to the inductance are soldered directly to the coils, between the taps which give the closest inductance to the calculated inductance. The upper photo shows the coils for the low frequency EQs. They get a third resistor soldered to the midpont of the two resistors which are in parallel to the coil. The capacitor to ground is later hooked up to this. The second photo pictures the high frequency coils. Since the high frequency networks only have one time constant, there is no resistor in series to the capacitor to ground. This cap will later be directly connected to the midpoint of the two resistors.

Here is a photo of the phonostage before addition of the EQ networks:

The switches for EQ selection are on the right side. The next photo shows how the coils are mounted above them:

And finally a photo with everything in place and wired up:

Eveything ready for testing and insertion into the wooden enclosure. Stay tuned for part 4 with photos of the completed mono phonostage.

Best regards


Tuesday, November 29, 2011

Tube of the Month: The E55L


This months tube is a wide band output pentode. The industrial tube type 8233 with the european designation E55L.

For LCR phonostages I like to use very high transconductance tubes like the telefunken EC8020 or Western Electric 437. Unfortunately these tubes are very rare and increasingly difficult to find. I'm often asked which alternative tubes could work in my LCR circuits. There is not much else available in terms of 'real' triodes. But there are some pentodes which can be transformed into high transconductance triodes by connecting the screen grid to the plate.

The E55L is one of them. It has been manufactured by such famous companies as Amperex, Mullard, Philips and probably others. The Philips datasheet classifies it as a special quality pentode designed for the use as wide band output tube. It comes with a 9 Pin Magnoval base. Triode connected it has a transconductance of 45 mS (45.000 micromhos) with an amplification factor of 30. This translates to an internal resistance in the region of only 600 Ohms. Perfect to drive a low impedance LCR network with a transformer with a slight step down of maybe 2:1. This means that it will still achieve a good gain in such a set up which is important for the use in a phono preamplifier. Another important aspect for this application is microphony. I have not tried the tube yet so I have no experience how well it is usable in such small signal applications.

Of course it seems also perfect to be used in it's intended application, as output tube. Probably good for a single stage 'spud amp', triode strapped in SE with 2W. The tube is surprisingly compact for a power output tube. About 30mm diameter and just about 60mm high. I'm usually not very fond of high transconductance tubes as drivers for output triodes. Most of them do not offer enough headroom for my taste. I like to have at least 6dB of headroom in the driver. This tube seems feasable as a driver for output triodes. Due to the low plate resistance it would be perfectly ok to use it with a 1:2 step up interstage transformer which would yield the headroom I'm looking for. Of course it could also be considered to be used as a pentode. Many possibilities to use this tube. Many people have objections against the use of a triode strapped pentode. I have no issues with that. What matters to me is how a tube performs, it's linearity and of course the achievable sound quality. The triode connected plate curves which are shown in the datasheet look very promising:

The curves look very linear. But how does it perform in real life? Here a scope screen shot of the plate curves taken from a sample:

Looks very good to me! The first two grid lines are a bit closer to each other which indicates that it is better to stay clear of the 0V grid voltage. I anyways always insist on a large headroom and try to avoid that the grid gets more negative than -1V even when driven at full signal. The grid lines in the screen shot are spaced apart in 1V steps. I also noticed a good sample to sample consistency. It is fairly easy to find closely matching tubes. And this is matching plate curves not just matching at a single operating point.

Let's have a closer look at the construction of the tube:

This photo shows the peculiar shape of the plate. It is narrowed in the center, coming closer to the cathode and grid electrodes. Apparently it is just this part which is responsible for the tube characteristics. The next photo shows another interesting detail. The tube does not have three wire grids, just two. Grid number three really is a beam forming plate:

That is the shiny boxy structure which can be seen through the holes in the plate and which extends beyond the two micas which hold the plate. The next photo shows a close up of the grid structure:

Note the precisly wound grid wires. The more coarsely spaced screen grid wound between the finer control grid and beam plate. In the upper right corner it can be nicely seen that the opening in the beam plate is exactly below the part of the anode which narrows closer to the grid structures.

The photo on the left with a close up of the pins confirms that the grid nr 3 pins are actually connected to this box structure. This photo also shows the Magnoval base which is not to be confused with the very similar Novar base. The Novar based tubes have the exact same pin spacing as Magnoval tubes. Only the pin diameter is different. A Novar tube would fit into a Magnoval socket but have loose contact. Make sure to use the correct socket with this tube. Magnoval sockets are readily available both as old stock as well as current manufacture.

The photo above shows a currently produced socket from China on the left and an old production one on the right.

As mentioned above, this tube was made by various manufacturers. The Philips E55L shown on the right has the exact same internal structure as the Amperex tubes shown above. So they were probably made in the same factory.  This tube prominently displays a SQ logo on the other side which stands for special quality. The datasheet states a life time of 10.000 hrs for these tubes. Definitely a tube just waiting to be used for audio applications. I'm looking forward to give this very special tube a try. Most likely I'll first use it in a LCR phonostage. I will report about this in future posts. Stay tuned!

Best regards