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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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Monday, January 28, 2013

Music: Milt Jackson & John Coltrane, Bags & Trane

Hi!

This is another one of my favorite Jazz records. Milt Jackson and John Coltrane on the album Bags & Trane:




A great record with two giants of Jazz. Milt Jackson, a member of the Modern Jazz Quartet, the greatest vibraphone player and John Coltrane a genius on the saxophone. This was the only recording with these two musicians together.

Bags & Trane was released on the Atlantic label in 1961. The title of the album is composed of the nicknames of the two musicians. The first track, which is named like the album, starts rather calmly with a duet of Coltrane and Jackson, complemented by percussion and bass in the background. The opening sounds very much like other Modern Jazz Quartet titles. After about a minute it gets more serious when Coltrane plays solo. He hands over to the piano, which is followed by an amazing bass solo. The bass is played with a bow, rather than picked. This bass solo is full of tone and colour. After the bass solo, Coltrane and Jackson end the title playing in a duet again. I remember playing this piece on the European Triode Festival 2003 in Langenargen through my EC8020 differential phono stage. It received a lot of applause.

Although very different, Coltrane's style blends in nicely to the Modern Jazz Quartet sound. However he tends to dominate whenever the action is handed over to him, especially noticeable during the first title on the second side: Be-Bop. A fast piece in which Coltrane gets carried away and the other musicians have a hard time to keep up.





A great classic Jazz album which should not be missing in your collection, if you are into such kind of music.

Best regards

Thomas

Tuesday, January 22, 2013

Music: Marilyn Monroe / Yves Montand, Let's Make Love

Hi!

Todays record is very different from the recently presented albums. The Soundtrack of a musical comedy film from 1960. Marylin Monroe and Yves Montand in Let's Make Love.




The album contains some famous Monroe hits like the song which is named after the movie: 'Let's make Love', 'My Heart Belongs to Daddy' or 'Incurably Romantic' . These are as you would expect them with Marilyn's sexy and vibrating voice. Very well performed and fun to listen too. But there are also some other much more interesting tracks. My favorite: 'The Strip'. A very interesting instrumental piece woich starts with some very dynamic percussion. Then a groovy piano kicks in which hands over to a bass. The bass drums on this beat are kicking very low. The piano has incredible attack. The bass is recorded with tons of color. Another instrumental track is called 'Latin One'. As the name implies it is a piece with latin style, but merely a hint of it. It has a lot of free jazz elements and could well have been improvised. Very percussion driven complemented by a piano. A title which you would not expect from such an album.

The record was released on the Columbia 'six eyes' label which is known for excellent recording quality. The voices on this album are vibrant and lively with lot's of goose bump potential. My copy is recorded in mono. Not sure if it was ever released in stereo too. Even being mono the album surprises with a lot of depth. Very different from modern audiophile recordings. The treble is a little bit attenuated, but not too much to loose detail. Lows are surprisingly well defined and powerful. Where this album delivers is in terms of atmosphere and timbre.

My copy of this album is quite worn, I got it from a flea market. Still it is fun to listen to. When the music starts it makes you forget about klicks and pops and it just draws you in.





Best regards

Thomas

Saturday, January 19, 2013

Tube Box Art, Part 11: DuMont

Hi!

As far as I'm aware DuMont relabelled tubes from other manufacturers, most probably mainly Sylvania.  Their boxes have a simple yet very interesting and unique style.




I actually only came across two different box styles from DuMont. I believe the one in the next photo is older:


 
 
These boxes contain Octal TV dampe tubes. Other sides of the same boxes:
 



The top flaps showing their contents: 6aX4 and 6AU4 tubes:




The bottom flaps:




More interesting are their later boxes in a gold color:






 
 
These boxes contain an octal and a 9-pin miniature tube.
 



As with mot boxes the tube types are indicated on the top flaps. here we have a 6AX4 and a 6AM4:




I hope you enjoyed the presentation of the DuMont Tube Box Art. Say tuned for more articles about tube box design.




Best regards

Thomas

Saturday, January 12, 2013

Tube of the Month: The 6CB5A (revisited)

Hi!

The 6CB5A was already covered in the very first Tube of the Month post of my blog. It still is my favorite choice of indirectly heated output tubes. I saw some increasing interest in this tube during the recent months and I just finished a new amplifier which uses this tube. So I thought it deserves another covrage as tube of the month.




The technical aspects of the tube have already been covered in the post in 2011, so they won't be repeated here. Instead I'd like to show more photos of various 6CB5A tubes and also it's construction details.

Here a small selection of 6CB5A tube boxes from various brands:




The tube was made in various variations. Even tubes from the same manufacturer can differ in construction. Some have cooling fins for the screen grid, some don't. Some have the getter applied at the top and others somewhere at the side. The plates can have various shapes.

This is the most common version I have seen from RCA:




A quite different one, also from RCA:




While the first one has the getter at the side, the second one has it in the top. But a more significant difference are the cooling fins attached to the support rods of the screen grid in the second tube, while the first one does not have this additional cooling. The plate structures also differ quite significantly.

The 6CB5A is a good example of cross branding. The second RCA from above actually looks remarkably close to a General Electric version:




The internal construction of these tubes is almost identical. Only the size of the cooling fins is a bit different:




Could be they sold tubes to each other or sourced the same parts from a common supplier.

The Tung-Sol on the left in the picture below has the exact same internal construction as the GE:




Only the base of the Tung-Sol is much wider. The next photo shows a Raytheon compared to the same GE:




These two are absolutely identical, also the size and shape of the cooling fins is the same.

The next photo shows a different 6CB5A variant from General Electric next to a Sylvania which looks extremely similar:




These have  a single cooling fin attached to the screen grid support rods:




Yet another variant, Raytheon branded:




This one has the cooling fins in peculiar shapes:




Next a 6CB5A from DuMont:




Although DuMont did not have it's own tube manufacturing but sourced form other companies, I have not seen a 6CB5A from other brands with the same construction as this.

So the 6CB5A is a great example for the cross branding during the tube era. It seems that even the big manufacturers occasionally sold tubes to each other and just slapped their brand names on.

The earlier variant of the tube, the 6CB5 without the A-suffix, was made in a beautiful ST shape:




Besides the different shape it also had a wider base. 6CB5 and 6CB5A are pin compatible, but if the socket is mounted below the chassis, the hole above the socket needs to be much wider for the ST shape. Some of the 6CB5A versions with straight sided glass also have this wider base, like the Tung-Sol shown above. The next photo shows the bases in comparison:




The 6CB5 plate voltage rating is a bit lower. Apparently the 6CB5 was only made over a relatively short time. While the 6CB5A is commonly available, the 6CB5 is quite difficult to find.

Now after we saw different variants of the tube, let's take one apart to check out the internal construction. We will use this RCA tube:





First we remove the top cap (plate connection) :




Then the glass has to come off:




Now we have a better view at the internals. The top end, showing the mica disc which aligns all the electrodes and supports them inside the glass:




A close up showing the heater inside the cathode:




The bottom mica and all the connections between electrodes and base:




A close up from the other side:




Next the top mica gets removed so that the plate can slide off:




Now we see the beam forming plate and the grid around the cathode. But wait a minute, we see one grid only? It is supposed to have two grids between cathode and beam forming plate, the control grid and screen grid. Let's have a closer look:




Now we see both grids. The screen grid wires are wo well aligned to the control grid, that they are difficult to see. The top mica was already removed so the alignment is a bit skewed, because the support at the upper end is gone. That's why both grids become visible in that photo. A close up:




This photo also nicely shows the cathode coating. A quite rough surface!

Let's have a look from the top:




A close up:




The grid wire seems to be gold plated for reduction of grid emission and the screen grid is coated probably for better heat dissipation. Let's pry the beam forming plate away to get a better view:




Zooming in:




Now the spray coating on the screen grid is nicely visible. The alignment of the grids got destroyed by removing the beam forming plate.

Grids and cathode separated:




Another photo of the beautiful control grid:






The control grid with a scale to give an impression of the dimensions:




Since the tube has a low amplification factor, no tiny distances are needed. The grids are a bit less than a millimeter apart. But the precise alignment of the two grids is spectacular.

Let's have a look at the cathode and heater which is now removed from it:




The black stains got onto the cathode when I removed the grids.

A close up of the cathode surface:




And a close up of the heater, which has a rather thick insulation:




As mentioned above, this is still my favorite indirectly heated output tube. Several amps with this tube have already been shown on my blog. The owner of the first 6CB5A amp I built is still happily using it every day. The 6CB5A seems to be very robust as I have not seen any problems with it so far.

I just finished another single ended amp with a triode connected 6CB5A:




This is a quite elaborate implementation of my 6CB5A concept. The driver tube is the 6N7. Interstage transformer is the Tango NC20F, output transformer is Tango FC30-3.5S. The power supply is external in it's own chassis. Here a photo of amp and power supply together:




The amp during construction: Some heater and signal wiring done:




The inside of the finished amp:




And the inside of the power supply:




Another view of the amp:




And finally some shots of a 6CB5A in operation:




The glowing heater from the top:




The bottom side:




I hope you enjoyed this first Tube of the Month article of 2013! Stay tuned for many more posts about interesting vaccum tubes!

Best regards

Thomas