Tube of the Month : The 6AG9

Hi!

Last month I showed the 6GE5 compactron beam pentode and mentioned it's usability as an output tube in a single ended amp. I went through the compactron series tubes to find a suitable driver. And this is what I found: The 6AG9

Since I have a preference for all triode amps, I concentrated on triodes only. There are quite a few of them in the compactron series. Some combined with other triodes, diodes or pentodes in one bottle.

The 6AG9 contains a triode and a pentode. The triode section has an amplification factor of 39 and a plate resistance of 8500 Ohm. Quite similar to the values of the 6N7 which I like to use as driver for small output tubes. This would make it usable in a 2 stage amp with transformer-, LC or RC coupling. The heater current is a bit on the high side for such a triode, but that is because it also needs to supply the heater of the pentode section. A quick glance into the data sheet shows some nice plate curves of the triode section. A check of prices showed a nicely low cost of $3-4 for the tube. It seems to be an ideal companion for the 6GE5! These are the plate curves as shown in the data sheet:

And this is how it looks like in real life:

Quite alright if the region to the left is avoided!

Most 6AG9s in my stock came unmarked in bulk pack like those above.

Here a 6AG9 mage by General Electric:

The 12-Pin base:

Let's have a look how it is constructed inside!

Removing the glass reveals a better view of the details:

The pentode section takes up most of the space inside. The triode section (top) is separated by some space and a screen from the pentode (silver sheet of metal).

A view of the side of the pentode section:

The top:

The heater wire can be nicely seen coming out of the top and connecting across the tube between the sections.

The heater wire removed:

The part with more folds heats the pentode.

The triode section:

The triode electrodes separated:

The grid:

Cathode:

The triode grid is circular shaped:

The shield which separates triode and pentode:

The pentode section, cathode, control grid and screen grid on the left, plate and suppressor grid on the right:

The grids separated from the cathode:

The control grid has an extremely fine pitch between the wires:

A very well made tube, completely overlooked by audio designers!

In the meantime the tube serves as driver in a 6GE5 amp. Stay tuned for a report.


Best regards

Thomas

Elrog ER300B update 2

Hi!

New tubes just arrived.

The issue with the fragile filaments has been addressed. First measurements show perfectly identical plate curves for matched pairs. The first pair is running in my amps and sounds as beautiful as the samples which I tested in October.

The new tubes also have a different base.

I will run extensive tests on each pair over the weekend. If all tests are satisfactory I will start shipping tubes next week. Thanks to everybody who put in a pre order for their patience. I expect to ship all pre orders within the next 3 weeks.

I am now also taking new pre orders.

The price of the tubes is 975,- Euros per pair within the EU (including VAT) or 820,- Euros export price outside the EU.

Best regards

Thomas

Live from Berlin : ETF 2014 - Part 20

Hi!

The Eruopean Triodefestival 2014 is coming to it's end. Systems are dismantled and loaded into cars. This is my last report of the event. As I already announced in a post in October, my friend Frank and myself did a demo of 78 rpm Shellac records.

Frank brought his Thorens turntable, equipped with two arms from Thomas Schick:

One of the arms is equipped with a vintage Ortofon mono cartridge with 65um needle for Shellacs:

This was connected to a variable EQ phono stage which I made. A 6AH4 preamp served as line stage.

Hoger and Oliver set up one of the JBL 4355 with an amp for us to complete the set up:

Frank did the demo with a beautiful selection of Jazz records ranging from as early as 1917 and spanning 30 years to 1947. Here he is seen during an initial test of the set up before the demo started:

Frank shared his amazing knowledge about Jazz and had many interesting stories and facts to tell. And he had lots of fun himself:

A highlight was the Polydor electric gramophone which he brought as well:

A beautifully made piece of furniture. When you open the lid it gets even better:

The tonearm is nick named the bear paw, because of it's shape.

The tonearm is equipped with a steel needle.

The needle lasts exactly for one record. That's why these needles were sold in packs of 100 or even more. The tonearm tracks with about 70grams of force and thus plays virtually without surface noise. It has a high output level and is connected directly to the line stage.

Here another clip:

This was a great festival with a lot of interesting stuff. I think this year there was more diversity in systems, amps, preamps and turntables than ever.

Many thanks to the Berlin team for the organisation of this great event. Next year the ETF will be hosted in Denmark, north of Copenhagen.

Looking forward to ETF 2015!

Best regards

Thomas

Live from Berlin : ETF 2014 - Part 19

Hi!

At every ETF there are plenty EMT turntables

Indestructible classics which play and play and play.

C'est ne pas un Nagra. Le Nagra c'est caca. C'est un Stellavox...

... the response of the proud owner of this beautiful portable reel to reel when I asked him if this is a Nagra.

Best regards

Thomas

Life from Berlin : ETF 2014 - Part 18

Hi!

The Austrian gang started setting up a system yesterday which was up and running today.

A lot of soldering went on until late yesterday evening:

David Haigner brought some speakers which are in prototype status.

The system filled the huge room with great sound.

Best regards

Thomas

Live from Berlin : ETF 2014 - Part 17

Hi!

Here a random photo collection of gear at this years ETF.

Beautiful Siemens amplifier.

Some serious equipment for measurements:

These guys will definitely not run out of DVMs. And of course the classic Weller soldering iron in light blue:

This is a record cleaning machine. I am not joking:

Turntables everywhere:

Check out this tonearm:

Creative way to add some additional weight:

C'est un Nagra. C'est suisse. C'est très, très précis:

Best regards

Thomas