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, December 9, 2016

SE 211 Amplifier Production

Hi!

A quick glimpse into my workshop showing the current work in progress.




3 Pairs of 211 drive 211 single ended amps are being built. Similar to the 211/211 amps shown last year.




The photo above shows the pre assembled sub modules which go inside the wooden chassis. The top plates for one set of amps are already done. Since each mono block has its separate chassis a total of 12 chassis to be assembled and tested.




The large stack in the back are the modules for high voltage smoothing. 3 chokes and plenty of oil caps:




The shorter stack in front are the modules with the final filter chokes which will reside in the amp chassis. On the right two stacks of modules with the large vacuum varnished B+ transformer and the separate DC filament supplies for driver and output tubes.





The modules with the Tribute output and interstage transformers:




NOS paper in oil caps for the critical sections.






The amp chassis will of course be equipped with Elrog ER211 tubes:




Alternatively these amps can also use the new ER242C.

While one set of the amps will get a similar hybrid rectifier as the amps from last year, the two others will use a bridge with 4 6AU4 TV dampers for rectification:




This is a similar arrangement as in the recently finished differential 300B amps.

The first set of these amps is due to be finished this month and the others will be done in January.

Best regards

Thomas




Thursday, December 1, 2016

ELROG ER242C - 211 With Molybdenum Plate

Update: We received pre orders for the entire first lot which is planned. So we cannot accept any more pre orders for the ER242C at this time. Another lot will probably be started around October 2017.


Hi!

Since I wrote about the future of the Elrog tubes, I am often asked if there will be new developments. I am very happy to announce a new Elrog tube type, the ER242C, a replica of the Western Electric 242C.




The 242 was first introduced by Western Electric as 242A with metal plate. It was later replaced by the 242B which had a graphite plate. In it's final release as 242C the plate was metal again using molybdenum and with a maximum plate dissipation increased to 100W.




It is basically a 211 with metal plate and increased plate dissipation. It can be used in any 211 amplifier without changes.




The photos show prototypes of the ER242C. These are without the characteristic black area and don't have any printing on the glass yet. The final version will get the same blackened area and the printing, similar to the 211:




Here a close up to show the different plates:




Molybdenum is very difficult to work with. After many trials we came up with a 4 piece plate structure which is assembled together with screws.




In normal operation the plates glow orange:




The plates are intended to be operated like that.




Here the tubes are working in my 801A/211 mono blocks.




Some close ups to the beautiful orange glow:





Quite a sight to behold!




We will do a first limited production run of about 20 pairs next year In February / March. If you are interested to get a pair, we are starting to accept pre-orders for the ELROG ER242C. Due to the difficult forming and assembly process of the molybdenum plate structure, these tubes will have a 50% price premium over the standard ER211.




Orders from within the European Union will be handled directly be us. Please contact me by email or phone. Contact information can be found under the Impressum link.

If you are in  the US or Canada you can buy Elrog tubes and pre-order the ER242C through George Lenz of tubesUSA.

I am happy to announce two new distributors for ELROG tubes:

For China, Hong Kong and Taiwan contact Emmanuel Lebreton.

Robert Lai of Live Acoustics represents Elrog in Singapore.

All other regions will be served directly. If you are interested to represent the Elrog brand in your area, please contact me. I hope to announce more distributors soon.







The sound of the molybdenum plate tubes is beautiful. They improve on the qualities of the ER211 with added ambience and resolution. Of course the subjective sound impression of these can vary between different amplifiers and different people might have different perceptions.




I expect the first batch of ER242C tubes to be reserved very quickly. Depending on demand and feedback from the first users we will occasionally make batches of these and might introduce molybdenum plates also as an option for the ER300B




Stay tuned for more news from the tube factory and for new tube type introductions!


Best regards

Thomas



Sunday, November 27, 2016

Tube of the Month : The 417A

Hi!

After the large directly heated tube in last months tube presentation, let's have a look at a tube on the other end of the size spectrum. For this month I selected the Western Electric 417A.




The 417A is a rather modern tube intended for grounded grid operation in broad band amplifiers.

The tube comes in a tiny glass bottle on a 9 pin miniature (Noval) base. The pinout can be seen on the left. The diameter is a bit over 20mm which is typical for most Noval tubes. But it is only about 35mm high. Which gives it a distinctive look similar to the 6AM4. The applications it was intended for required high transconductance tubes and the 417A has plenty of that: 25.000 micromhos or 25mS. This comes with an amplification factor of 43 and a plate resistance of 1700 Ohms. The plate voltage maximum is specified with a rather low 200V which however is quite typical for such tubes. The maximum plate current is 40mA. However these should not be at the limits at the same time. The plate dissipation is 4.5 Watts max. Typical operation as given in the data sheet is 150V and 22.5 mA. Although intended for grounded grid operation, the tube can also be used in other configurations which are more common in audio. It was started to be used among audio amplifier builders in the 1990ies.
A famous example is a phono stage by Arthur Loesch which used the 417A in the first stage. When transformer coupled driver stages in single ended power amps became fashionable the tube often was selected as driver for a 300B. The rather high amplification factor coupled with a low plate resistance seems to make it well usable and enables a two stage power amp. However to my taste the 417A does not provide enough headroom as driver for an output tube. I see it's primary use as a phono stage tube. The high transconductance promises low noise operation. However it also makes the tube difficult to use since it tends to break into self excited oscillations. Careful layout and other measures are required to prevent such oscillations. Quite often these can manifest as audible noise or microphonics although the self oscillations themselves are at very high frequencies far outside the audio band. Probably because of that the tube got a bad reputation for being microphonic and seems to have lost popularity.




Above we see the plate curves as shown in the data sheet. Not as linear as those of directly heated triodes but still quite good for such a high transconductance tube. Here the curves taken with the curve tracer:




It is quite interesting how some tube types go through cycles of being discovered by amplifier builders then overly hyped and finally almost forgotten and rarely seen anymore. Despite the crazy hype around Western Electric and every product baring that name, NOS WE 417A tubes can still be found at tube dealers. Not exactly cheap but given the specs and brand name still reasonable. The 417A was also made by other manufacturers, for example Raytheon and RCA who gave it a standard industrial designation, 5842.




Let's have a look at the original made by Western Electric.




The tube comes in the typical blue and white WE boxes, which changed a bit through the years.





The tube looks great with the manufacturer name and type in the bright yellow lettering.





This tiny tube is a true gem.




Some views from different angles:












As mentioned the tube was also made by RCA:




With double designation 5842 / 417A.




A few close ups of the RCA tube






The RCA and WE in comparison:




Now let's see how the tube looks with the heater lit up.





In the close up we see the finely wound grid:




Some other angles:







It looks nice as the heater lights up the glass up to the tip:








A beautiful tube with interesting specs.




Here a comparison with some other high transconductance tubes:




The tiny WE417A in the middle. A EC8010 to the right next to a D3a. Then the bigger sister, the 437A on the left besides the undisputed high transconductance drama queen, the EC8020.




The last time I used the 417A is probably almost 20 years ago in some experimental phono stage.




In which I remember it performing very well.




Best regards

Thomas