Tube of the Month : The 274

 Hi!

This month is rectifier time. Meet the 274 family of tubes.

The 274 is a classic full wave rectifier tube with two diodes in one bottle sharing the same cathode. It was introduced by Western Electric in the 1930ies.

The 274 comes in two flavours, The 274A and 274B. Both share the same technical specs but have different bases. While the 274A came out with a 4 pin UX4 base, the 274B was later introduced as well with an 8 pin Octal base (of which only 4 pins are used). The respective pinouts can be seen on the left. The 274 is a directly heated rectifier which means the filament serves directly as the cathode. The filament operates at 5V and 2A. The tube was designed for full wave rectification with the plates connected to either end of a high voltage winding of a power transformer with center tap. The output

voltage can be obtained from either end of the filament or from a center tap of the filament winding on the power transformer. The high voltage winding center tap carries the ground. Like all tube rectifiers the 274 is best used working into a choke input filter. It can work also into a capacitor input filter, however the Western Electric data sheet specifies a maximum of 4 uF of load capacitance. While the original WE274A data sheet lists a maximum rectified output current of 140mA, this was later uprated to 225mA when the WE274B was released. In 2017 Deutsche Elektronenröhren Manufaktur GmbH released the ELROG ER274A and ER274B as modern versions which can replace the original tubes. While the Western Electric 274s used oxide coated filaments the ELROG 274s use thoriated tungsten.

Here we see the ELROG ER274A and ER274B

Both versions share the same construction and only differ in the base.

The ELROG rectifiers use a vertical arrangement of the two plates while other manufacturers mount them side by side.

They come in the straight sided glass bulb and construction which is characteristic for ELROG tubes.

Of course a post about the 274 would not be complete without also showing a Western Electric tube.

Here we have a WE274A with engraved base, a very rare item.

Some details of the tube:

Datasheet included in the box:

And now as always some photos with tubes glowing.

The thoriated tungsten filament of the ER274A is clearly visible at daylight.

And more so at night:

I hope you enjoyed this tube of the month post with both vintage and modern versions of the 274 rectifier. You need more output current or want to load the rectifier with more capacitance? Stay tuned for next months tube presentation.

Best regards

Thomas

SE 300B Mono Amplifiers

Hi!

Here another set of amps which will be shown at the Munich High End next week.

These are similar to previously built 300B amps in tower style chassis.

Except two of the TV damper tubes are replaced by an ELROG ER274B.

Top View:

ELROG ER801A driver and ELROG ER300B output tube.

Visit room F231e at the High End to listen to these amps.

Best regards

Thomas

Deutsche Elektronenröhren Manufaktur GmbH Anniversary

Hi!

Exactly one year ago I announced the founding of Deutsche Elektronenröhren Manufaktur GmbH as the new manufacturer of ELROG tubes.

A lot has happened during the first year. Many changes have been implemented in the tubes. Especially the 300B to resolve the reliability issues it had during the time of production under the old Elrog company. I am happy to report that since production is running under the new company we only received one failed tube back from the field, which got replaced on warranty of course.

On the photo above a pair of 300Bs of recent manufacture. The printing on the glass has been updated and now also shows the company name. Otherwise construction remains unchanged.

End of last year we announced the first new tube type, the 242, a molybdenum plate version of the 211. Producing the first batches took longer than we anticipated, but the first pairs have been delivered and everybody who put in a pre order will receive his tubes soon. I'd like to thank everybody who pre ordered this tube for the support and patience. Those who wanted to place a pre order but had been asked to wait: We will first fill all existing orders which will take until September. Then we will accept orders for the 242 again.

I have been asked if we plan to introduce a similar variant of the 845. Yes this is in the planning and we are producing first prototypes. This tube will be named 284. I will announce availability on the blog, which will probably be around October.

During the High End fair in Munich we launched our first rectifier, the ER274B. Since the ER274A is the same tube with UX4 base instead of Octal base, we decided to make that one as well:

Both the ER274A and ER274B are available and  can be ordered.

In the last factory update I announced plans to develop ELROG 801A and 50 and opened a crowd funding campaign for this. Although we did not quite reach the anticipated number of pre orders, we decided to go ahead with the development. Thanks to everybody who supports this development with his pre order. Development of the tubes and making of tooling is starting in September and we expect to ship the tubes by end of this year. here a photo of a prototype of the 50 which was already made by the old Elrog company:

And lastly I'd like to announce that the 211 and 845 are now being made in a new style.

The old style 211 and 845 generated a lot of heat around the base since the electrode system was mounted close to the bottom. There had been good reasons to do that, namely short signal path and rigidity. However some amplifiers have poor ventilation around the bases which could cause heat issues. So we decided to do a redesign and move the internals closer to the top.

This greatly reduces the heat around the base by some 50 degrees Celsius.

Electrically and sonically we could not detect any difference compared to the old tubes.

Now the glow is much better visible from the top, since the getter is fired around the base.

Thanks to all who supported Deutsche Elektronenröhren Manufaktur GmbH. We are looking forward to our second year and the introduction to all the planned new developments.

Best regards

Thomas