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Monday, May 29, 2023

Tube of the Month : The EL3N


This months tube is an old European output pentode. Meet the EL3N.


This tube was introduced by Philips in 1938 and meant to be used as Class A or Class AB output tube.

The EL3N is indirectly heated and has a side contact base with 8 contacts of which 2 remain unused. The pinout is shown on the left. The heater operates at 6.3V and needs 0.9A of current. A tube which is rarely seen in use nowadays. The Philips data sheet does not give a lot of information besides Class A and Class AB operating characteristics with a measly 8W stated as output power from the latter. I never used this tube myself and the few samples I can show were leant to me. Since the data sheet does not give any plate curves, I took the triode curves with a tracer:

Here are two samples from Philips, branded 'Miniwatt':

The EL3N had the characteristic red band above the base and smoked glass from the 'red series'.

The side contact base:

The only other sample I can show was made by Tungsram:

The box:

A few close up shots:

Since there is no getter applied at the top dome this tube gives a better view to the internals and the grids are nicely visible:

Not too much glow visible from the heater:

That's all for the EL3N. Stay tuned for more tube presentations in upcoming posts.

Best regards


Wednesday, May 17, 2023

The integratred 300B Amplifier


The new integrated 300B amplifier for speakers and headphones is finished and passed all tests.

The amplifier uses a pair of 300B directly heated triodes as output tubes and a 6DN7 per channel for the input and driver section. The latter fits this application well and does a much better job than the ubiquitous 6SN7 which seems to be used in 90% of 300B amps. 

One half of a 6SN7 has a too high plate impedance to properly drive a 300B. Using both halves in parallel works well but will then require another tube to get sufficient gain for an integrated amp. Hence my choice of 6DN7 which has a strong system with low plate resistance which is used as driver and the other medium mu section as gain stage.

This build got three inputs but it can be equipped with any number of inputs. Volume control is a stepped attenuator with discrete resistors. The output can be switched between the speaker connectors on the back and the headphone jacks at the front. The speakers can stay connected when using headphones and are muted in that case. Any impedance headphone can be driven. There is an attenuator switch which lowers the output by about 18dB in case of very sensitive headphones. This way a good volume control range is always given.

Power output is about 6-7 W per channel on 8 Ohm speakers. The output impedance is rather low for a SE amp so that a 6 Ohm speaker could still be used.

The high voltage is tube rectified using a pair of 6AX4 TV Dampers or equivalent. These work into a choke input filter (LC) which is followed by separate LC sections per channel (3 chokes total) for decoupling and absolutely hum free operation. The latter also ensured by clean DC filament supplies. 

The dimensions are :
27cm wide, 40cm deep (plus knobs at the front), 30cm high (to the tip of the tubes)
Weight is 24kg.

The unit does not use any PCBs and is completely hand wired point to point.

Here a few photos from the assembly process. The parts are arranged in several layers in a 3D fashion to achieve the compactness.

Only top quality film caps are used in the high voltage supply. 

The amp is designed to work with any 300B compatible tube (No XLS types with increased filament current).

The standard option is with ELROG ER300B output tubes, two pairs NOS rectifiers and two pairs NOS 6DN7 driver tubes. This package comes at 7150,- Euros export price or 8500,- including VAT within the EU. Plus shipping. The amp can also be ordered without output tubes. In that case the price is 5900,- / 7000,-

Of course the amp can also be ordered with ELROG ER300B-Mo: 7900,- Euros export, 9400,- incl VAT.

Or go for the TM300B as output tube for 9000,- / 10700,-

These prices are valid in the introductory phase and will have to be raised by about 500,- due to the materials cost and labour which this amp requires. Also the free spare pairs rectifier and driver tubes are only included in the introductory phase. 

Since each unit is built to order many customisations are possible. For example no headphone outputs or headphone outputs only with selectable impedance. This concept can also be customised to use other tubes like 45, 46, 2A3, 71A.

Best regards


Friday, May 12, 2023



So far the TM300B tubes were only available to users of amplifier built by me. Since I keep getting requests for these tubes also to be used in other amps, Deutsche Elektronenröhren Manufaktur GmbH made them available for general sale. However in very limited quantities only.

The TM300b was initially introduced in 2020. More sound impressions can be found here and here.

The first batch of TM300B tubes is now being shipped to users of different amplifiers.

If you are interested in a pair of these drop me an email. Please state the amplifier you plan to use them in.

The ELROG website is updated with specs and pricing of the TM300B.

Only one more batch of TM300B will be produced this year.

Best regards


Monday, May 1, 2023

Preview of the Integrated 300B Amplifier


The chassis material for the integrated 300B amp arrived. Here a quick preview of how it will look like:

In March I showed the test build which was used to evaluate the concept. Now a version in the final chassis is being built.

The 6DN7 driver tubes in front of the 300Bs. Two power transformers and a choke are hidden under transformer covers.

At the left corner in the back two rectifiers tubes. 6AX4 or equivalent tubes like 6DA4 and 6DQ4 can be used.

Two more chokes and the output transformers will be mounted  under the top plate.

The first version will also get headphone outputs at the front. Any impedance headphone can be used.

Initial pricing will be 8500 Euros (within EU including VAT) / 7150 Euros (export). Price will be raised by 500 Euros later on. The price includes Elrog ER300B and NOS 6DN7 and rectifiers. Any 300b can be used. The unit can also be ordered without output tubes. Stay tuned for photos of the final build when assembly is finished.

Best regards