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Wednesday, January 25, 2023

All DHT Amplification


Like many music lovers, I arrived at vacuum tube amplification at some point in my life. From there the next step was to discover the magic of directly heated triodes (DHTs) and among those especially triodes with thoriated tungsten filaments.

Once I settled for DHTs as the output tube of choice, the next logical step was to extend the use of them to the driver position in the power amp and ultimately to the preamp.

That led to the development of my 10Y line stage range which spans all the way back to the late 1990ies when I built the very first prototype. Back then this was solely for my own use and as a hobby.

Now about 25 years later the 10Y preamp is a corner stone of my product offering and together with the 801A drive 300B power amps. My entry level to all DHT amplification from line level to speakers.

Not only is this combo only using directly heated triodes in the 3 amplification stages from line source to speaker. But since the introduction of the ELROG ER300B, purely with thoriated tungsten filaments throughout the signal path.

Furthermore with the use of input, interstage and volume control transformers no coupling capacitors in the signal path and no resistors. For an uninhibited musical flow.

And in this case equipped with TM tubes throughout.

Various options are possible to individualise these units

This preamp has two balanced inputs which are configured for different gains to adapt for different output volume of sources. In addition it has 3 single ended RCA inputs. Both XLR and RCA outputs are standard on each 10Y preamp.

If you are interested to experience the All DHT magic yourself, drop me an email to discuss your very own set up.

Best regards


Monday, January 16, 2023

Tube of the Month : The EF6


Last Month we had a European triode. This month we stay in Europe with the presentation of a pentode. Meet the EF6.

Niclas of Sweden contacted me after my appeal to help keeping the tube of the month series alive. He sent several different interesting types which I do not have. Hopefully others will follow as well and lend me some tubes to take photos.

I am starting with an indirectly heated pentode form Niclas' care package. The EF6 which was developed for use as audio amplifier or grid detector. It has a P-Type side contact base and a top cap which is connected to the control grid (g1). The pinout is shown on the left. The EF6 has a rather unusual appearance due to its bright red coating. Underneath the red coating there is a metallisation for screening the tube. The tube has a 6.3V heater which only consumes 200mA of current. You may refer to the Philips data sheet for a full set of technical specifications. In the data sheet the low distortion of the tube is mentioned and capability to deliver large voltage swings suitable to drive output tubes. The data sheet shows a set of plate curves in triode mode which indeed looks impressive:

Taking the curves from an actual sample required hooking up the tube with clip leads due to lack of a suitable socket.

Definitely an interesting tube. Especially if you are keen on using less common types in your projects. I will return the tubes which were lent to me so no project from me in sight using the EF6.

Here we have a EF6 made by Valvo.

The base:

A small area around the grid top cap remains uncoated in order not to short out the signal.

Some details of the box:

Next we have a Philips EF6:

And lastly a EF6 made by Tungsram:

Due to the coating no glow is visible when the tube is in operation. Also no dissection of a tube since they do not belong to me and it would be a shame to sacrifice any of these beauties.

Hope you enjoyed this first tube presentation of 2023. many thanks to Niclas for lending me these tubes. I hope more people will follow his example. Rest assured all tubes will be returned promptly after taking the photos.

Best regards


Saturday, December 31, 2022

Happy New Year!


Another year comes to it's end.

It is time to say goodbye to 2022 and hello to 2023.

In terms of amplifiers built, this was the year of the 300B since most amps used it as output tube.

And Deutsche Elektronenröhren Manufaktur GmbH introduced the 4th ELROG 300B variant.

And two new versions of ELROG 801A which are used as driver in all those 300B amps.

Maybe it is time that the 300B finally get's it's spot in the Tube of the Month series.

Speaking of the Tube of the Month series, this months post was number 144. I am about to run out of tubes which I can present.

So here is a shout out to all who like to see more tubes shown in detail: If you have any interesting tubes which would be worthwhile to show as tube of the month, please drop me an email. I am looking for people who can lend me tubes for taking fotos. The tubes will of course be returned promptly and unharmed. I am especially looking for some European types. For example ECC81/82/83/85, EL34, PX4, PX25, C3g, etc.

The soldering iron will not see much rest in 2023 since new projects are already in progress.

Like this 10Y line stage which is almost complete and needs to undergo testing before being shipped.

It will be equipped with TM801A tubes and of course will be used to drive a set of 300B monos.

Which are going through final assembly in January.

But other tubes will also be used and there is a new project in the pipe with two 6CB5A triode wired in parallel single ended configuration.

This will be a new development offering more than 10W per channel without using transmitting tubes like 211 or 845.

I am planning to start a few more new developments with less common tubes.

Also expect some exciting new ELROG tube types to be released.

Many thanks to all of you for a great year 2022.

I wish your families and yourselves

Frohes neues Jahr
Happy New Year
Bonne Année
Feliz año nuevo


Sunday, December 25, 2022

Tube of the Month : The RE084


This months tube is a rather ancient triode, the RE084.

The RE084 is a direct heated triode with a very low power filament. Presumably intended for use in battery powered equipment. It was introduced by Telefunken in 1927.

The RE084 had the Europa 4 Pin base, a base used by european manufacturers for directly heated triodes. The pinout is shown on the left. As mentioned above it has a very low power filament which only needs 80mA current at 4V. The intended use was as small signal audio amplifier tube in radio receivers according to the data sheet. It has an amplification factor of 15 and a plate resistance of 10kOhm. Philips made a similar tube which they named A415 and Valvo called theirs A408. I do not have any of these tubes myself, but thanks to my friend Josef from Vienna who lent me some samples of his collection of exotic tubes, I can present this tube to you today. None of the data sheets which I found showed plate curves. So I took them myself with a curve tracer. The settings are: Plate voltage: 50V / step horizontal, plate current: 5mA / step vertical, grid step 2V.

Very linear as can be expected from a DHT. Let's have a close look at the tube itself:

The tube came well packed in a Telefunken box with a data sheet:

Some more views of the tube:

The box:

More pics of the tube:

Scans of the sheets which were included:

The electrodes are mounted horizontally directly under the top of the glass dome which is covered with getter. Due to the low power filament no glow is visible when the tube is turned on. Shining light into the tube from the bottom reveals a bit of the internal structure:

Due to the scarcity of this tube and since it does not belong to me no dissection photos. Sorry!

Here we have a Marconi R.A. 408 /14. I did not find any data about this specific tube but the naming is similar to the A408 so it is probably an equivalent or very similar. Also since the filament spec is printed on the tube this makes it a safe bet.

And a measurement on the curve tracer shows plate curves which are almost identical to the RE084:

The box:

This tube has some kind of seal above the base. Probably from the finance ministry since tubes had a special tax on them in Italy:

As with the Telefunken tube the electrode system is hidden under the getter.

I hope you enjoyed the last tube presentation for this year. And thanks to Josef for providing the samples.

Best regards