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Monday, August 22, 2022

Tube of the Month : The 1625


This months tube is a transmitting beam power amplifier, the 1625.

The 1625 was designed for use as AF amplifier or modulator as well as for RF amplification. Except for the heater it is identical to the 807.

The 1625 has a 7 pin base and a small top cap for the plate connection. It is an indirectly heated tube with a 12.6V heater which consumes 0.45A. It is electrically and mechanically identical to the 807 with the only exception that the latter is heated with 6.3V / 0.9A. While it was intended to be used in Class AB2 configuration where it can deliver up to 120W, I have seen 807s used in singe ended amps and in triode connection as well. I never built anything with these tubes, so cannot share any practical experience but I am sure these are some excellent amplification devices. Since I have some of them in my tube stash I thought I write up a tube of the month post about them. As always let's have a look at the plate curves:

The data sheet also shows the triode connected curves:

Actual curves taken from a tube with the tracer:

These don't look too shabby. Let's have e a look at the tube.

I have some RCA 1625 in the beautiful world map boxes:

Probably the most beautiful tube box ever made.

The tube is wrapped in protective cardboard inside:

Inside the cardboard is some detailed documentation:

Some details of the tube:

More photos of a 1625:

The military designation is VT-136:

The plate obstructs most of the glow when the tube is in operation:

On the bottom part of the grids is visible:

An interesting tube worth considering for an amplifier project if you don't mind the top cap.

Best regards


Sunday, August 7, 2022

Deutsche Elektronenröhren Manufaktur GmbH 6th Anniversary


Today we are celebrating the 6th anniversary of making ELROG tubes at Deutsche Elektronenröhren Manufaktur.

In August 2016 Deutsche Elektronenröhren Manufaktur was founded and acquired all assets and brand rights of Elrog Elektronenröhren GmbH & Co KG. The initial range of ER211, ER845 and ER300B was substantially improved in design and materials and continued to be produced under the new firm. Each year new tubes were introduced and the portfolio is now 18 types strong, of which 14 types are for general sale and 4 are exclusively produced for Thomas Mayer amplifiers.

The latest additions are a molybdenum plate version of the ER801A called ER801A-Mo and a TM801A which captures the sound qualities of a 46 in a tube with 801A specs, similarly to the TM300B. And a molybdenum version of the TM300B, called TM300B-Mo.

Yes, this means there are 4 variants of ELROG 300B tubes now.

And three variants of ELROG 801A tubes:

All these are fully compatible with old production 801A tubes and can be used in applications designed for 10, 10Y, VT15, VT25A, 1602, 801, 801A or VT62.

The new 801A variants have already been tested by some customers. Here are their impressions.

The first used the TM801A in his silver 10Y linestage which drives silver TM300B monoblocks.

These are his impressions:

It feels like whatever the TM magic is, it works very well…:)

It really 3Dimensonalises the sound. To me it’s like a Leica lens compared to other lenses. Leica optics makes the images to be more 3D and buttery. It has enhanced micro-contrast. It’s not romantic, but the perfect balance between sharp and still humane/warm. You can touch the soul of your subject, without being overly analytical and loosing the mystery of you subject. 
Now change Leica with TM and subject with recording…:)

So, now I need another pair for the monoblocks…:)

Next the impressions of a customer who compared the ER801A-Mo and TM801A as driver tubes in his monoblocks which are equipped with TM300B

I listend to both ER801A-Mo and TM801A as driver tube in 300B SE power amps with TM300B as output tube.
The power amps are directly driven from a DCS DA-Converter with Aurender music server. No vinyl all digital.

The short summary of my impression is easy: The Mo is the refined and optimised variant of the already high resolution ‘regular ER801A’ while the TM801A is the ideal partner to the outstanding sound quality of the TM300B.

More in depth description: The Mo not only does everything a bit better that the 'regular tube’ but its convincing resolution, openness and rock solid presentation is immediately apparent…and this without any aggressiveness. It impressively suits listeners with a preference for resolution and detail.
The character of the TM801A is more subtle she demands full attention to be able to enjoy its extraordinary finesse and underlines the quality of the TM300B perfectly.
The comparison to a very good wine is not far fetched. In both cases connaisseurs and hedonists get a treat and are rewarded.

Both the TM and Mo offer for different preferences the optimum especially in combination with the TM300B. The developers of these tubes must have extraordinary knowledge and experience.

This is my translations of his comments here is the original version for the german readers:

Sowohl die Elrog 801A Mo als auch die Elrog TM 801A wurden als Eingangsröhren
in Kombi mit Elrog TM 300B in den Endstufen 300SE gehört. Die Endstufen wurden
direkt von einem DCS Wandler angesteuert; als Quelle diente ein Aurender Musikserver -
also kein Vinyl, sondern alles Digital.
Die Kurzfassung meiner Wahrnehmung klingt ziemlich simpel. Die Mo ist die verfeinerte,
optimierte Variante der ohnehin schon auflösungsstarken „normalen Elrog 801A“, während
die TM 801A die kongeniale Partnerin zu den außergewöhnlichen klanglichen Qualitäten
der TM 300 B erscheint!
Im Einzelnen macht die Mo nicht nur etwa alles einen Tick besser als die „Normale“,
sondern ihre bestechende Auflösung, Offenheit und felsenfeste Darstellung springt
sofort ins Ohr…und zwar ohne jegliche Aggressivität. Damit spricht sie Hörer mit Vorliebe für Auflösung und Detailwiedergabe in beeindruckender Weise an!
Der Charakter der TM ist da subtiler. Sie fordert sozusagen volle Aufmerksamkeit, damit
man ihre wirklich außergewöhnliche Feinheit und ihren Klangfarbenreichtum genießen
kann…das hat fast unheimliche Finesse und unterstreicht und unterstützt die Qualität
der TM 300B perfekt! Der Vergleich mit einem besonders guten Wein ist vielleicht
gar nicht so weit hergeholt…in beiden Fällen werden Kenner und Genießer angesprochen
und belohnt!
Beide, TM und Mo, bieten für die jeweils klanglichen Vorlieben vermutlich das Optimum
ab ! Und das insbesondere in Verbindung mit der TM 300B. Die Entwickler dieser Röhren müssen über außerordentliche Kenntnisse und Erfahrung verfügen…..
Gratulation und Respekt!

More reviews of the TM801A will follow. Stay tuned!

Above our 'big boys'. Below our rectifiers:

Our triode with the least demand is the ER50:

This tube shows how tricky it is to decide about new tube developments. We had many requests to bring out this tube but actual demand turned out to be too low for continuous production. I occasionally get asked about the 2A3. We did contemplate to bring an ER2A3 to market and even developed some working prototypes:

But the thoriated tungsten filaments used have a different thermal behaviour than oxide coated filament which results in more residual hum when AC heated. Since the vast majority of 2A3 amps are AC heated and typically used with high efficiency speakers we decided against selling these. Thoriated tungsten filaments are giving all our tubes their signature sound and we would not want to bring out an oxide coated filament 2A3 like all others on the market. Restricting their use in DC heated amps would reduce their demand to less than that of the 50. So sorry no ELROG ER2A3.

But there are already ideas for other new types to introduce.

I'd like to thank the staff of Deutsche Elektronenröhren Manufaktur GmbH for their continuous passion and hard work and to all users of ELROG tubes. Without you audio tube production in Germany would not be alive.

Best regards