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Friday, April 26, 2019

The Digital to Analog Converter


The DAC is finished.

Above the chassis which houses the DAC and tube output stage. Power supplies are separate and split into two chassis one for the analog tube output stage and one for the digital part.

The digital power supply chassis (bottom) contains two completely separate PSUs one for the receiver board and one for the DAC board.

So we have a 3 chassis system:

The DAC can be connected to a CD transport via the Coax input or to a PC/laptop or server via USB.

The analog output section is transformer coupled and offers balanced and SE outputs. This DAC can use 10Y or 801a tubes. Here equipped with ELROG ER801A. The DAC can also be built for other output tubes.

The one shown will represent the entry level model with single ended output stage and copper transformers. A silver version is also planned and an ultimate differential all silver version. I am building a few initial sets. If you are interested in a DAC from me, special pricing will be offered if you preorder one of the first sets. Email me for more info

Best regards


Tuesday, April 23, 2019

Tube of the Month : The UX199


This month we are looking at a very old tube type which was introduced almost a century ago, the UX199.

The UX199 was developed as a detector and amplifier tube for radio receivers. It was among the first commercially produced vacuum tubes.

The UX199 was released in 1925 as the successor of the UV199 which was introduced in 1922. The difference being only the base. While the UX199 has a UX4 base, the UV199 had the UV4 base which used much shorter, stubby pins. The UV199 was the first commercial tube to use thoriated tungsten filaments, the properties of which were discovered by accident. In 1920 a production run of pure tungsten filament UV201 tubes was contaminated with thorium. The engineers realised that these tubes performed better and thus investigated and developed the thoriated tungsten filament. The UX-199 and UV-199 had a very efficient filament which only consumed 60mA at 3 to 3.3V. Thus perfectly suited for portable or battery powered radio sets. By 1931 these tubes were already discontinued. The UX199 was positioned as a similar tube as the UX201A but with more efficient filament. It has an amplification factor of 6.6 and a plate resistance of about 15kOhms, which results in a measly 425 micromhos. About half the transconductance of the UX201A. For the complete technical data refer to the Cunningham data sheet. The data sheet does not show any plate curves, so I took a set of curves from an actual tube:

Seems like a nice tube wich could be used to create a special vintage like touch to the sound. I never actually used any UX199 and also never bought many of them. Lets have a look at the few samples in my stock.

Starting with a RCA Radiotron UX199.

The tube has a very slim, straight sided glass envelope which has about the same diameter as the base. A rather modern look for a tube from that era.

The glass is entirely covered with getter in the inside. Another RCA, this time still in its beautiful box:

The tube is well padded for optimum protection:

This one has a sticker with a hand written note when it was tested.

More photos of the box:

Next we have a sample of the UV199 made by RCA:

The UV base with the short pins had issues with making good contact and therefore was replaced by the longer pin base.

This tube is of later manufacture and came in this more modern RCA box:

Probably made for replacement purposes after the tube numbers got reduced to the last two digits.

The last sample I have to show was made by DeForest Radio Co:

Those vintage tube boxes are simply gorgeous.

Inside similar padding as in the RCA box:

Due to the low filament power not much of a glow visible and in the RCA mostly obstructed by the getter:

The DeForest reveals a bit more and here we see the cylindrical arrangement of grid and plate around the single filament string:

I hope you enjoyed the presentation of this vintage tube. 

Best regards


Saturday, April 20, 2019

The Silver Differential 46 Mono Amplifiers - Part 2


In the announcement of this years participation to the High End in Munich I mentioned that I will cover some of the amps which will be used for demo.

One of the amps will be the new finished all silver differential power amps. Initial construction steps of these have been shown in part 1.

A pair of 46 is driven by another pair of 46 using all silver transformers and plate chokes. 7 silver wound pieces in each mono block.

Each amp weighs over 40kg with a big part of that being silver. Admittedly that is a lot of weight for some 3.5W output power. But worth it. These are the best 46 amps I built so far.

Come to the Munich High End to room F231e to listen to these

Best regards