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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


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