UX201a / UX301a Pre-amp by Radu Tarta

Here is a revelation; a DHT preamplifier using the ancient UX201/301a tube. The UX201a (RCA) and UX301a (Cunningham) dates to 1925 and is one of the very first of the triodes. Used in countless early battery radio sets, these tubes were made in the millions and can still be easily found on eBay and with tube merchants, sometimes still packaged in their original cartons; a time capsule to the mid 1920’s.

Like the early type 10 globes, the UX201/301a have the very desirable Thoriated Tungsten filaments (but not the later ST-shaped 01a), which give the tube such a big and detailed sound and make it one of the best sounding triodes ever made. About the only place you see these tubes employed now are in super high end preamplifiers and line stages. Thomas Mayer is a big fan of the tube and has several articles and projects on the 201a on his excellent website, Vinyl Savior. When I found Radu Tarta’s listing for this cool looking little preamplifer I jumped at the chance to own it and was excited to get it into my system. And for good reason, its a nicely made preamplifier with mid-level parts and a lovingly constructed wooden base. Used as a test bed for a few of Radu's projects, the final amp has some additional holes and is slightly Frankensteinien in appearance. I actually do like that, but at some point I'd like to upgrade to one of his more elaborate and polished projects, as I'm a big fan of this one!

Radu’s preamp uses the UX201a to get about 18 db of gain, which turns out to be more than needed for some of the amps I have with super sensitive inputs. It does work fabulously with several of my little triode amps though; and in particular it's a great match to my Sean Casper AD1. Paired with Sean’s amazing work, this little 201a adds another layer of texture and space to an already incredible sounding amplifier. Luckily the AD1 has its own volume control so I can easily A/B test between the preamp and only the onboard volume control, and its quite clear that I prefer the huge and lush UX201a treatment.

How to describe what the little 201a tubes are doing? Romance. Depth. Space. The UX201a and its tungsten filaments open up the program material in very pleasing ways. On small-scale acoustic music, Nora Jones for example, suddenly everyone in the performance is slightly bigger and bolder and everything sounds subtly (and sometimes not so subtly) more realistic. Heavier electronic music takes on new scale and weight. I’ve written on these pages before about program material sounding so real and in the room, and the 201a turns that up to 11. Its definitely not a neutral presentation, and as such will not be for everyone, but I can say that I’m a believer.

There are a few caveats to the UX201a. It's a very microphonic tube, and demands special treatment in the audio chain. Radu built this amp with the tube sockets dampened to reduce vibration, and I’ve added vibrafeet to further isolate the amplifier from its surroundings. Even isolated, with some tubes a slight tap to the top plate sends noise through the signal path and you hear an eerie ping from the tubes. Radu did supply the amplifier with selected tubes that are not prone to this problem, but of course being a tube roller I’ve tried a few varieties now and have settled on the Mello Tron tubes for their tonality even though they are somewhat microphonic. In fact, it sort of seems that the microphonics add to the pleasurable sound in some way. So, it can be finicky, but it's a small price to pay for a big leap forward in sound. I love my Minimax preamplifier, and it is far more versitle (and multi-input), but I think its been sent to the bench for the time being at least. More of Radu Tarta's work can be seen at his website: simple pleasure tube amps. Mr. Tarta makes some superb looking single ended power amps, and I hope to be lucky enough to try one in the future.

This may be a rougher looking top plate, but combined with the wooden case it has great karma and was clearly made with precison and care. Most of Radu's amps are super clean looking with pro-machined top plates, seperate power supplies, etc. and are drop dead gorgeous. One day a fancy 2 chassis version of this preamp is in my future.

Because of the extreme microphonics associated with the UX201a, some sort of isolation is essential with these tubes. Here I'm using foot damers to protect the amplifier from surface shocks. Believe it or not this makes a marked improvement with the UX201a tube.

Tube rectified of course.

The creme de la creme of 1925–1926 audio: Here we have an array of 01a tubes; beginning with the RCA Radiotron UX201a, followed by the DeForest Audion 401a, and finally my personal favorite so far, the UX201a by Mello Tron. What a wonderful name! These are some of the very earliest triodes; and in fact this is among the earliest tube ever marketed by RCA. Apparently the taller base denotes an earlier tube, so the RCA and Mello Tron likely date to '25 or '26. The DeForest tube features a wonderfully artful engraved base. Cool stuff!