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Thursday, October 27, 2016

Tube of the Month : The 800


This months tube is a directly heated transmitting triode, from the RCA 800 series. It is actually the very first tube in that series, the 800 itself.

I have never done anything with that tube and most likely never will. But it is an interesting triode nonetheless and certainly usable for audio applications.

Like most transmitting triodes, it uses a thoriated tungsten filament. In this case with 7.5V and 3.1A. So rather hefty requirements not far off from the 211 or 845. The base is UX4 but only 2 of the pins are used. The filament is supplied through the base. There are two caps on top of the tube which give it a very distinctive look. One is for the plate connection and the other for the grid. This arrangement keeps inter electrode capacitances low which helps for RF applications. The tubes was intended for both RF and audio frequencies. The data sheet lists operating conditions for use as Class AB power amplifier and modulator and for Class C RF power amplifier service. There is a sample circuit of a PP amp with two 800 as output tubes driven by a push pull pair of 45s. The tube was mainly designed for grid current operation but like most such tubes could be used in Class A1 as well.
However no parameters are given in the data sheet for Class A1 operation so these would need to be characterised. I haven't looked at that in detail but probably an output transformer with rather high primary impedance would be needed. Output power in SE Class A1 is probably around 10W. But then why not use this tube as intended and drive it in Class A2 with a suitable driver or even AB as suggested in the data sheet for a healthy 100W of thoriated tungsten directly heated output power. An amp with 2 or even 4 of these with their cool cap connections would certainly look great. May be some day I will find the time to look into this in more detail. Here a quick shot of the plate curves in Class A1 region which look as good as you can expect from a directly heated triode:

Some photos of the few 800 tubes I have:

A nice sample in big RCA box. The tube is padded in soft card board inside:

Some more photos:

The base:

Here the grid is visible:

Details of the box:

This tube also carries the military designation VT-64.

Another 800:

This is a RCA de Forest.

Close up of the base:

Grey coated plate on this one:

The top:

Here the connections from the caps to the grid (right) and plate (left) can be seen:

Closeup of the grid connection:

Let's have a look at the tube in operation:

The filament gives of a bright almost white glow. When turning down the filament voltage some details become visible:

Close Up:

The next photo gives a better view to the filament:

A close up shows that the filament is actually a spiral:

Another view:

Turning down the filament voltage further makes it easier to see more details:

A very interesting filament structure which allows a nice cylindrical arrangement of all electrodes.

A great tube! If you have some actual experience with this triode in an audio amp, let me know!

Best regards


Saturday, October 22, 2016

Music : Yello, Toy


Being a fan of Yello since the 1980ies, I had to get their new album as soon as it was out. It is called Toy, and deserves a quick review.

It took them about seven years to release a new album after the last one 'Touch' which came out in 2009. It is Yello's 13th album. Being in the music business since the late 1970ies can they keep up with the high expectations their fan base has towards a new album?

Most Yello albums are both very different from the previous releases yet carry the typical sound signature of the Swiss duo which is easily recognised. The first track of Toy is very unlike Yello. It reminded me of typical synth music from the 1970ies. It sounds a lot like Jean Michel Jarre. Which was a funny coincidence because just a few days before I pulled out Jarre's Oxygene and blasted through both sides. I wanted to see how some old electronic music sounds through the ultimate phono stage and ultimate line preamp (it's amazing what this combo picks out of such old records). So it seems Yello paid an homage to Jarre with their intro called 'Frautonium'. They are also ending the album with such a track.

All in all the music on Toy is rather slow and mostly dominated by Dieter Meier's typical narrative style of singing. And of course Boris Blank did his part with his amazing sound creations and samples. As on many other albums there are guest musicians. Most notably Mahlia who sings in some newly interpreted titles from her album 'Convergence' which was produced by Boris Blank.

Yello reuses a lot of material from their own previous work and also from Boris Blank's Electrified. At first listen this can appear as some lazy rehash of old material, but it all has a fresh touch and does not disappoint. They not only pay a homage to Jarre but also to themselves.

The track 'Star Light' also reminded my of some song I new. After a while I realised which one it was. The base line, guitar and melody seem to be straight of the late 1990 hit 'Bakerman' by Laid Back.

The title 'Magma' and 'Toy Square' on the last side carry many sound elements as found on the Yello album 'The Eye'.

Did they overdo the sampling and quotes from other albums? Laziness or homages? I go for the latter since the album is great. May be not one of their best releases but special nonetheless.

Recording quality is superb as is usual with Yello albums, and it is available on vinyl. My copy has some surface noise on some tracks but otherwise appears to be well pressed. Maybe the spare copy I got is a bit better.

If you like Yello, get the vinyl and savor it!

Best regards


Sunday, October 16, 2016

The Ultimate Phono Stage - Part 4


As promised in part 3 about this phono preamp, here some more photos and some sound impressions.

I have been living with this unit for some time now. This helps to get a good feel for it's capabilities and is better than writing in the first excitement when a newly finished device is used for the first time. Especially when only the finest parts and tubes are used as in this one, there is quite some expectation bias.

So can the use of silver transformers really improve upon the already magnificently sounding copper version?

Yes, absolutely! The improvements are similar as heard between the copper and silver versions of the line stage. Especially in combination with the matching ultimate line stage, this is a revelation.

Please forgive the ranting and keep in mind I am building these preamps for a living. So judge my impressions accordingly. Whoever is interested can have a listen to this at my place to get his own impression.

The total absence of capacitors in the signal loops enables these to dig out details from the recordings which have not been apparent before. Tiniest details in the background become visible. And this without distracting from the musical flow. It just adds to the ambience and realism of the presentation.  Voices are simply life like. The nuances and especially decay of each tone is extremely well articulated. A curious side effect: I suddenly also heard flaws in some recordings which I was not aware of before. Like pre echoes from the master tape. Such things are audible in any good system, but I am hearing more of these things now than before. Also on some tracks I heard a slight hum which first disturbed me because I thought something is wrong in the system, only to realise that it was on the recording and it faded out at the end of the track. Now this might seem as a disadvantage, but once realised what it is it didn't spoil the enjoyment. The beauty of the recording is still there, even if it is a mediocre one. This combination of phono stage and line stage is brutally honest.

There is simply more of everything and the records are even more joy to listen to than before. Bass tones are more defined and even the lowest bass notes reveal all the subtle details in the structure of the overtones. Many many shades of dark brown, grey and dark blue, never dipping into an artificial blackness. Just how I like it.

Enough of the ranting. This does not make the copper version a worse performer than it was before, or the single ended variants. They are all fine units and I can happily live with them even after I heard this all silver combination.

Here a view of the back side:

XLR and RCA in and outputs for maximum flexibility. Switches for selecting in and output modes.

Best regards