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Assembling together a vacuum tube stereo system

Some helpful hint

One of the visitors to my vacuum tube web site commented that I have a "healthy passion" for vacuum tubes. Considering how much I love music, it seems only natural to use the technology which most faithfully and realistically reproduces sounds and music. Enter vacuum tubes.

I listen to all my music on a stereo system which is 100% vacuum tubes. Archaic you say. Not really. It is true that solid state predominates and almost monopolizes the hi-fi market. However, there is a small, but steadily growing, number of vacuum tube fans who love to listen to music exclusively on vacuum tube stereo systems.

Vacuum tubes are enjoying a renaissance. This renaissance is well deserved. They should have never gone out of favor to begin with. Over the last few years, people are starting to realize the sonic advantages of vacuum tubes over solid state. I will not go into the differences here - that could be the basis of a future article. Suffice it to say, that vacuum tubes blow solid state out of the water. Until you have heard a vacuum tube stereo system, you have not heard anything!

So how does one actually put together a vacuum tube stereo system, typically for home use. There is no shortage of new vacuum tube stereo components to choose from. Some companies that in the past manufactured vacuum tube stereo components (tuners, pre-amps, and amps) are now in business again, although possibly under different owners. In addition, new companies are on the market with products of their own.

Of course, there is a huge amount of used components available. Products which were manufactured in the 1950's and 60's are easily available. Names like Dynaco, Marantz, Macintosh, Sherwood, and Heathkit are all ready to be purchased by the tube connoisseur.

From both a cost point of view and a performance basis, I would suggest utilizing used components for the vacuum tube stereo system, as opposed to new ones.
Although these components may be as old as 40 to 50 years, if you obtain one in excellent to mint condition, and one that is currently working, then you should have little problems with it.
No doubt some will need a overhaul such as new filter capacitors, new tubes, and new capacitors and resistors which are out of tolerance. If you are lucky, you can get one which works very well from the outset.

My goal in assembling a vacuum tube stereo system for myself was to re-create a system from the 1950's and 1960's. I wanted the 50's and 60's sound from the system. When I put on a Beatles' album from the 60's, I wanted that album to sound just like it did in that decade.
No solid state - no digital. Only vacuum tube and all analog. Albums from the 50's and 60's were mastered and cut on vacuum tube equipment. Hence, playback should be on the very same type of equipment to achieve that authentic 500s and 60's sound.

It made sense that in order to achieve this goal, components from 50's and 60's would have to be used. I set a realistic budget, and therefore only certain components could be selected. You don't have to spend a fortune to achieve great sound. This is a common misconception. There is not a linear relationship between cost and quality of sound.

A stereo system consists of two basic components - (1) preamplifier, and (2) amplifier. These components may be separate and connected by cables, or they may be combined into one unit called an integrated amplifier. Separate components is preferable for more pure sound.

I decided to base the pre-amplifier and amplifier on Dynaco products. Dynaco products were constructed of high quality parts, and were not expensive. Circuitry was simple, but at the same time elegant.
In sound reproduction, the simpler the signal path, the better the sound. This simplicity of Dynaco design allowed excellent sound to be obtain with a minimum of electronic parts.

For the preamp, I chose the Dynaco PAS 3. This unit is built tough and has excellent sonic attributes. I believe that the PAS 3 sounds as good, if not better, than units costing $1,000 to $2,000. The beauty of a PAS 3 is that it can be purchased for only $100-$200 depending on condition. All values are quoted in US dollars.

The heart of the PAS 3 is the 12AX7 tubes. Four of these are used (two for each channel). The OEM 12AX7 tubes supplied by Dynaco for the PAS 3 were Telefunken.
The sound of these tubes is legendary. Telefunken 12AX7 tubes are famous for their sweet smooth sound.
The Telefunken 12AX7 excels in the midrange - for example, the human voice. So, songs come through as very melodic when played through these tubes.

The PAS 3 uses a 12X4 rectifier, and a selenium rectifier. For those who believe in tube rectification versus solid state rectification, the use of the 12X4 tube will be a welcome technical detail.
The downside of using a selenium rectifier is that as it ages, it is prone to breakdown. You can tell that it is not working when you get a rotten egg smell (sulfur and selenium are very similar chemical elements). However, my PAS 3, which was purchased used, is working just fine even after over 3,000 hours of use.

On a hot summer day, the PAS 3 gets fairly warm to the touch. The heat does not seem to bother it. Admittedly, the unit has a small enclosure, and between the five tubes, the selenium rectifier, and the power transformer, a definite amount of heat is generated.

One unique feature which the PAS 3 has is a separate bass and treble control for each channel (a total of four controls). This is not found on modern units.
The advantage of this feature is that it allows you to fine tune the frequency response for each channel separately. In addition, the PAS 3 has a stereo expander control which adjusts channel separation.

It seemed natural to match the PAS 3 with the Dynaco ST-70 amplifier. These components were designed for each other and work best as a team. I was fortunate to find a used original ST-70 of very early production. The output transformers on these early units were hand wound in the USA.

The Dynaco ST-70 is a spectacular amplifier which rivals much more expensive tube amplifiers of that era (1950s-1960s). It sounds as good as other brands costing as much as $1,000 to $3,000, and yet can be purchased used for only $250 to $450 US dollars. A 1964 Dynaco brochure states that the ST-70 has "firm, perfectly defined bass, and smooth, natural highs. Absolute stability provides a transparency which delineates the most subtle orchestral nuances".
The electronic circuitry of the ST-70 is very conservative which leads to long life of both the unit itself and the output tubes. The Dynaco brochure states that "the Stereo70 is noteworthy for ultra-conservative operation : output tubes operated at only 65% of capacity, and filter capacitors at less than 85% of rated voltage".

As a companion to the original Dynaco ST-70, I also located a new Dynaco ST-70 Series II amplifier. This unit is an updated version of the original ST-70 (see my previous articles in TNT Audio about the similarities and differences between the original Dynaco ST-70 and the Series II).
Both units can be used interchangeably with the PAS 3 preamp. Suffice it to say here, that the major differences between the two versions of the ST-70 are 1) that the original uses tube rectification, and the Series II uses solid state rectification, 2) the Series II has a larger power transformer, and 3) the Series II has a larger capacitance in its power supply.

Both versions of the ST-70 generate a lot of heat, especially when one considers that the amplifiers are Class A up to 25 watts per channel (and then class AB to 35 watts per channel). So in Class A the amplifier is running at full tilt - this uses a lot of current, and subsequently generates a lot of heat.

For the tuner in the stereo system, I chose the Sherwood S-3000 V. This component was manufactured by Sherwood Electronic Laboratories in Chicago in the 1960s. Sherwood produced an entire line of hi-fi components. The S-3000 V is a 9 tube FM only tuner. It weighs 19 pounds.
The amazing things about this tuner are the fantastic sound, and the physical length of the slide rule scale (21.5 cm). The sound is probably as good as it gets for a FM tuner. The very long slide rule scale makes tuning stations, especially weak ones, very easy. As a testimony to the way components were manufactured in the old days, the slide rule scale is made of glass (not plastic)!

The entire vacuum tube stereo system is 100% vacuum tube (except for solid state rectification where indicated). It feeds into a pair of floor standing Paradigm 11se Mk II speakers. Complementing the system is a Parasound C/DX-88 CD player, and a Dual CS 505-3 belt drive turntable.

The key advantage of a vacuum tube stereo system compared to a solid state one, is that I can listen to the vacuum tube system for hours and hours at high volume without any fatigue. This is due to the predominance of second order harmonics in the tube system compared to third order harmonics in the solid state system.
Second order harmonics are much softer in nature. In contrast, third order harmonics are harder in nature.

I have not used my solid state receiver in years. I just keep it as back up. The vacuum tube system is played everyday for many hours. I have only had to replace one tube - a 6BS8 in the tuner. That track record is after over 3,000 hours of use!
So despite what may be said, vacuum tube technology is very reliable. Especially when mated with vinyl records, tubes are king!

© Copyright 2000 Harvey A. Kader - http://www.tnt-audio.com

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