2A3 - 300B - 45 - 845

The attraction carried on by the great audio triodes with direct heating of the filament is growing more and more.

Now, it is not possible to be ignorant of their qualities without being out of the High Fidelity world. Actually , 4 types are readily available covering virtually all requirements. They are the 2A3 , the 300B, the 45 and the high power 845.

Understand that they were created long time ago for the first talking movies , we must respect them in order to arrive at the musical perfection they are able to provide.  Those triodes being tyrannical with the technicians who are faced in designing an amplifier. There should be no compromise . The design around the tube must be perfect or some default will emerge and deteriorate the listening result, mainly by hum, and /or a deficiency of the bass and treble.  If the cost needs to be lowered it is easier to use the symmetrical mounting ( Push Pull ) which does not require the same care.

The 45 is a special version designed for North America.  The 2008 model has the special selectable AC/DC filament switch, hum reduction pots, and a preamp/gain control which can be bypassed.



2300B - 300B

2300B - 300B 


2300B - 2A3 



2300B - 45 




Triode Spirit Design Principles

The number one problem which must be tackeled is Hum.   Generally they come from the power supply circuits. Each model of the TRIODE SPIRIT line has a regulated power supply.  It provides a constant voltage in all circumstances on all the amplifier stages. The regulated power supply which is already expensive to realize for the 2A3, 45 and 300B models, becomes a real technical challenge for the 845 as it needs a plate voltage of 820 Volts.

This power supply is in addition intricate to design ( see the article in Sound Practices issue 14 ) and it needs the use of 3 tubes ( in the 2A3, 45, 300B amplifiers) or 4 tubes ( in the 845 amplifier ) to work properly.

Response in low frequencies

A detractor of Mono Triode amplifiers will say : " Yes it's musical but there is no bass. This comment might be true if the amplifier is made to save money with a cheaply built output transformer .

The size and consequently the weight of the transformer is decisive because it conditions the value of the primary inductance which must be as high as possible. ( See the technical note on this subject ) The output transformer as a vital part must according be designed at its best , taking in account the finest technology, while respecting the rules of art.

Another challenge, the treble response.

Generally, the major problem comes from the dynamic input capacitance ( about 50 to 100pF ) of the power triode. This requires a preamplifier stage with low output impedance - practically a power stage - able to provide current in high frequencies . In a sort forcing the output triode to accept the modulation against its will .

To obtain this, we designed a completely innovative input stage, it consists of 2 tubes put in a configuration of " ultra linear mu follower pentode " ( please accept our apologies, but we could not find another name ). This stage presents the double benefit to have a very low output impedance ( about 100 Ohms ) and a negligible distortion.

This feature is valuable because it passes on an ultimate profit: it does not change the original sound of the output triode by an
inopportune compensation effect. This feature does not alter the special sound of each triode and allows - possibly for the first time - to make auditory comparisons really significant between tubes of different origin.

For this last reason, we named this line of amplifiers "TRIODE SPIRIT" hopping to show the devoted care, the quasi religious character of our reverence for the great triodes of the past.


At the origins of low frequency tube amplifiers, the mounting of a single tube was reserved to devices using simple and cheap materials .
By opposition the symmetrical mounting was meaning of perfection and therefore found only on performing and expensive equipment. It is interesting to note that this tendency is now quite opposite. This surprising result has various reasons , two of them are described below.

1 - Poetical reasons
During the 70's Japanese enthusiasts - passionate of music and technique - have discovered the qualities of an old "WESTERN ELECTRIC" apparatus. This talking picture amplifier designed for small movie theaters was fitted in its output stage with a single tube 300B (WE 91A).
The amplifier was not perfect but gave surprising musical results. The dynamics coming from this amplifier seems more potent than its modest rated power let suppose. Working on the matter by improving the power supply to reduce the " hum "and using a bigger output transformer, our Japanese enthusiasts gave birth to a new range of High Fidelity single tube amplifier. We have to recognize that this amazing result was ,it seems,a real snook to the technical world.

2 - Technical reasons
As we know, technical explanations given their value to the musical results have never been approached .
For this reason, I ask the reader to take my conclusions only as assumptions.
First, we have to evoke a specific aspect: The dynamics . Let us suppose that a musical ( sinuso‹dal) signal modulates the grid of a tube in a positive direction: the plate current will increase and become maximum. This current flowing in the primary of an output transformer creates a maximum instant voltage at the secondary corresponding to a maximum instant power.
When the signal modulates the grid of a tube in a negative direction: the plate current will decrease and arrive to break when the grid is at the cut-off point, the current inside the primary of the output transformer ,then ,becomes zero. At the secondary we recover a maximum instantaneous power, there is no more current.

Where is this power coming from?

Of course there is the Lenz law which " works " by providing a magnetic field opposed to the disappearance of the current. This natural effect works well as much as the primary inductance of the output transformer is enough to store the energy; and there is the fundamental importance of the design of a generously sized output transformer if we wish to have a good reproduction of the low frequencies.

The energy stored in the primary is:

For example in a 300B stage, the idle current is generally 75mA when a good transformer has a 20 Henrys primary inductance.
In this case :

Let us calculate the distribution of this power according to the frequency we have to reproduce:
At 20Hz the time necessary for the inductance to give back energy is 0,025 seconds.
During this time the inductance is able to give back a power of :

It is not much and explains the fall of the power in the bass extremities.
At 100Hz the time of return is 0,005 seconds. The corresponding available power is:

This power is widely appropriate and the respone at 100Hz is practically perfect .
The same calculation for the frequency 1000Hz reveals now why Mono Triodes amplifiers have a musical power reserve so amazing. At 1000Hz the time of restitution is 0,005 seconds that gives a disposable power of:

Here we ought to compare with what happens in a push pull amplifier, it is easy because of their principle . The electricity stocked in the primary of the output transformer is always non-existent, and therefore the profitable phenomenon described above is not present.

In the future, I will comment about the reserves written at the beginning of this technical note. My assumptions are not yet confirmed by well-know scientific studies and I am waiting for the confirmation of a mathematician .

Last year, I added to my "Triode Spirit" amplifiers range a "luxe" version of the 845 model. The great success of that presentation, more attractive, in spite of its high price, leaded me to apply the same formula to my other amplifiers of the "'Triode Spirit" range :

It is now possible to obtain these models in "luxe" version and a middle version with bright stainless steel chassis is also available for 300B and 2A3 amplifiers.

Please notice that the 2A3 "luxe" model is equiped the same way as the 300B, with the same important transformers. 

Moreover, all the technical aspects of the models are still the same and musical performances have not been modified by these aesthetic improvements.

 Jean Constant Verdier


About the different qualities of finish.

When the amplifiers of the "Triode Spirit" series were proposed for sale there was only one finish quality called "STandard" and consisted of a chassis covered by a a lacquered paint loaded with bronze powder.

Now the offer has evolved and the 2A3 and 300B "Triode Family" amplifiers are available in 3 different finish aspects.
1) The "Standard Models" (described above)
2) The "Black shadow" Models : the chassis are made in mirror polished stainless steel.
3) The "Luxe" Models  are made on a brushed anodic and aluminium chassis that is Champagne colored of 10 mm thick.

The 845 Model is proposed only in the "Luxe" version because we noticed that the standard version is quite as expensive as the "Luxe Version".


Power Requirement230 V 50 Hz  /  117 V 60 Hz or Request
Power Consumption300 Watts
Output Power20 Watts
Input Sensitivity400 mV
Total Harmonic Distortion0.5 %
Vacuum tube used1x845 - 2x5R4 - 2x6550 - 2xEL84 - 2xEF184.6EJ7
Weight (Luxe)30 Kg


Power Requirement230 V 50 Hz  /  117 V 60 Hz or Request
Power Consumption300 Watts
Output Power2x6 Watts
Input Sensitivity400 mV
Total Harmonic Distortion0.5 %
Vacuum tube used2x300B - 2x5U4 - 2x6080 - 5xEF184.6EJ7
   Standard OR Black Shadow25 Kg
   Luxe30 Kg


TRIODE SPIRIT 2A3 $ 6000 USD (Standard) 
Power Requirement230 V 50 Hz  /  117 V 60 Hz or Request
Power Consumption200 Watts
Output Power2x3 Watts
Input Sensitivity400 mV
Total Harmonic Distortion0.5 %
Vacuum tube used2x2A3 - 2xGZ34 - 2x6Y6 - 5xEF184.6EJ7
   Standard OR Mirror15 Kg
   Luxe30 Kg


TRIODE SPIRIT 45 $ 5900 USD (Standard) 
Power Requirement230 V 50 Hz  /  117 V 60 Hz or Request
Power Consumption200 Watts
Output Power2x2 Watts
Input Sensitivity400 mV
Total Harmonic Distortion0.5 %
Vacuum tube used2x45 - 2xGZ34 - 2x6Y6 - 5xEF184.6EJ7
   Standard OR Mirror15 Kg
   Luxe30 Kg




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