The "Triode Spirit family"
The famous 300B was always honoured as much as possible on the
range of J.C.Verdier's amplifiers.
The amplifier Triode Spirit 300B Luxe is fitted with 9 tubes used in the following function :
2 X 300B direct heating power
TRIODE SPIRIT 845
The amplifier Triode Spirit 845 luxe is fitted with 9 tubes used in the following fonctions :
1 X 845 Direct heating power triode
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 , 2 types are readily available covering virtually all requirements. They are the 300B and the 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.
Now, let us take a close look at the obstacle we must clear to obtain perfection ( yes it is possible ).
First of all the 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, expensive to realize for the 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 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.
This feature is valuable because it passes on an
ultimate profit: it does not change the original sound of the
output triode by an
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 .
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
Let us calculate the distribution of this power
according to the frequency we have to reproduce:
It is not much and explains the fall of the power
in the bass extremities.
This power is widely appropriate and the respone
at 100Hz is practically perfect .
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 .
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 :
Please notice that the models are equiped with the same important transformers and are made on a brushed anodic and aluminium chassis that is Champagne colored of 10 mm thick.
Moreover, all the technical aspects of the models are still the same and musical performances have not been modified by these aesthetic improvements.
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