Mythical 300B Power Amplifier

The 60th anniversary of the company is the perfect opportunity to introduce these new amplifiers. The 300B tube is a symbol of the timelessness of certain inventions in the audio domain, like the self-contained portable Nagra of 1951 that revolutionised location sound recording, which in today’s version remains a worldwide reference.

The best technology for the 300B
Nagra’s idea for the 300i and 300p amplifiers is to place the most up-to-date technology around the 300B tube, so as to draw the very best characteristics of these mythical tubes: such as their linearity, low distortion (still better than power transistors available today) and their exceptional harmonic spectrum.

Nagra engineering team has put the characteristics of electronic behaviour at the centre of the specifications for the 300i and 300p. To be certain of this, they opted for a concept of circuit purity, while maintaining elements of comfort and security, expected in modern equipment. They chose a conventional approach wherever possible yet applied the most evolutionary techniques wherever an improvement in the audio could be achieved.

20 Watts per channel
In power terms, Nagra opted for a circuit topology enabling a realistic power to be provided by the 300Bs to comfortably drive high or medium output speakers, popular in today’s market place. They use a polarized push-pull class A configuration giving 20 Watts rms per channel output power. The units are equipped with in-house designed and wound transformers – crucial components in such equipment. They enable the bandwidth to be exploited to a maximum, especially where low frequencies are concerned. The absence of any feed-back on the final amplification stage gives it a remarkable stability. All load types can be connected without any risk of oscillation.

Engineering elegance
Nagra engineers have put the severity of the electronic precision in the centre of the

Excellent handling of the entire frequency response
The reproductive neutrality was an objective of utmost importance. The 300B is renowned for its musicality, the delicacy of its medium and the three dimensional presence it gives to its interpretations. The Nagra 300i and 300p are not only references to these criteria but also push the limits currently achieved by this type of tube in terms of low and ultra-low frequencies.
      
Silent and stable operation
The silent operation is precisely a point which the engineers focused upon, as, on this front, directly heated triodes are delicate to implement. By design, they have a tendency to amplify noise in the power supply, particularly around the filament heater frequency. The powering circuits were therefore designed to supply extremely clean, and perfectly stabilised, voltages. In addition, the selection and dimensions of the components, both active and passive, was made in respect of the most stringent noise requirements.

The overall measurements on the supplies and the configuration of the circuits enabled the natural tendency of these triodes to oscillate to be radically reduced, through the grid-anode coupling capacity. The absence of all feedback at the final stage gives this amplifier remarkable stability. All types of loads can be connected without risk of oscillation.

Shock absorber plates
The integrated Nagra 300i and the 300p are delivered with a set of vibration absorbing plates Nagra VFS.

These solid aluminium plates are fitted with special Alpha-gel® feet specially designed to isolate the electronics they support from vibration. They are specially recommended for tube equipment which is more susceptible to such disturbances.

The vibration-absorbing feature is completed by four conical feet fitted to the box itself. These feet are made from Arcap® with Delrin® resin points which lodge precisely in the machined dips of the upper plate.