What's New with Valve Amplifiers? - Rapallo New Zealand :: Home Theatre & Hifi | Design & Installation
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Rapallo | PrimaLuna Valve Close-up

PrimaLuna just released their Evolution series of vacuum tube amplifiers and components. Including a brand new tube-powered stand alone DAC. We want to write-up a refresher on tube amps, why audiophiles love them, and how they work. We had a question last week from someone about the new features in PrimaLuna’s Evolution series compared to the DiaLogue and Prologue series, so we thought we would explain all the changes PrimaLuna has made.

Before we get into the changes, here is a brief outline on Vacuum Tubes.





About Valve Amplifiers

A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. This type of amplification technology was widely replaced by solid state amplifiers in the 60’s, but are still being used in guitar amplifiers and HiFi stereo amps for their unique sound signature.


In a HiFi amplifier the most comon vacuum tube technology that is used is called a triode. As the name indicates, the triode valve or triode vacuum tube uses three electrodes, the cathode and anode as in the diode, and a third electrode is called a grid placed between the anode and the cathode.

Rapallo | Triode Vacuum Tube


The triode vacuum tube takes the basic concept of the diode and moves it onto another stage significantly. A third electrode called a control grid is placed between the cathode and anode. By applying a potential to the grid, it is possible to repel or attract the electrons being emitted from the cathode and in this way affect the flow between cathode and anode of the triode vacuum tube. Simply put, the platinum grid is the amplifier’s input, and cathode plate circuit is the output.



Ultra-linear electronic circuits are those used to couple a tetrode or pentode vacuum-tube (also called “electron-valve”) to a loudspeaker. A pentode or tetrode vacuum-tube configured as a common-cathode amplifier (where the output signal appears on the plate) may be operated as:

  • a pentode or tetrode, in which the screen-grid is connected to a stable DC voltage so there are no signal variations on the screen-grid (i.e. the screen-grid has 0% of the plate’s output signal impressed on it), or
  • a triode, in which the screen-grid is connected to the plate (i.e. the screen-grid has 100% of the plate’s output signal voltage impressed on it), or
  • a blend of triode and pentode, in which the screen-grid has a percentage (between 0% and 100%) of the plate’s output signal impressed on it. This is the basis of the distributed load circuit, and is usually achieved by incorporating a suitable “tap” on the primary winding of the output transformer that the vacuum-tube (valve) is connected to.


Why do people love Tubes?

The simple answer is that valve amps introduce euphonic distortions, which is a subtle sound signature that is audible to musicians and music lovers (but not exclusive to these people of course!). You see a lot of high-end guitar and bass amplifiers with vacuum tubes inside the amp-head stage.

There are many words and adjectives people use to describe the sound of valve amplifiers including, warm, soft, rich, smooth and dynamic.

Well designed tube amplifiers have simpler circuits and smaller number of components that provide a purer signal path and consequently more truthful signal handling. This is because fewer components provide for fewer elements in a circuit to degrade the signal, distort and muddle the sound. Tubes are voltage amplifiers as opposed to transistors which are current amplification devices. As a consequence, tubes are a more linear amplification technology, requiring less overall negative feedback to make the circuit linear. Negative feedback re-injects a sample of the amplifier’s output signal back into the input, 180 degrees out of phase, in an attempt to reduce amplifier non-linearity and distortion.

The higher working voltages present in tube amplifiers generally allow for wider voltage swings and better signal headroom before entering into overload territory. Higher working voltages yield higher audible energy storage* with lower value capacitors. ~ 500 volts working voltage in a tube amplifier approximate about ~ 80 volts in a transistor circuit. This is most likely why many listeners feel that tubes sound more powerful.



The New PrimaLuna EVO Line-up: What’s different?

On paper they have very similar specs. Similar frequency bandwidth from the the EL34 tubes if you match their equivalent models in the series. However here are the key upgrades in the EVO Series.

  • New style front panel
  • Added headphone output
  • New power transformer higher voltage power output
  • Fuse holders mounted externally now, dont need engineer technicians to repair if they need fixing
  • Improved output transformers
  • Better quality capacitors from DuRoch
  • Laser engraving in the remote control
  • New tube covers


Including these changes, here are the ‘evolution’ / name changes of the previous PrimaLuna models

  • The EVO 100 replaces the ProLogue Classic
  • The EVO 200 replaces the ProLogue Premium
  • The EVO 300 replaces the DiaLogue Premium
  • The EVO 400 replaces the DiaLogue Premium HP


The New Tube DAC

The PrimaLuna EVO 100 Tube DAC is the first of it’s kind. It’s the world’s first tube-based data clocking device. They call it the SuperTubeClock! It replaces the solid state oscillator normally found in a DAC with a mini triode vacuum tube. By using a tube, they have significantly lowered the amount of jitter and noise, resulting in superior detail retrieval. This in turn yields superior detail and dynamics from top to bottom, and improved overall musicality.

It features a 24bit/192kHz upsampling Burr Brown SRC4192 chip set, and a premium DAC Burr Brown PCM1792A for the conversion. We highly recommend you give it a listen! It will be a long-term fixture in the showroom.

Rapallo | PrimaLuna EVO 100 DAC


We have 3 Brand New PrimaLuna EVO items in the showroom for you to feast your eyes on!

Visit our Auckland Showroom and ask for a demo of the:

  • PrimaLuna EVO 400 Power Amplifier
  • PrimaLuna EVO 400 Preamplifier
  • PrimeLuna EVO 100 Tube DAC

Rapallo | EVO 400 Combo photo



Sources: electroincsnote, Rapallo Ltd., PrimaLuna, Mullard Ltd. (1959), kenrockwell, ayonaudio

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