Two Icon Audio GU81 Mono block amplifier units
Recently, valve amplifiers have made a comeback. In the 1960’s they dominated the audio market. Today they are beloved by audio enthusiasts for their warm sound and classic looks. Here we look at the origin of valves and what amplifiers are available today. Everything from headphone amplifiers to CD players has been given the valve treatment. Icon Audio is one of the leading makers and here we look at some of their products.
A brief history of valve amplifiers
Before transistors, there was another technology for amplification, based on thermionics. This used the emission of electrons from a heated cathode. The cathode and other elements were mounted inside an evacuated glass bulb. Consequently, the triode valve was invented in 1906 by Le De forest. The most common topology used a single-ended triode for amplification and was originally used to boost telephone circuits.
About 100 years ago three developments spurred the creation of better amplifiers. The first was the development of radio. Early radio circuits needed four or five valves to amplify the weak signals. Next came sound recording for records, using microphones rather than acoustical methods. Finally, amplifiers were needed in cinemas, for the new talking pictures.
What valve amplifiers are available today?
Today many companies have jumped on the valve bandwagon with mixed results. Icon Audio and Leak, are just two of the companies that make modern valve equipment. Icon audio make a wide range of hi-end valve equipment, including pre/ power amps, headphone amps and phono stages. Another well know company is Leak. Leak was a famous amplifier manufacturer in the 1950s and 60’s. In 2020 the company was reborn and you can now purchase a range of retro-styled amps with the original pedigree.
How do valve amplifiers work?
Valves need a number of voltages to operate, including the use of high voltages on the anode. This can be over two hundred volts in some cases. The heaters also need 6.3 volts and sometimes 5v for the rectifier. As a result the power supply needs a large and heavy transformer, with multiple windings. Additionally valves need an output transformer for each channel. With valve amplifiers the output transformers will get larger as the power rating increases.
Valve types in amplifiers.
There are three types of valves used in audio amplifiers. Triodes with three elements, a cathode, grid and heater and Tetrodes / Pentodes that have extra grids to improve performance. The ECC81 / 12AT7 is a common type of triode valve. The Valve ID system leads to a UK or US ID. They are essentially the same valve. Tetrodes have four elements and pentodes have five. They are commonly used as output valves and often KT66s or KT88s are used. Modern tubes are still manufactured or there are NOS or New Old Stock devices.
Where are new valves made?
There are three modern factories where new valves are made, they are in China, Russia and the Slovak republic. Certain companies tend to use a certain brand. For example the Guitar amplifier company, Spartan Music use Slovak tubes made by JJ Electronic Tubes. They are good quality at a reasonable price. Perhaps the biggest modern valve manufacturer is Shuguang in China. They have been making valves since 1958 and are renowned for their audio valves. They supply many of the OEM makers and the valves for kit built amplifiers.
The Icon Audio valve amplifier range
Icon Audio Stereo 25
Icon audio make a good range of valve amplifiers starting with the 15w per channel Stereo 20PP up to the 60w per channel Stereo 60. They also make the GU81 monoblock amplifier. With these you can use separate units for each channel , for example left, right and a sub woofer. The design ensures total separation and no crosstalk. The GU81 outputs 250 watts of power or there is a 100w pure triode version. Notably, some unusual valves have been pressed into service with audio amplifier manufactures and the GU81 is one such. This is a high power radio transmitting valve and glows an amazing cherry red.
The GU 81, the ultimate output valve?
The best output tubes are pure triodes as with the GU81. However triodes are inefficient, therefore a lot of power is needed to get a reasonable output volume. Hence using high power transmitting tubes. The GU81 is an unusual and large tube with not much information available from manufactures. As a result Icon have spent a considerable amount of time developing amplifiers that use them. In use the anode is dissipating 350 watts and glows a cherry red. However this is only operating at half power. These units are probably the ultimate in valve amplification. Next we look at a more affordable starter amp.
The stereo 20PP from Icon Audio, a good starting point.
In contrast, as an example of an affordable valve amplifier, we look at the Stereo 20PP from Icon audio. PP stands for push pull as there are two output valves. Push pull outputs are more efficient than single ended outputs. The Stereo 20 is based on a classic Leak design from 1955. It used the new Mullard EL84, and ECC83 valves and was an instant success. Original versions of the amplifier now sell for over £1500.
The Stereo 20 is good for smaller rooms and or efficient speakers. Higher output sources can be used such as CD players or DAC’s. Icon Audio also make valve based phono pre-amps. The sound of the Stereo 20 is transparent and is great for acoustic or orchestral music.
For the best in headphone sound there is a Separate winding on the output transformer. This gives more intimacy than with a solid state amplifier. Finally the EL84 output valve is very efficient, meaning that a smaller power transformer and output transformers can be used. Consequently, this reduces the price of the unit.
Valve phono stages, Icon Audio’s PS2 MM
Icon audio also make a range of hi-end valve phono pre-amps. The PS2 MM is a one-box moving magnet pre amp that can be also be used with moving coil cartridges, by using a transformer. This pre-amp is a good companion to the Stereo 20. It is classed as an entry level unit and will give you that warm valve sound from vinyl. The PS2 MM is hand built and also has a mono switch for the best of mono LP playback.