5U4GB-HARMA RETRO CRYO 5U4GB-HARMA RETRO CRYO Click on image(s) above to view larger

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Harma Deep Cryogenic treated valves offers improvements to the sonic character of the valves and results in sound characteristics only normally found in very expensive NOS valves such as Mullards. The process involves taking the vacuum tubes and freezing them down to -312 Fahrenheit and soaking these for a minimum of 12 hours. Then the temperature is held at this low level for 24 hours. The vacuum tubes are then slowly brought up to normal levels over the next 12 hours.

Metals respond very well to deep cryogenic process. The reasons are as follows, during the cooling or solidification phase of the manufacturing process, molecules are trapped in a haphazard pattern. This is down to stress caused in the bending and welding of the anode plate material. This random placement causes obstacles for electrons and when encountered this interference can cause noise, slow down electron flow and sound deterioration affecting the quality of the sound of the vacuum tube. .

At very cold temperatures (below -312 Fahrenheit), the molecules will align in a more uniform, compact structure through the removal of kinetic energy. When the material is returned to ambient temperature, this new uniform, compact pattern is maintained, Thus changing the structure of the nickel permanently. This process makes a permanent change and the benefits do not deteriorate over time or upon return to operating temperature, it changes the whole way the vacuum tube performs.

The biggest benefits I have found have been a dramatic improvement in the sound quality. The bass response has been clearer with reduction in microphonics and clear more transparent highs. Cryogenic treatment has now become a way for a modern valve to produce a sound quality that approaches the iconic originals.
The Harma Retro Cryo 5U4GB is a specially Cryogenically treated version offering the ultimate in performance.

The Harma 5U4GB Retro Cryo is designed on the military grade Philips/Sylvania 5U4GB that was used extensively in audio and commercial electronics in the 1960's. The Harma 5U4GB is fully interchangeable with a 5U4G and has the dual advantage of standing approx. 90mm tall excluding the base with straight sides which allows fitting in small enclosures.
The design features high grade nickel formed in two large box anode plates which are pleated together with internal supports, just like the original USA design. The valve is also internally braced to prevent vibration in guitar amplifier applications. The Harma 5U4GB Retro have proved to be long lasting in demanding applications such as Mesa Boogie Single, Dual and Triple rectifier's amplifiers and work very well in all Fender amplifiers such as the reissue Bassman 1959.

All Harma rectifier valves undergo testing under real working condition and the voltage drop is measured between each plate and the cathode. This ensures correct conformity to design parameters under working conditions.



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