6L6GC-HARMA STR 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 6L6GC STR-CRYO has a number of features that make this ideal in all audio and guitar amplifier applications. The glass envelope is made from extra thick high grade glass which prevents microphonics. Internally the Harma 6L6GC-STR CRYO features gold grids and a high temperature alloy for the plates, giving the valve better heat transfer especially under overload situations.

Sonically the valve has a large dynamic range which contributes to
that big vibrant sound staging with long sustained notes The Harma 6L6GC-STR has a rich punchy tone with a nice open treble with a warm and detailed midrange, which is great for Fender style amplifiers.

The Cryo treatment transforms the sound of the standard item and provides more clarity and brilliance in the top end. The valve has a warmer and punchier midrange with great tonal dynamics.
This sound has made the Harma 6L6GC-STR CRYO our most sought-after 6L6GC.

As with all Harma valves, the 6L6GC-STR undergo our own unique real world burst testing. The burst testing process involves a series of varying timed electrical signal bursts. This runs the valves under the same stress conditions that they will meet in your amplifier. All out put valves are then dual matched by us on current and gain. This will ensure that you get the best selected valves available anywhere in the world.
They come dual matched on plate current and gain and are available
In matched pairs and quads. We do not supply this in single items.



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