6L6GC-HARMA RETRO CRYO 6L6GC-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 6L6GC Retro Cryo is a re issue of the famous Sylvania STR 387 that was produced for Fender in the early 1970s. This was one of the most famous 6L6GC and sought after for it balanced and clear sound.

The valve is designed to break up later than many 6L6GC on the market in order to give that big Fender clean sound. The valve produces an even and rich soundstage without sounding muddy under full distortion. This is one of the best clean sounding current production 6L6GC made today. The treble is clear and smooth and has a nice chime when used in Fenders close to the old USA made Philips Sylvania sound. The design also has an extended treble response in order to spice up old vintage amps and also cater for the modern high gain sound.

The Cryo treated version offers a number of benefits particularly when the valve is pushed into distortion. It offers more clarity, cleaner more defined bass and a musical sparkle in the top end.

The Cryo 6L6GC retro offers new old stock sound quality with a modern price tag and is the ideal upgrade for all 6L6GC powered amplifiers. The Harma Retro Cryo valves also attained a 5 star review in Guitar Buyer magazine therefore making this the ideal upgrade

These we have dual matched which means they are matched on anode current and gain in matched pairs and quads.

All Harma Output valves are Dynamically Burst tested and undergo our own unique real world burst testing under real working conditions. The valve undergoes full drive testing which involves a series of varying timed electrical signal bursts that replicate the same stress conditions that the valve will encounter in your amplifier. Note No other supplier tests valves this way and why Harma valves have been used by the top Professionals. This is designed to ensure the ultimate reliability. The Harma valves have passed all the following tests:

Gain (m/A) Drive Tested)
Variable Signal Burst(Burst tested)
Transconductance (gm) Drive Tested
Output Drive Tested
Noise 1 (signal to noise)
Noise 2 (Aural)
Microphonics Test 1(Ambient)
Microphonic Test 2 (Shock)
Cathode Test
Grid Leakage Test

All output valves are then dual matched by us on anode current and gain. This will ensure that you get the best selected valves available anywhere in the world.



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