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What is a Phase inverter Amp Valve

The pre amp valve that drives the power tubes in a valve amp is often referred to as the Phase Inverter (PI) or the Phase Splitter.  Its primary role is to drive the power tubes.  A common set up is to use a double Triode pre amp tube like the ECC83 aka 12AX7 for this purpose.  The 12AX7 has 2 internal elements (triodes) which act individually from each other.  Valve Amp design is such that one half of this pre amp tube is designated to drive the left hand pair or single of the power tube section and the other half of the same preamp tube is designated the job of driving the right hand pair or single power tube (s).

A balanced selected preamp tube differs from a regular one in as much as the internal triodes have been deemed to have exactly the same drive, gain and characteristics as each other so internals are exactly matched.  This is generally not the case with most tubes and is not usually any cause for concern since each half within a preamp valve is often designated a different task within the amp to perform so does not need to be closely matched.  The benefit of using a balanced selected valve in the power tube driving or phase inverter position of a valve amp is that the power tubes are driven more evenly.

Where do I put the Balanced selected Phase inverter Amp Valve

Amp design is such that the signal path follows through starting from the input jack socket and finishing at your loud speaker so the first preamp valve in your amp (often labelled V1 and is sometimes fitted with a metal shielding cap) is NOT the phase inverter.  The Phase inverter sits right at the end of the signal chain just before and nearest the power tubes.  So if your amp has 3 preamp valves fitted the general rule is to fit the PI valve in V3 furthest from the input jack and nearest to the power tubes.  A common mistake is to fit the PI in V1 (the tube with the shielding fitted).  This is not correct.

Amp Valves Tubes How often do I Replace Them

How often Do I need to replace my Valves ?This is a question that is commonly asked about both preamp valves like the common 12AX7 ECC83 and also power valves like the EL34, 6l6GC, EL84.  The answer is not definitive but hopefully the following comments and things to listen out and look for may be [...]

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The Voc Rock 12AX7 B High Grade Valve

The NEW Voc Rock 12AX7 BWe finally achieved it.  Our very own 12AX7 Pre amp valve released and ready to go.  These valves are sourced from one of the worlds biggest and most reputable tube manufacturers as High Grade Low Noise valves.  We then run them through our meticulous burn in and test procedures to [...]

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Guitar Amp Valves VS HiFi Amp Valves

Guitar Amp Valves VS HiFi Amp ValvesExpelling the Myth about Guitar Amp valves being different to tubes used in HiFi and high end audio GearWe have a lot of our customers ask the question "I see you sell Guitar amp valves but do you have any tubes that I can use in my HiFi amplifier"?  [...]

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Tung-sol 12AX7 Review

Tung-sol 12AX7 Review The Tungsol 12AX7 is a high grade Russian valve. The valve is very well engineered and ruggedized using thick glass and firm internal supports. On test we very rarely see failures after burn in indicating good long term reliability. The gain factor of the valve is slightly [...]

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​How amp valves are made.

How amp valves are made.A great vid on the amount of effort that goes into making these wonderful tone machines.

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12AX7 Amplifier Valve Reviews

The humble 12AX7 ECC83 Valve is the most commonly produced and used Vacuum tube available today and still in current production by several large tube manufacturers. Largely renowned for its versatility, fantastic warm tone that valves are known for and an ability to produce pleasing overtones and distortion when overdriven in guitar amplification. This site has several audio reviews of [...]

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Valve Heater Glow

Valve Heater GlowEveryone that loves the look of Glowing shiny valves sitting on a high end Hi Fi amp or visible behind a Guitar Valve amp Head will have mixed reactions regarding the new Generation Preamp tubes being produced from the Russian Factories. To the Dismay of the "we love the valve glow" fans [...]

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How to Bias your Valve Amp

Biasing your Amp What is Biasing? The bias of a Valve amp is set by adjusting the grid voltages to set the idle current of the output tubes. This idle current can usually be set by adjusting a variable resistor (this can be visible in the form of a variable screw on the back of the amp [...]

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