HERE IS WHAT GOES ON INSIDES THIS AMP
The guitar’s alternating current audio signal enters the amplifier at the 1/4” input jack.
The 1 megaohm resistor soldered to the input jack is the ‘input resistor.’ It sets the amp’s input impedance to 1,000,000 ohms (1M) to boost the signal voltage from the guitar.
This small signal then flows through a shielded wire soldered to the input jack and then on to the EF86 preamplifier tube’s control grid. To eliminate noise, a very high quality and low impedance shielded input wire is used.
The preamplifier tube amplifies the guitar audio signal and then sends it out pin 6 (the tubes plate) to the .01uF coupling capacitor that is located on the tone control turret board. Coupling caps are sometimes also called ‘blocking caps’ because they block DC voltage but allow the AC guitar signal to pass.
The 0.01uF written on the capacitor is it’s rating of 0.01 microfarads (0.000,000,001 Farads). After this .01uF capacitor, a wire is soldered between its termination and the input connection lug of the volume potentiometer so the volume created can be controlled by the end user.
High voltage DC (direct current) power used to power the EF86 preamplifier tube is brought in through a 220k plate resistor, which also can be called a load resistor.
This load resistor is connected to the EF86 tube’s plate. The load resistor changes the amplifier circuit from a current oriented amplifier to a voltage oriented amplifier. This resistor also allows a small flow of current from the tube’s plate to make a large change in voltage thus creating a voltage amplifier.
The load resistor restricts the flow from the power supply (connected to the first input side of this resistor) to the tube’s plate (connected to the output side of this resistor). When the tube flows negatively charged electrons to the positively charged plate the voltage drops across the load resistor and between the load resistor and plate.
If you slow the flow of electrons from the cathode to the plate, the voltage drop across the load resistor will decrease causing a voltage rise on the plate. Stop the flow completely and the voltage on both sides of the load resistor will equalize. If there’s no current flowing there will be no voltage drop across the load resistor.
The EF86 preamplifier tube’s control grid ‘releases pressure’ (lowers voltage) by flowing negatively charged electrons onto the positively charged plate. The electrons are pulled by the power supply toward the load resistor but they stack up when they hit the load resistor – this is what causes the voltage drop across the plate resistor – there are more electrons on one side of the resistor. More stacked up electrons = lower voltage on the plate. When the control grid slows the flow of electrons the voltage rises on the plate because the power supply is constantly pulling electrons through the plate resistor (fewer electrons = higher voltage). These voltage fluctuations on the plate are the amplified guitar audio signal.