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How KLD PVA 18 hand wired amplifier works

KLD PVA 18 hand wired amplifier based on Marshall TMB18 . T means Treble;M means Middle ; B means Bass.It is high gain 18 w tube guitar amp. Two impedance inputs , one is Low impedance input( active) , one is high impedance input( passive).
KLD PVA18 V1 V2
Preamp : V1B-V1A-V2B-V2A
The guitar signal is amplified by V1B (one 12AX7 triode) first which has a cold bias from its 1.5 k cathode resistor R1. Its 1uF(105) bypass cap C1 boosts the gain of mid and high frequencies which reduces the signal's lower frequencies early in the circuit so it can focus on mids and highs that sound good when later stages push into heavy distortion.
Magnetic guitar pickups are inductive, and require compensation, although this opportunity is also used for tone enhancement, not just correction. Without compensation, they have a strong low middle emphasis and little high frequency response - overall a very muddy and muffled sound.
The signal then flows through Preamp Volume potentiometer. The potentiometer's output flows to the V1A "cold clipper" gain stage.
The Attenuator Circuits: R17 and Gain control potentiometer
R17(1M) and Volume potentiometer (A1M)are made up of  attenuating , Which are an important part of high gain amp tone. This divider dumps 48% of the guitar signal to ground to keep from over  overdriving the following gain stages. Signal attenuating voltage dividers are present in all high gain tube amps to control the level of overdrive and saturation.
Cathode Follower: V2B
The Signal flows through same path the V2B preamp then directly through DC coupling (no coupling cap) to the V2A cathode follower which supplies the tone stack with a low impedance signal to keep the tone stack from loading down the guitar signal. After the Tone Stack the signal goes through the Master Volume and into the Phase Inverter. The Phase Inverter creates two mirror image signals that are 180 degrees out of phase to feed to the Power Tubes.
Tips: If you remove or bypass the R37 resistor in a voltage divider then there is no voltage divider. Removing C22 cap is a common mod for overly bright amps to cut ice pick highs and reduce shrillness.
Stack tone
In order to compensate guitar amp pickups low middle emphasis and little high frequency response - overall a very muddy and muffled sound, stack tone controls provided compensation for the natural sound of a pickup - the middle control simply boosts the pickup's normal 'middley' sound. The treble and bass controls do the
opposite , boosting higher and lower frequency levels, leaving a notch in-between for middle freq tone. So with typical settings of a bit of bass, middle and treble, the overall tone equalization complements the natural pickup sound for a balanced response of lows, mids and highs.
Comparing with stack tone control of Fender amp, Marshall amps are best at low-middle freq and crunchy rock tones, played at medium to high overdrive levels.
KLD PVA 18 tone stack

The Long Tail Pair Phase Inverter:Works
The Long Tail Pair (LTP) Phase Inverter (also called the cathode-coupled phase inverter) is the most popular phase inverter in guitar amplifiers due to its large output voltage swing and sweet overdrive tone. Unlike the non-amplifying cathodyne phase inverter used in many guitar amps the LTP phase inverter not only creates a dual mirror image signal stream but it also acts as a gain stage boosting the signal by about 1/4 of what two normal triode gain stages would. This added gain gives its output more voltage swing to drive big bottle power tubes to a fully distorted state. The LTP is a true differential amplifier and uses both halves of a dual triode tube (usually a 12AX7or 12AT7).
R21 is the tail resistor that creates the relatively high voltage needed for the cathode follower function of the V3A's cathode. It also supplies a near constant current flow shared between the two cathodes--as current increases through the V3A's cathode the current decreases through the lower and vice versa.
R11 is a standard bias resistor and creates a 1.5 volt difference between both tubes' grid and cathode. Its 1K5 ohm value shared between the two cathodes is the equivalent of each triode having a 3K ohm cathode resistor so the phase inverter is biased cold.
R10 and R12 are simply grid leak resistors which leak off DC grid current to maintain a steady DC bias voltage between the grid and cathode. The plate load resistors R14 and R15 are different values to balance the difference in gain between V3A and V3B.
R21 is the tail resistor that creates the relatively high voltage needed for the cathode follower function of the V3A's cathode. It also supplies a near constant current flow shared between the two cathodes--as current increases through the V3A's cathode the current decreases through the lower and vice versa.
The negative feedback signal from the output transformer's 4 ohm speaker tap is injected into the LTP phase inverter in one place: the lower grid through C8 and between the R21 tail resistor . The negative feedback signal on the lower grid counteracts the signal on the upper grid resulting in negative feedback attenuation. Injecting the NFB signal at R21 helps balance the feedback signal between the upper and lower triodes.
The Presence controls included high freq presence (SKY ) (SKY and C21) removes a variable amount of high frequency from the negative feedback signal, and low freq presence (EARTH)(Earth).
Reducing SKY negative feedback has the effect of boosting output so reducing the high frequencies in the negative feedback signal boosts high frequency output (C21 shunts the high frequency AC NFB signal voltage to ground).
Increasing C21's capacitance value will lower the cutoff frequency and bypass a larger range of frequencies to ground therefore boosting a larger frequency range at the speaker output.
Capacitor C10 suppresses oscillations above audio frequencies between the two triodes' plates to help stabilize the circuit.

KLD PVA 18 Phase Inverter
Power amplifier:EL84 push-pull class AB
Guitar signal from the Phase Inverter flows to the Power Tube grids. The signal is amplified and flows out the tube plates where one tube pushes the signal through the Output Transformer primary winding while the other power tube pulls. R13 and R16(2K2) are Gride stop resistor. Add grid stop resistors to help tame oscillation of amp,certainly it can reduce high freq tone in amp,but they need be within 10K.SW3 is switch of pentode and triode
The high impedance signal (high voltage but low current) flowing through the Output Transformer primary winding induces a low impedance signal (low voltage but high current) in the secondary winding which is connected to the Speaker Jacks. The guitar signal then flows through the speaker's voice coil and generates a magnetic field. The magnetic field interacts with the speaker magnet and causes the voice coil and speaker cone to move in and out generating air pressure waves our ears perceive as the sweet sound of electric guitar.
KLD PVA 18 Power tube
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