The Ultimate Tone Vol. 6

Table of Contents and List of Figures/Tables


Chapter 1: DC POWER SCALING

DIRECT CONTROL
      Switching versus Linear
      Methodology
      Potentiometer Choice & Position
B+ REGULATORS
      First-principle Regulator
      Ratings for the Pass Element
      Stability
REDUCING POTENTIOMETER VOLTAGE
      Second Principle Regulator
CFPs
BIAS REGULATORS
      Tracking Basics
      Single-transistor Circuits
      Two-transistor Regulators
      Three-transistor Circuits
      Transistor Ratings
DISPARATE HIGH VOLTAGE RAILS
      “Light” Solution
REFINEMENTS & OPTIONS
      Swamped PS Pot
      PS Pot Taper
      Multiple PS Pots
      Tube Rectifier Simulation
      Remote Control
      Automatic Limiting
LONDON POWER’S KITS
DC-PSK-1
DC-PSK-2
SB-1
SB-2
VOLTAGE RANGE PROGRAMMING
      Super-Budget Options
CONTROL ANOMALIES
      VCK to the Rescue
      Oscillation
      SB Improvement
      “Where did the noise go?”
CATHODE-BIAS CONCERNS
      Curvy Curves
      Grid Control
      Cathode Control
      Variable Bias Resistor
MORE CIRCUITS
      All-N Regulators...
         ...With Diff-Amp
         ...as Conduction-Controlled
      Using Voltage Regulator Chips
      Mosfets and Op-Amps
      Cascode Output with Discrete Op-Amp
      Cascoding P-Channel Mosfets
      “Your basic pot”
      Bilateral Noise Suppression SUPER-FLEXIBLE FUTURE
      SF Evolution

Chapter 2: CLASS-G VALVE AMPLIFIERS

CROSS POLLINATION
      Modern Review
      Multi-tier Supply Rails
      Look-ahead Voltage Switch
      Applying the LVS to Tube Amplifiers
      Feedback From the Other Side
      Why Stop at Two?
      Tetrodes and Pentodes

Chapter 3: Z-B-X

TUBE AMPS 101
SE
      Push-Pull
      Unity-Coupling
UNLIMITED LIMITATIONS
      Tube Choice
PATENTLY PATENTABLE
      One Power Tube...
      One Zero-Cross Detector...
      ...And Pure Class-B
DRIVING THE TUBE
      “Class-B” Oddity
      Screen Drive
      BJT-Cascode
      Full-Wave Signal Rectification
      The “Switch” of the Zero-cross Switches
      Grid Signal Switching (as required)
VOLTAGE, CURRENT & POWER IN THE Z-B-X OUTPUT STAGE
      Z-B-X Voltage
      Current and Power
      The Legacy of Lethargy
OVERALL DESIGN
      Adding More Power Tubes...
      ...For Power
      ...As Presets
      ...As Channel Assignments
      ...For Asymmetry
ENHANCEMENTS
      Non-zero Idle Current
      Historical Precedent
      What About Cathode Bias?
      What about UL, triode and pentode modes?
SINGLE-TUBE FREE-FOR-ALL
      Half-Tube/Half-Mosfet
      Adding DC Balance
      Self-Split
      Virtual Drive

Chapter 4: DUMBLE

EVOLUTION
      Overdriven Amp Tone
DUMBLE’S OVERDRIVE
      Modified EQ
      Overdrive Circuit Proper
      Creating the Mythology
ERGONOMIC ISSUES
      Optimizing the Overdrive
      Adding a Third Drive Control
SWITCHABLES OTHER DETAILS
      Is the Hype Justified?

Chapter 5: THE 400

IN THE BEGINNING...
      BJTs Appear
      A Word About the Equations
100W STARTING POINT
      6550
      KT-88
      Expanding Each Design
EXTRACTING MAXIMUM POWER
      6550-max
      KT-88-max
      Looking at the “Max” Results
      Power Supplies
OTHER COMMON TUBES
      6L6GC
      Is it a Real 6L6?
      Sovtek 5881 & 6L6GB
      6CA7 / EL-34 / KT-77
      EL-509
      JJ EL-509
      EL-509 Overview
OTHER TUBES
CHASSIS SIZE

Chapter 6: MAINS CONTROL

PRIMARY MATTERS
      Primary Economy
      Core Discovery
      Primary Safety
PRIMARY WIRING
      Tapped Primary
      Dual Primaries
RANGE SELECTION
INDIRECT POWER & RANGE SWITCHING
      Relay Interface
      Solid-State Interface
      DPST Solid-State Switch
      Indirect Range Control
AUTOMATIC RANGE
      Linear Range Set
      Comparator Replaced by Detector
      Saving Relay Coil Power... Again
REPLACING RELAYS WITH MOSFETS
      Bilateral Switches
      Controlling the PVIs
      Adding Status LEDs
      Single-BJT Current-Steering
      Standby-PT Issues
      Range-PVIs Used as Power Switch
MULTI-RANGE CONTROL
      Voltage Clamps
      Voltage Adjustment Taps
      Expanded Voltage Level Detection
      High-Tap Priority
      Status Latch
      Control matrix
      Annunciating the Voltage Selection
      Under-Voltage Detection
      Over-Voltage Detection
      Tap Stability
INRUSH LIMITING
      Current-Limiter
      One Limit or Two?
      Limiter Voltage Drop
FURTHER ENHANCEMENTS
      Fuse Selection
MAINS DC
      Causes of Mains DC
      Blocking DC on AC Line
      Protecting the Caps
      Cap Options
      Everything Parallel

Chapter 7: SUSTAIN

TO CONTINUE...
      Attack
DYNAMIC-CURRENT DETECTION
      Sag and Sustain Signals
      Capacitive Coupling to Cathode
      Diode Signal Mixing
      Tube Rectifiers
      Precision Rectifiers
      Mixing the Signals...
      Plate Signal Sampling
      Plate Signal Rectification Error
CONDUCTION MODULATION
      Grid Modulation...
      Coupling the Sustain Signal into the Grids via Capacitors
      Conduction Variation via the Cathode
      Cathode Modulation Using Cathode-Derived Control Signals
EXTENDED USE

Chapter 8: HIGH GAIN

EVOLUTION
      In the Beginning...
      Whole-Amp Overdrive
      Bassman to Plexi
      Frequency Shaping Between Stages
CATHODE FOLLOWERS
      Origin
TUBE NOISE
CASCADES
MARSHALL
      The 800
      Interaction With the Next Grid
      Park
      2205
      SLX
      2466
      JVM
      Mode-Four
HIWATT
LANEY
      AOR-Series
      Klipp
      GH-100
      GH-100Ti
METALTRONIX
SOLDANO
LONDON POWER
      Sustainor
      Y-variations
BOGNER
KITTY HAWK
MESA BOOGIE
      Mk-1
      Mk-2
      Rectifiers
PEAVEY
      Butcher
      Triple XXX
      JSX
      Rockmaster
      Valve King
CARVIN
      Legacy
TRACE ELLIOT
      Speed Twin
GROOVE TUBES
      Trio
      Blackmore Signature
EGNATER
      TOL
TRAINWRECK
      Komet
      Attenuation & Emphasis
GAIN AGAIN


List of Figures
Fig. 1-1: Simple switching regulator
Fig 1-2: Charge and discharge currents of a filter cap
Fig. 1-3: Simple DC regulator
Fig. 1-4: Minimum regulation requirement for cathode-bias amp
Fig. 1-5: Minimum regulation requirement for a fixed-bias amp
Fig. 1-6: Typical screen supply derived from the plate supply
Fig. 1-7: First-principle plate regulator
Fig. 1-8: Controlling multiple B+ nodes from a single pot
Fig. 1-9: BJTs to Darlingtons in the first-principle regulators
Fig. 1-10: Darlington-triple regulators
Fig. 1-11: Replacing the Darlington input BJT with a jfet
Fig. 1-12: Mosfet replaces BJTs in plate/screen regulators
Fig. 1-13: Modelling the plate current load path
Fig. 1-14: Regulator/load power sharing
Fig. 1-15: Safe operating curve for mosfet and BJT
Fig. 1-16: Heatsink and mounting options
Fig. 1-17: Impedance of 100µF capacitor compared to ZOUT of mosfet circuit
Fig. 1-18: Degenerating the output impedance of the first-principle regulator
Fig. 1-19: Second principle regulator with voltage gain
Fig. 1-20: Second-principle regulator redrawn to highlight voltage ratios
Fig. 1-21: BJT diff-amp added to mosfet follower for regulator with gain
Fig. 1-22: Cascoded diff-amp
Fig. 1-23: Jfet diff-amp cascoded with BJTs and current-sourced two different ways
Fig. 1-24: Mosfet diff-amp circuit
Fig. 1-25: Single mosfet controls pass element
Fig. 1-26: Amplified follower regulator
Fig. 1-27: Control voltage in series or parallel with output voltage
Fig. 1-28: Basic CFP
Fig. 1-29: CFP with local feedback loop
Fig. 1-30: Cascoded CFP
Fig. 1-31: Jfet added to NPN cascode of CFP
Fig. 1-32: PNP cascode replaced by p-channel mosfet
Fig. 1-33: NPNs replaced by n-channel mosfet
Fig. 1-34: N-cascode replaced by single mosfet
Fig. 1-35: Tracking bias regulator essence
Fig. 1-36: Single-BJT bias regulator
Fig. 1-37: Shunt regulator
Fig. 1-38: London Power’s standard bias regulator
Fig. 1-39: Buffered shunt regulator
Fig. 1-40: Tracking B- regulator shown in TUT2
Fig. 1-41: “Familiar” diff-amp connection
Fig. 1-42: Buffered “standard” circuit
Fig. 1-43: Typical bias-set network
Fig. 1-44: High input-impedance low-capacitance amplifier
Fig. 1-45: The author’s jfet current-mirror
Fig. 1-46: Conventional photo-couplers and photo-isolators
Fig. 1-47: Interfacing the detector with a load
Fig. 1-48: Physical difference between photo-coupler and photo-isolator
Fig. 1-49: Photo-voltaic isolator
Fig. 1-50: Photo-voltaic relays
Fig. 1-51: Optically-controlled pass element
Fig. 1-52: Basic optical regulator
Fig. 1-53: Two optical regulators with current-steering added
Fig. 1-54: Reference voltage divider swamps PS resistance
Fig. 1-55: Linear and log pot tapers: rotation vs. output voltage
Fig. 1-56: Multiple PS pots
Fig. 1-57: Signal envelope and the effect of supply sag and power limiting
Fig. 1-58: Current-change signal injected into feedback node
Fig. 1-59: Current-change signal modulates PS voltage reference
Fig. 1-60: Connecting a remote PS pedal
Fig. 1-61: Multiple remote PS pedals
Fig. 1-62: Dedicated cable between multiple pedal-PS pots and amp with interlock
Fig. 1-63: Simplified multi-PS remote and channel switching
Fig. 1-64: Adding upper and lower limits to the PS pedal
Fig. 1-65: Automatic level audio modulation elements
Fig. 1-66: Jfet level control
Fig. 1-67: DC-PSK-1
Fig. 1-68: DC-PSK-2
Fig. 1-69: SB-1
Fig. 1-70: SB-2
Fig. 1-71: Altering the rates of change of the various regulators
Fig. 1-72: Relays used to select PS pots in SB-style circuit
Fig. 1-73: Issues using photo-voltaic relays to select PS pot wipers
Fig. 1-74: Action of the gate-shunt resistor during switching
Fig. 1-75: Instant-headroom option for SB-PS circuits
Fig. 1-76: Supply voltage variation with loading
Fig. 1-77: Supply unloading balances PS wiper position
Fig .1-78: VCK used for “entire amp” voltage clamping
Fig. 1-79: VCK used for driver and preamp supply node clamping (A) and for everything except VA (B)
Fig. 1-80: Eliminating oscillation by frequency-shaping the feedback loop of the bias regulator
Fig. 1-81: Frequency-shaping the plate regulator response
Fig. 1-82: Generic plate curves
Fig. 1-83: Concept of adding grid control to the cathode-bias Power Scale circuit
Fig. 1-84: Negative grid shift for decreasing plate supply
Fig. 1-85: Depletion-mode mosfet as variable RK
Fig. 1-86: Voltage-controlled current source replaces RK
Fig. 1-87: Altering the rate of change of IK
Fig. 1-88: Mosfet current-source
Fig. 1-89: Active bias resistor using rmx circuit
Fig. 1-90: RmX circuit with electronic control added
Fig. 1-91: Simplest all-n regulator
Fig. 1-92: Common-gate stage added to allow small pot in all-N regulator
Fig. 1-93: Extending the output voltage range to ground for previous circuit
Fig. 1-94: CS + CD all-n stages
Fig. 1-95: All-N diff-amp plus follower
Fig. 1-96: All-n with jfet input stage
Fig. 1-97: All-n jfet input with zener-stacked second stage
Fig. 1-98: All-n with jfet diff-amp
Fig. 1-99: All-n with jfet diff-amp and current-mirror constant-current source
Fig. 1-100: Conduction-controlled single-n
Fig. 1-101: Improved single-n conduction-controlled stage
Fig. 1-102: Conduction-controlled n-stage with floating supply
Fig. 1-103: Adding a jfet to the floating n-circuit
Fig. 1-104: All-n floating conduction-control with jfet diff-amp
Fig. 1-105: Constant-current source added to all-n floating conduction-control with jfet diff-amp
Fig. 1-106: Integrated-circuit regulator nomenclature and limits
Fig. 1-107: Mosfet pre-regulator for IC regulator
Fig. 1-108: Two ways to reduce the voltage losses of the hybrid IC-mosfet regulator
Fig. 1-109: Ground-referenced voltage control using noncritical pot and IC regulators
Fig. 1-110: N-channel mosfets used with an op-amp controller
Fig. 1-111: P-channel controlled by op-amp
Fig. 1-112: Discrete op-amp with cascode output and cascode driver
Fig. 1-113: Discrete op-amp with cascode driver split into two stages
Fig. 1-114: Cascode p-channel regulator
Fig. 1-115: Fixing the “non-zero” issue of the cascode p-channel regulator
Fig. 1-116: Cascode current source and p-channel cascode output stage
Fig. 1-117: Using a pot to vary VS directly
Fig. 1-118: Plot of IS versus VS and the resulting circuit resistance
Fig. 1-119: Current-source load for n-channel regulator
Fig. 1-120: Simple push-pull regulator
Fig. 1-121: Variation of the “Hood” amp as a regulator
Fig. 1-122: Push-pull regulator derived from audio power amp
Fig. 2-1: Ideal solid-state output stage with symmetric supplies
Fig. 2-2: Ideal solid-state output stage with multiple symmetric supplies
Fig. 2-3: Look-Ahead voltage switch
Fig. 2-4: Ideal push-pull tube output stage
Fig. 2-6: Multi-tier ideal tube push-pull amp with LVS
Fig. 2-7: LVS supply issues in the multi-tier tube amp
Fig. 2-8: Floating supervisory circuit to switch LVS
Fig. 2-9: Op-amp supplied in various ways
Fig. 2-10: Monitoring the speaker output to control the voltage selector
Fig. 2-11: Ideal tube extreme amp with single rail
Fig. 2-12: Ideal tube extreme amp with two rails
Fig. 2-13: Ideal tube extreme amp with three rails
Fig. 2-14: UL connection is the same as triode for power feed
Fig. 2-15: Fixed screen voltage
Fig. 2-16: Varied screen voltage
Fig. 3-1: Single-ended output stages
Fig. 3-2: Push-pull output stages
Fig. 3-3: Unity-coupled output stage
Fig. 3-4: Tetrode/pentode unity-coupled output stage
Fig. 3-5: Tube swapping made simple through user-adjustable bias controls
Fig. 3-6: Tube mixing and tube quantity variations in the TUT3 50W projects with four power tube positions
Fig. 3-7: Multiple output tubes with permanent assignment to preamp channels
Fig. 3-8: Assignable output tubes with multiple preamp channels
Fig. 3-9: Single-channel amp with selectable output tubes
Fig. 3-10: Tube spacing requirements
Fig. 3-11: Output stage simulated as switches
Fig. 3-12: Splitter as a switch
Fig. 3-13: Input and output of power tube switched by splitter
Fig. 3-14: Splitter as full-wave rectifier driving switched output tube
Fig. 3-15: The power path
Fig. 3-16: Block diagram of the ZBX amp
Fig. 3-17: Window comparator with typical gated output
Fig. 3-18: Simplified zero-cross using independent switches for the output stage
Fig. 3-19: Generic plate curves for tetrode/pentode power tube
Fig. 3-20: Conventionally-driven push-pull output stage idling at zero current
Fig. 3-21: RCA TT-5 Fig.17 & 18
Fig. 3-22: Screen drive using tubes
Fig. 3-23: Screen drive using semiconductors
Fig. 3-24: Screen modelled as a linear resistance
Fig. 3-25: Basic BJT-tube cascode
Fig. 3-26: Local op-amp controls BJT-cascode
Fig. 3-27: Op-amp based full-wave rectifiers
Fig. 3-28: Some tube full-wave rectifier circuits for audio
Fig. 3-30: London Power’s wide-band rectifier
Fig. 3-31: ZBX output stage switching for a single tube
Fig. 3-32: Drive-line switch considerations for grid-drive and screen-drive
Fig. 3-33: Drive-line switch options for BJT-tube cascode and local op-amp variations
Fig. 3-34: Voltage and current in the ZBX output stage
Fig. 3-35: Flyback voltages in a conventional amplifier
Fig. 3-36: Supply utility and efficiency of the output stage
Fig. 3-37: Commutating OT primary connection
Fig. 3-38: ZBX using full tube front-end and drive-line switching
Fig. 3-39: ZBX amp using tube front-end and hybrid drive
Fig. 3-40: ZBX with full solid-state front-end
Fig. 3-41: Adding more power tubes to the ZBX
Fig. 3-42: Traditional asymmetry combinations available with the ZBX amp loaded with two dissimilar tubes
Fig. 3-43: Asymmetry with a single tube
Fig. 3-44: Sequential asymmetry
Fig. 3-45: Adding a GMX module to the ZBX amp
Fig. 3-46: Providing an idle current path
Fig. 3-47: Peter Blomley’s 30W single-rail “new class-B” amp
Fig. 3-48: A modern update of Blomley’s design using split rails and op-amps
Fig. 3-49: Triode, UL and tetrode/pentode switching
Fig. 3-50: Simple mosfet push-pull with a tube
Fig. 3-51: Asymmetric saturation
Fig. 3-52: Traditional concertina idle conditions and asymmetric requirement for hybrid amp
Fig. 3-53: Cascode mosfet connection for improved voltage withstand rating
Fig. 3-54: DC balancing options
Fig. 3-55: Self-split differential output stage
Fig. 3-56: Super-balanced diff-amp output stage
Fig. 3-57: “Virtual” drive hybrid amp with expected signal flow
Fig. 3-58: Virtual drive with gain blocks interchanged
Fig. 3-59: Cathode bias for the virtual-drive amp
Fig. 4-1: Using a Fender reverb loop for extra gain
Fig. 4-2: Dumble’s basic topology
Fig. 4-3: Second preamp stage
Fig. 4-4: General form for inverting gain stage
Fig. 4-5: Feedback-controlled gain with frequency shaping
Fig. 4-6: Effect of capacitively bypassing the input resistor on the second stage
Fig. 4-8: Standard EQ lift and improved form, along with standard mid-shift form
Fig. 4-9: Overdrive section
Fig. 4-10: Frequency effect from different cathode-bypass cap values
Fig. 4-11: Plate coupling caps as frequency filters
Fig. 4-12: Plate shunt caps
Fig. 4-13: Completely separated signal paths
Fig. 4-14: Input stage shared with optional buffer
Fig. 4-15: Shared tubes with switched controls
Fig. 4-16: Trimpot-to-panel control conversion plus interstage attenuator fix
Fig. 4-17: Changing the value of the OD-Gain control in its new position
Fig. 4-18: Differentiating between a trimpot and panel control on a schematic
Fig. 4-19: EQ circuit position options
Fig. 4-20: Three features; three foot-switches
Fig. 4-21: Presettable features and one foot-switch
Fig. 5-1: Low and high frequency containing the same energy
Fig. 5-2: 100W application using a single pair of 6550s
Fig. 5-3: Plate curves for 6550
Fig. 5-4: Extrapolation of VG1=0V curve for different values of VG2
Fig. 5-5: Sine wave characteristics
Fig. 5-6: KT-88 100W-UL application circuit
Fig. 5-7: Expanded 6550 design
Fig. 5-8: Expanded KT-88 design
Fig. 5-9: KT-88 plate curves for VG2=300V
Fig. 5-10: 400W amp using six 6550s
Fig. 5-11: 400W KT-88 amp using six tubes
Fig. 5-12: Power supply for 6×6550 400W amp
Fig. 5-13: Power supply for 6×KT-88 400W amp
Fig. 5-14: 400W amp and power supply using real 6L6GCs
Fig. 5-15: 400W using 5881s
Fig. 5-16: 400W amp and supply for 6CA7 / EL-34
Fig. 5-17: 400W amp and supply using KT-77s
Fig. 5-19: Amperex EL-509 power amp
Fig. 5-20: JJ EL-509 curves
Fig. 5-21: Rack-style chassis
Fig. 5-22: Head-style chassis layout
Fig. 6-1: Tapped primary for 120V and 240V ranges with single fuse protection
Fig. 6-2: Adding a second fuse to the tapped primary: A-series fuses B-tap-specific fuses
Fig. 6-3: Dual primaries
Fig. 6-4: Dual primaries with individual fuses
Fig. 6-5: Approximation of dual-primaries when one winding is not working
Fig. 6-6: Range switch wiring for 120V/240V ranges
Fig. 6-7: Correct fusing of transformer windings
Fig. 6-8: Power switch with relay interface to mains current path - basic concept
Fig. 6-9: Power switch with active element in mains current path - basic concept
Fig. 6-10: Mimicking the DPST mechanical mains switch with mosfets and a small DPDT panel switch
Fig. 6-11: Modified gate drive circuit
Fig. 6-12: Relay control of both power and range
Fig. 6-13: Conserving coil power for the range relay
Fig. 6-14: Switchmode supply affords universal mains compatibility
Fig. 6-15: Voltage comparator monitors mains voltage to set range relay
Fig. 6-16: BJT mains voltage detection
Fig. 6-17: Saving range relay coil power in the automated system
Fig. 6-18: Bilateral switches used for range selection
Fig. 6-19: Heat issues for bilateral switches
Fig. 6-20: BJT selection of the bilateral switch PVIs
Fig. 6-21: Current-steering the PVI LEDs
Fig. 6-22: Adding LED annunciation to the circuits of Figs. 6-20 and 6-21
Fig. 6-23: Details of the current-steer LED control
Fig. 6-24: Voltage detection, PVI control and annunciating LED control with a single BJT
Fig. 6-25: Zener shunt regulator for standby supply
Fig. 6-26: Constant-current sink and zener shunt regulator
Fig. 6-27: Higher power composite zener and CCS using F-paks
Fig. 6-28: Bilateral range elements used for power function
Fig. 6-29: Simple control of range-PVIs for power function
Fig. 6-30: Keeping range and AC LEDs on in standby
Fig. 6-31: Front-panel “Power” LED supported by heater winding
Fig. 6-32: Voltage clamp used to compensate for primary voltage compromise
Fig. 6-33: Voltage regulators used to accommodate primary compromises
Fig. 6-34: Line adjusting transformer for single primary
Fig. 6-35: Single range vs. universal primary capabilities
Fig. 6-36: Dual-primaries with voltage adjustment taps and automation potential
Fig. 6-37: Zero-cross detector
Fig. 6-38: Voltage comparator stack
Fig. 6-39: Comparator and op-amp outputs
Fig. 6-40: High-priority gating
Fig. 6-41: Status latch
Fig. 6-42: Power control matrix with relays
Fig. 6-43: Power control matrix with bilateral switches
Fig. 6-45: Current-steer control of relay coils
Fig. 6-46: Display of detected voltage and matching
Fig. 6-47: Tap indicator and multiplication factor LEDs
Fig. 6-48: Status LEDs stacked on top of PVI LEDs in power control system
Fig. 6-49: Low mains indication and power shut down
Fig. 6-50: Seventh comparator added for over-voltage detection
Fig. 6-51: Over-voltage tie-in to priority gate and latch with annunciation
Fig. 6-52: Annunciation of specific voltage, including ‘low’ and ‘over’ ranges
Fig. 6-53: Protect LED with or without over/under LEDs
Fig. 6-54: Generating dither signals
Fig. 6-55: Integrating the signals into a varying voltage
Fig. 6-56: Flip-flop provides dither control
Fig. 6-57: Mosfet current limit for AC mains
Fig. 6-58: Single limit versus individual limits per primary
Fig. 6-59: Voltage losses in the current-limit circuit
Fig. 6-60: Floating supply for current limit
Fig. 6-61: PVI-powered current limiter
Fig. 6-62: Dual-limit PVI-powered current limiter
Fig. 6-63: DC offset voltage from external asymmetric loading of mains and resulting current in our PT
Fig. 6-64: Primary idle current with no load: with and without DC mains offset
Fig. 6-65: Asymmetric loading of PT by half-wave rectification
Fig. 6-66: Concept of DC blocker
Fig. 6-67: Functional DC mains blocker for any size guitar amp: version-1
Fig. 6-68: TO-220 and TO-3P diode packages
Fig. 6-69: Wiring a bridge two ways for different voltage clamp levels and current-handling abilities
Fig. 6-70: Series ESR
Fig. 6-71: DC mains blocker for any size guitar amp: version-2
Fig. 7-1: Note envelope and how sag works to produce the effect of increased sustain
Fig. 7-2: Sampling cathode current
Fig. 7-3: Adding the signals together using diodes
Fig. 7-4: Conduction error of real diodes
Fig. 7-5: Tube rectifiers
Fig. 7-6: Different current-sense resistor values generate different signal amplitudes
Fig. 7-7: Precision rectifier
Fig. 7-8: Virtual-earth mixer
Fig. 7-9: Discrete circuit for signal mixing
Fig. 7-10: Tube mixer
Fig. 7-11: Plate signal with resistive load
Fig. 7-12: Loudspeaker output with reference signal power and with “error” signal power
Fig. 7-13: “Difficult” tube rectification solutions for plate signals
Fig. 7-14: “Easy” tube rectification solutions
Fig. 7-15: Grid modulation for sustain control in cathode-biased output stage
Fig. 7-16: Three circuit positions for the Sustain control
Fig. 7-17: Tracking regulator provides sustain signal insert point
Fig. 7-18: Traynor Guitar Mate tremolo signal added to grid bias voltage
Fig. 7-19: Adding multiple bias pots to the trem-mix point above
Fig. 7-20: Capacitive coupling of sustain signal to output stage
Fig. 7-21: Right and wrong way to simplify capacitive mixing of sustain and audio signals
Fig. 7-22: Grid-leaks replaced by dual pot
Fig. 7-23: Cathode voltage modulation
Fig. 7-24: Cathode modulation using feedback-controlled elements
Fig. 7-25: Open-loop cathode modulation circuit
Fig. 7-26: Depletion-mode cathode modulator
Fig. 7-27: Log and square-law converters allow large signal inputs to control BJT and mosfet gates, respectively
Fig. 7-28: Jfet interface to reduce control sensitivity of circuit from Fig. 7-25 and 7-26
Fig. 7-29: Cathode-derived signals controlling a cathode-modulation element
Fig. 8-1: Grid-leak bias and cathode bias
Fig. 8-2: Fender gain stage and preamp architecture
Fig. 8-3: Typical Fender gain structure for entire amp
Fig. 8-4: Plexi gain structure including power amp
Fig. 8-5: Plate output frequency response for typical gain stage
Fig. 8-6: Frequency output of ‘bright’ input stage
Fig. 8-7: RKCK analysis of dual-input stage
Fig. 8-8: Common interstage attenuator used in early Fender and all Marshall amps
Fig. 8-9: De-emphasis of high frequencies
Fig. 8-10: Part of the Bassman 5E6-A preamp
Fig. 8-11: Improved EQ drive for Marshall icon
Fig. 8-12: Cathode follower isolates loading to boost gain
Fig. 8-13: Cathode follower output impedance shunts noise from driven elements to ground
Fig. 8-14: Cathode-follower input: A - Ground-referenced, B - Bootstrapped, C - Voltage-referenced
Fig. 8-15: A - Bootstrapped input stage, B - Voltage-referenced input stage
Fig. 8-16: 2204; not a good master volume
Fig. 8-17: 2204; the first significant MV amp
Fig. 8-18: Second stage of an 800
Fig. 8-19: Anatomy of an interstage attenuator
Fig. 8-20: Park amp using post-PI MV and cascaded input stages
Fig. 8-21: Marshall 2205 preamp
Fig. 8-22: Marshall SLX preamp
Fig. 8-23: Vintage-Modern 2466
Fig. 8-24: JVM (part 1)
Fig. 8-24: JVM (part 2)
Fig. 8-25: Hiwatt’s adaptation of the dual-volume preamp
Fig. 8-26: Cascaded inputs on Hiwatt
Fig. 8-27: Typical Laney cascaded preamp
Fig. 8-28: Laney Klipp
Fig. 8-29: Laney GH-100
Fig. 8-30: GH-100Ti
Fig. 8-31: GH-100Ti loop
Fig. 8-32: Metaltronix preamp
Fig. 8-33: Soldano SLO preamp
Fig. 8-34: Effects loop placement in Soldano amps
Fig. 8-35: London Power Standard Preamp
Fig. 8-36: Modified input stage for Sustainor preamp
Fig. 8-37: Later Sustainor lead channel
Fig. 8-38: Y-variant of LPSP
Fig. 8-39: Bogner Ecstasy lead channel
Fig. 8-40: Kitty Hawk four-channel preamp
Fig. 8-40: Kitty Hawk four-channel preamp
Fig. 8-41: Mesa Mark-1 preamp
Fig. 8-42: Mesa Mk-2
Fig. 8-43: Dual Rectifier preamp
Fig. 8-44: PV Butcher
Fig. 8-45: Peavey Triple-XXX preamp
Fig. 8-46: Peavey JSX amp
Fig. 8-47: Peavey’s noise gate
Fig. 8-48: Texture control
Fig. 8-49: London power double-ended ‘body’ control
Fig. 8-50: Legacy
Fig. 8-51: Speed Twin
Fig. 8-52: GT Trio
Fig. 8-53: ENGL Blackmore Signature
Fig. 8-54: Egnater TOL lead channel
Fig. 8-55: Komet
Fig. 8-56: Signal attenuation built into plate or cathode loads
Fig. 8-57: LDR replaces gain switch
Fig. 8-58: Tapped plate/cathode load provides frequency emphasis

List of Tables
TABLE 1-1: Alvaro’s Data
TABLE 5-1: KT-88 and 6550 ratings
TABLE 5-2: 6L6-family ratings
TABLE 5-3: 6CA7/EL34 and KT-77 ratings
TABLE 5-4: EL-509/6KG6 ratings
TABLE 5-5: EL-509 ratings