Heathkit ES-400 — Volume 8 — Cheatsheet (field-grade)

Condensed field reference for bench work, patching, and restoration — distilled from Vols 1–7

Panel 1 — Sub-Assembly Inventory and Tube Map

Complete Sub-Assembly Roster

Model	Qty	Function	Tubes per Unit	Notes
ES-2	1	Amplifier Power Supply	13 tubes: 1×5651, 3×12AX7, 3×6U8, 2×6080, 1×6BX7, 2×5R4GY, 1×5U4GB	~43 lb; regulated ±250 V @ 250 mA, −450 V @ 50 mA, 6.3 VAC @ 12 A + 6.3 VAC @ 2.5 A
ES-50	1	Reference Power Supply	2×6X4, 2×6U8, 1×5651	Regulated ±100 V DC reference rails used by all 15 amplifiers
ES-100	3	Initial Condition Power Supply	2×OB2 per unit	Each supplies 2× floating 100 V; 6 IC voltages total across the three units
ES-151	1	Relay Power Supply	None (passive network)	~50 V; drives the two operational relays on the front panel
ES-201	15	DC Operational Amplifier	3 tubes + 1 NE-51	Gain ≈ 50,000; output ±100 V @ 10 mA max
ES-400	1	Cabinet and Front Panel	—	364 banana jacks, 52 switches, 38 pots, 14 connectors, 1 DC milliammeter
ES-505	1	Repetitive Oscillator	1×6J6	0.6–6 Hz; drives automatic IC/Operate cycling for scope display
ES-401	1	Constant-Voltage Transformer	—	250 VA; conditions AC mains before ES-2; mounts in bottom cabinet bay
ES-600	1	Function Generator (optional)	—	Piecewise-linear approximation; 10 segments; connects via rear Varicon socket

Quick check: a complete Group C system has 25 sub-assemblies (counting 3× ES-100 and 15× ES-201 individually). Missing assemblies most commonly found absent: all or some ES-201 modules (tubes pulled and sold), ES-600 (optional), original patch cords.

ES-201 Tube Complement (per module × 15 modules)

┌─────────────────────────────────────────────────────────────────────┐
│                ES-201 TUBE MAP (one of 15 modules)                  │
│                                                                     │
│  INPUT                                                              │
│  JACKS      ┌────────┐    ┌────────┐    ┌────────┐    OUTPUT       │
│  ──[R_in]──►│ 12AX7  │───►│  6BQ7  │───►│  6BH6  │───►  JACK      │
│             │ Dual   │    │ Dual   │    │ Pentode│        │        │
│             │ Triode │    │ Triode │    │  IF    │        │        │
│             │ High µ │    │ TV     │    │  type  │        │        │
│             └────────┘    └────────┘    └────────┘        │        │
│                                                           │        │
│  FEEDBACK   ◄────────────────────────────────────────────┘        │
│  [C or R plug-in]                                                   │
│                                                                     │
│  OVERLOAD INDICATOR:  NE-51 neon lamp — lights at output saturation │
│  BALANCE POT:  front-panel trim per amplifier                       │
└─────────────────────────────────────────────────────────────────────┘

Tube	Type	Function	Replacement Notes
12AX7	Dual triode, 9-pin noval	High-gain input stage	Chinese new-production acceptable; ~$9.59 ea from Antique Electronic Supply
6BQ7	Dual triode, 9-pin noval	Intermediate gain / TV tuner type	NOS preferred; source from eBay/tube dealers
6BH6	Sharp-cutoff pentode, 7-pin	Output/buffer stage	Common IF amp tube; NOS from eBay
NE-51	Neon indicator lamp	Overload indicator per amplifier	Available new from general electronics suppliers

Total active vacuum tubes: 45 tubes across the 15 ES-201 modules (3 per module), visible through the top of the cabinet. Additional rectifier/regulator tubes reside inside the ES-2 power supply, bringing the system total to 73 tubes (per Operational Manual / Research Guide; source: ES-400 specification data).

Note — The 12AX7, 6BQ7, and 6BH6 socket types are different (9-pin noval for the first two; 7-pin for the 6BH6). Do not swap socket types during restoration. Verify pin-out against the ES-201 schematic before inserting any tube.

Panel 2 — Front Panel / Patchbay Quick-Reference

Front Panel Element Count

Element	Quantity	Purpose
Banana-plug jacks	364	All signal routing, power taps, reference taps
Potentiometers (coefficient)	30	Scaling constants 0–1 (10-turn vernier; see Panel 3)
Auxiliary 10-turn pots	2	Extended-range coefficient setting
Total pots	38	Includes balance, meter-select, and IC adjust pots
Toggle switches	52	IC/Operate/Hold per amplifier, relay controls, power
Multi-pin connectors	14	Internal harness + ES-600 Varicon rear connections
DC milliammeter	1	Front-panel readout for any selected amplifier output

Front-Panel Zone Map (top-view, left → right)

┌──────────────────────────────────────────────────────────────────────────────┐
│  ES-400 FRONT PANEL — ZONE OVERVIEW (operator faces this surface)            │
│                                                                              │
│  TOP ROW (tubes visible above):                                              │
│  [AMP 1]  [AMP 2]  [AMP 3] ... [AMP 15]   — 15× ES-201 modules             │
│                                                                              │
│  ┌──────────────────────────────────────────────────────────────────────┐   │
│  │ LEFT SECTION        │ CENTER SECTION          │ RIGHT SECTION        │   │
│  │                     │                         │                      │   │
│  │ HISTORY / AUXILIARY │ MAIN PATCH FIELD        │ COEFFICIENT SET      │   │
│  │ POTS (10-turn × 2)  │ (bulk of 364 jacks)     │ (30 coefficient pots)│   │
│  │                     │                         │                      │   │
│  │ INITIAL CONDITIONS  │ AMPLIFIER SWITCHES      │ METER SELECT GROUP   │   │
│  │ (IC jacks, 6 float) │ (IC / OPERATE per amp)  │ (AMPLIFIER OUTPUT    │   │
│  │                     │                         │  jack + meter)       │   │
│  │ RELAY CONTROLS      │ OPERATE RELAYS (A, B)   │                      │   │
│  │                     │                         │ REFERENCE SUPPLY     │   │
│  │ POWER SWITCHES      │ OSCILLOSCOPE OUTPUTS    │ (±100 V ref jacks)   │   │
│  │ (MAIN / HV / IC)    │ (HORIZ, VERT, GATING)   │                      │   │
│  └──────────────────────────────────────────────────────────────────────┘   │
│                                                                              │
│  METER: DC milliammeter — reads output of any selected ES-201               │
└──────────────────────────────────────────────────────────────────────────────┘

Key Jack / Switch Functions

Label / Control	Function	Operating Notes
AMPLIFIER OUTPUT	Measures selected amp via front meter	Set AMP SELECTOR switch first; remove all inputs before zeroing balance
±100 V REF jacks	ES-50 regulated reference taps	Low-impedance; do not short — connect through coefficient pot
IC jacks (6 floating)	Initial condition voltage sources	Floating — isolated from chassis and signal ground; set with IC pot before applying
OPERATE / IC / HOLD toggle per amp	Selects amplifier operating mode	IC: amp output held at IC voltage; OPERATE: integrates/sums; HOLD: freezes output
RELAY A / B	Operational relay switching	Energized by ES-151 supply; can switch patch connections under program control
OSCILLATOR	ES-505 output jack	Drives IC/Operate cycling for repetitive display; 0.6–6 Hz range
COEFF SET	Per-pot group: 30 single-turn + 2 ten-turn	Read pot dial; see Panel 3 for exact transfer function
HORIZ / VERT / GATING	Oscilloscope output jacks	Route any two amplifier outputs to scope; GATING drives Z-axis unblanking
METER (front)	DC milliammeter	Null indicator for balance; reads output voltage scaled by internal resistor

Note — The connection spacing between jacks is 3/4 in. General Radio double-banana plugs (or equivalent 2 mm banana plugs) are the correct connector type. The Operational Manual specifies polystyrene-type capacitors for integration feedback — do not substitute electrolytic types in integrator feedback positions.

Panel 3 — Scaling Formula Card

Amplifier Transfer Functions

╔══════════════════════════════════════════════════════════════════════╗
║  SUMMER (resistor feedback, resistor inputs)                        ║
║                                                                     ║
║         e_out = −[ (R_f/R_1)·e_1 + (R_f/R_2)·e_2 + ··· ]        ║
║                                                                     ║
║  Equal resistors → gain = −1 per input (inverter / sign-changer)  ║
║  Mix R values → weighted sum / difference (sign-inverted at output)║
╠══════════════════════════════════════════════════════════════════════╣
║  INTEGRATOR (capacitor feedback, resistor input)                    ║
║                                                                     ║
║         e_out = −(1/RC) · ∫ e_in dt   +  e_IC                     ║
║                                                                     ║
║  R = 1 MΩ, C = 1 µF  →  τ = 1 s  (unity time scale)              ║
║  R = 1 MΩ, C = 0.1 µF →  τ = 0.1 s  (10× time compression)       ║
║  R = 0.1 MΩ, C = 1 µF → τ = 0.1 s  (10× time compression)        ║
║  e_IC sets initial condition at t = 0                               ║
╠══════════════════════════════════════════════════════════════════════╣
║  COEFFICIENT (pot + amplifier)                                      ║
║                                                                     ║
║  Single-turn pot:  k = 0 to 1  (linear, direct reading)            ║
║  10-turn aux pot:  k = 0 to 1  (10× vernier resolution)            ║
║  Combined with gain-10 amp:  k_eff = 0 to 10                       ║
╚══════════════════════════════════════════════════════════════════════╝

Amplitude Scaling Rule

The ES-201 output saturates at ±100 V (hard rail). The NE-51 indicator fires at saturation.

Machine variable	Real variable	Scale factor s
e (volts)	x (real units)	s = e / x
e_max = 100 V	x_max (estimate)	s = 100 / x_max

Danger — Sustained output saturation against a low-impedance load exceeds the 10 mA output rating of the ES-201. Patch verification should always begin with the source (upstream) amplifier outputs disconnected until approximate levels are confirmed on the meter.

Time Scaling Rule

Condition	Relation	Effect
Real time = machine time	τ = RC = 1 s (R=1MΩ, C=1µF)	Display requires slow chart recorder or X-T scope
Time compression n:1	Use RC = 1/n s (e.g. C=0.1µF for 10:1)	Faster solution fits oscilloscope; repetitive mode via ES-505 works well
Time expansion 1:n	Use RC = n s (e.g. C=10µF for 10:1)	Slows fast real phenomena to observable machine rate

Amplitude + Time Scale Combined

For a second-order ODE ẍ + 2ζω_n ẋ + ω_n² x = f(t):

Machine equation (all variables scaled by amplitude factor s, time by β):

  d²X/dτ² + 2ζ(ω_n/β)·dX/dτ + (ω_n/β)²·X = F(τ)/s

  where τ = β·t (machine time),  X = s·x (machine voltage)
  β = time-scale factor (β > 1 → compression)
  s = amplitude scale (V per real unit)

Pot settings:
  damping pot    = 2ζ(ω_n/β) / 10   [normalised to pot range 0–1 if gain=10]
  spring pot     = (ω_n/β)² / 100   [similarly normalised]

See Vol 3 (Scaling and Problem Preparation) for full worked examples.

Standard Plug-In Component Values

Component	Value	Time constant (with 1 MΩ)	Use
Feedback resistor	1 MΩ	—	Unity-gain summer
Feedback resistor	100 kΩ	—	Gain-10 summer
Integrating capacitor	1 µF	1 s	Standard integration
Integrating capacitor	0.1 µF	0.1 s	10× time compression
Integrating capacitor	10 µF	10 s	10× time expansion
Input resistor	1 MΩ	—	Unity-weight input
Input resistor	100 kΩ	—	Gain-10 input

Panel 4 — Patch Quick-Reference

Signal-Flow Conventions

PATCH CORD COLOR CONVENTION (standard for ES-400 field use)
──────────────────────────────────────────────────────────
  BLACK  ─── Signal ground / reference common
  RED    ─── Positive voltage signal paths
  YELLOW ─── Inter-amplifier signal cables (general)
  GREEN  ─── Feedback paths
  WHITE  ─── Coefficient / pot output connections
  (Any colour may be used — consistency per patch is the rule)

Standard Circuit Patches

INVERTER / SIGN CHANGER
─────────────────────────────────────────────────────────
  e_in ──[1MΩ]──► AMP_n INPUT
                  AMP_n FEEDBACK ──[1MΩ]──┐
                                          │ (connect fb jack back to
                  AMP_n OUTPUT ───────────┘  input bus via 1MΩ)
  e_out = −e_in
  Required whenever a sign flip is needed in a feedback loop.

INTEGRATOR
─────────────────────────────────────────────────────────
  e_in ──[1MΩ]──► AMP_n INPUT
                  AMP_n FEEDBACK ──[1µF]──┐
                  IC SUPPLY ─────────────► IC jack on AMP_n
                  AMP_n MODE SW ──────────  IC → OPERATE to start
  e_out(t) = −(1/RC)∫e_in dt + e_IC(0)

COEFFICIENT MULTIPLIER (gain 0–1)
─────────────────────────────────────────────────────────
  Source ──► POT_k WIPER ──► AMP_n INPUT (via 1MΩ)
  e_out = −k · e_source   (k set by coefficient pot dial)

SECOND-ORDER OSCILLATOR (harmonic oscillator / sine source)
─────────────────────────────────────────────────────────
  [assume ω²X exists]
  AMP_1 IN ──[1MΩ]── from AMP_2 output via pot (ω² setting)
  AMP_1 FDBK ──[1µF]──  →  AMP_1 OUT = −Ẋ
  AMP_2 IN ──[1MΩ]── from AMP_1 output
  AMP_2 FDBK ──[1µF]──  →  AMP_2 OUT = +X (sine)
  AMP_1 OUT = −Ẋ (cosine, 90° offset)
  Frequency: f = ω/(2π);  pot set to ω² / 100

SPRING-MASS-DAMPER  (3 amplifiers)
─────────────────────────────────────────────────────────
  AMP_1 (summer):
    IN_1 ──[1MΩ]── F(t) forcing function
    IN_2 ──[pot_c]── −Ẋ (from AMP_2 out)      [damping]
    IN_3 ──[pot_k]── −X  (from AMP_3 out)      [spring]
    FDBK ──[1MΩ]──  → AMP_1 OUT = −Ẍ
  AMP_2 (integrator):
    IN  ──[1MΩ]── AMP_1 OUT (= −Ẍ)
    FDBK──[1µF]──  → AMP_2 OUT = +Ẋ
  AMP_3 (integrator):
    IN  ──[1MΩ]── AMP_2 OUT (= +Ẋ)  [invert if needed]
    FDBK──[1µF]──  → AMP_3 OUT = −X
  Feedback: AMP_3 OUT → pot_k → AMP_1 IN_3
            AMP_2 OUT → pot_c → AMP_1 IN_2

ES-400 front-panel with patch cords installed

(reference — courtesy Nuts & Volts / David Goodsell)

Patch Signal-Flow Diagram (General Form)

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 700 200" font-family="monospace" font-size="11">
  <!-- Reference supply -->
  <rect x="10" y="70" width="80" height="40" fill="#d4e8ff" stroke="#336"/>
  <text x="50" y="88" text-anchor="middle" font-size="10">±100V</text>
  <text x="50" y="101" text-anchor="middle" font-size="10">REF (ES-50)</text>

  <!-- Coefficient pot -->
  <rect x="120" y="70" width="70" height="40" fill="#ffe8c0" stroke="#963"/>
  <text x="155" y="88" text-anchor="middle" font-size="10">COEFF</text>
  <text x="155" y="101" text-anchor="middle" font-size="10">POT k</text>

  <!-- Summer amp -->
  <polygon points="220,60 280,90 220,120" fill="#c8ffc8" stroke="#363"/>
  <text x="240" y="88" font-size="10">SUM</text>
  <text x="240" y="101" font-size="10">AMP</text>

  <!-- Integrator amp -->
  <polygon points="320,60 380,90 320,120" fill="#ffd0d0" stroke="#633"/>
  <text x="338" y="88" font-size="10">INT</text>
  <text x="338" y="101" font-size="10">AMP</text>

  <!-- Second integrator -->
  <polygon points="420,60 480,90 420,120" fill="#ffd0d0" stroke="#633"/>
  <text x="438" y="88" font-size="10">INT</text>
  <text x="438" y="101" font-size="10">AMP</text>

  <!-- Output box -->
  <rect x="510" y="70" width="70" height="40" fill="#e8ffe8" stroke="#363"/>
  <text x="545" y="88" text-anchor="middle" font-size="10">SCOPE /</text>
  <text x="545" y="101" text-anchor="middle" font-size="10">METER</text>

  <!-- Connections -->
  <line x1="90" y1="90" x2="120" y2="90" stroke="#333" stroke-width="1.5"/>
  <line x1="190" y1="90" x2="220" y2="90" stroke="#333" stroke-width="1.5"/>
  <line x1="280" y1="90" x2="320" y2="90" stroke="#333" stroke-width="1.5"/>
  <line x1="380" y1="90" x2="420" y2="90" stroke="#333" stroke-width="1.5"/>
  <line x1="480" y1="90" x2="510" y2="90" stroke="#333" stroke-width="1.5"/>

  <!-- Feedback loop -->
  <path d="M 480,90 L 480,160 L 155,160 L 155,110" stroke="#c00" stroke-width="1.5" fill="none" stroke-dasharray="4,2"/>
  <text x="300" y="175" text-anchor="middle" font-size="10" fill="#c00">FEEDBACK PATH (sign loop closes via inverter if needed)</text>

  <!-- IC input -->
  <line x1="350" y1="60" x2="350" y2="40" stroke="#00a" stroke-width="1.5" stroke-dasharray="3,2"/>
  <text x="355" y="35" font-size="9" fill="#00a">IC supply</text>

  <!-- Labels -->
  <text x="50" y="55" text-anchor="middle" font-size="9">Reference</text>
  <text x="155" y="55" text-anchor="middle" font-size="9">Scale k</text>
  <text x="250" y="55" text-anchor="middle" font-size="9">−Σ</text>
  <text x="350" y="55" text-anchor="middle" font-size="9">−∫</text>
  <text x="450" y="55" text-anchor="middle" font-size="9">−∫</text>
</svg>

Panel 5 — Power-Up / Power-Down Checklist

Power-Up Sequence

Danger — The ES-2 supply develops −450 V and ±250 V rails. The ES-50 operates at ±100 V. All surfaces inside the cabinet are live during operation. The front panel hinges forward (it is very heavy) — install locking tip-up support rods before reaching inside.

PRE-POWER INSPECTION
[ ] All 15 ES-201 modules seated and locked in their slots
[ ] All tube sockets occupied — no open sockets on powered modules
[ ] Front panel closed and latched
[ ] No patch cords installed yet (reduces transient load)
[ ] Confirm all amplifier MODE switches are in IC position
[ ] Confirm MAIN POWER switch is OFF
[ ] Confirm COEFFICIENT SET pot group switches to "POT" position (not "EXT")

POWER-UP (normal sequence)
[ ] 1. Apply AC mains — MAIN POWER switch ON
[ ] 2. Allow 60 s minimum warm-up before applying high voltage
        (Operational Manual specifies: "Allow tubes to warm up for at least
         30 minutes before working with the computer" — abbreviated warmup
         acceptable for quick checks but full thermal settle takes 30 min)
[ ] 3. HIGH VOLTAGE switch ON — verifies ±250V and −450V rails
[ ] 4. Confirm ES-50 ±100 V reference: check ref jacks with DVM
[ ] 5. IC POWER switch ON — brings up ES-100 and ES-151 supplies
[ ] 6. Verify relay supply: ES-151 2× 50 V rails
[ ] 7. Balance all 15 ES-201 amplifiers (see Balance Procedure below)
[ ] 8. Install patch cords per problem setup
[ ] 9. Set initial condition voltages via IC pots
[ ] 10. Flip MODE switches from IC → OPERATE to run

BALANCE PROCEDURE (per ES-201, repeat for all 15)
[ ] a. Connect AMPLIFIER OUTPUT jack to front-panel meter via selector switch
[ ] b. Short all input jacks to ground (remove plug-in input resistors)
[ ] c. Adjust BALANCE pot for this amplifier until meter reads zero
[ ] d. Reinstall input and feedback plug-in components
[ ] e. Re-check: meter should return near zero with all inputs undriven

Power-Down Sequence

POWER-DOWN (normal sequence)
[ ] 1. Flip all MODE switches to IC (freezes integrator outputs safely)
[ ] 2. IC POWER switch OFF
[ ] 3. HIGH VOLTAGE switch OFF
[ ] 4. Allow 60 s for capacitors to partially discharge
[ ] 5. MAIN POWER switch OFF
[ ] 6. Allow 5 min before opening cabinet or touching internal components
         (ES-2 main filter caps can hold dangerous charge; verify with
          DVM across each electrolytic cap before touching any internal point)

Danger — Do NOT assume filter capacitors are discharged after power-off. Measure before touching. The −450 V rail is the most hazardous; it discharges through the bleeder resistor network but this takes time. See Panel 8 (Safety Card).

Panel 6 — Restoration Inspection and Recap Checklist

Pre-Restoration Assessment

PHYSICAL INVENTORY — check before ordering any parts
[ ] Count ES-201 modules present (target: 15; often fewer)
[ ] Count tubes per module (should be 12AX7 + 6BQ7 + 6BH6 + NE-51 each)
[ ] ES-600 Function Generator present? (optional; often missing)
[ ] All 364 banana jacks present and not stripped?
[ ] Original patch cords present?
[ ] Daca-Ware knobs all present and matching?
[ ] Front panel silk-screening legible?
[ ] Cabinet interior panels present (8 panels)?
[ ] ES-401 transformer and all supply transformers/chokes present?

ES-2 Amplifier Power Supply Recap

Component	Spec	Qty	Source
Main filter electrolytic (large axial)	20 µF @ 350 V through 70 µF @ 350 V (verify exact values on each cap)	16	Antique Electronic Supply (TubesAndMore.com)
Smaller electrolytic caps	Various, verify in-circuit	All present	AES / Mouser
Paper / wax caps	All values — replace regardless of reading	All present	AES, Mouser, Digi-Key
Carbon composition resistors (drifted)	Replace with 1% metal film equivalents	All	Mouser / Digi-Key

Note — Do NOT attempt to reform the ES-2 electrolytics. Age, storage conditions, and the extended power-off period make reforming unreliable on a one-of-a-kind machine. Replace all electrolytics unconditionally.

ES-201 Operational Amplifier Recap (per module × 15)

Component	Action	Notes
All resistors	Measure before removing; replace with 1% metal film	1% types were standard even originally; copper-oxide corrosion visible on metal end-caps indicates replacement needed
All capacitors	Replace unconditionally	Use polystyrene or silver mica for feedback positions; electrolytics for supply bypass only
3 tube sockets (9-pin noval × 2, 7-pin × 1)	Replace with new	Old phenolic sockets oxidize and cause intermittent contact
PCB traces	Inspect before and after desoldering	Two pad lifts per board are normal per the Goodsell restoration; repair with fine-gauge wire
NE-51 neon lamp	Replace if not lighting at overload	Standard NE-51; available new
Module housing (sheet metal)	Clean, prime, repaint	Satin black spray paint; verify no shorts to PCB after painting

Power Supply Checklist (ES-50, ES-100, ES-151)

[ ] ES-50 (reference supply):  replace all electrolytics and paper caps
[ ] ES-100 (×3 IC supplies):   replace all electrolytics and paper caps;
                                verify floating isolation — neither terminal
                                should have continuity to chassis ground
[ ] ES-151 (relay supply):     replace all electrolytics and paper caps

Cabinet Cosmetics

Item	Procedure	Cost Reference
8 interior steel panels	Sandblast to bare metal; powder-coat textured gray inside and out	~$180 for all 8 (Goodsell, 2019)
Star-lock washers	Install under all panel screws to cut through powder coat and maintain chassis ground continuity	Hardware store
Front panel masking tape residue	Remove by hand (fingernail preferred); then Meguiar’s Ultimate Compound; finish with 2 coats Meguiar’s Cleaner Wax	~$30 total
Missing or damaged knobs	Daca-Ware knobs; source from vintage Heathkit MM-1 VOM on eBay	$3–$20 per knob
Missing silk-screened labels	Custom dry-transfer (rub-down) sheet from CustomRubOnTransfers.com	~$65/sheet
Transformer / choke cans (rusty)	Disassemble; clean; prime; satin black spray paint	~$10–$20 paint

Restoration in progress — front panel removed

(reference — courtesy Nuts & Volts / David Goodsell)

ES-201 Tube Sourcing Quick-Reference

Tube	Preferred Type	Source	Approx. Cost (2019 ref.)
12AX7 × 15	Chinese new-production	Antique Electronic Supply	~$9.59 ea
6BQ7 × 15	NOS vintage	eBay, tube dealers	Varies
6BH6 × 15	NOS vintage	eBay (common IF type)	Varies
NE-51 × 15+	New production	Any electronics supplier	Cents ea

Panel 7 — Troubleshooting Quick-Triage

Symptom → Probable Cause → First Check

Symptom	Probable Cause(s)	First Check
No power, no pilot light	MAIN POWER switch, blown fuse, ES-401 transformer	Check fuse on ES-2; verify AC input at ES-401 primary
HV rails absent (no ±250 V)	ES-2 rectifier tubes, open filter cap, blown fuse	Measure B+ at ES-2 output terminals with DVM
±100 V reference wrong	ES-50 regulation failure, bad zener or tube	Measure ES-50 output directly; check reference jack on panel
All 15 amps unbalanced (meter won’t null)	ES-50 reference rail wrong, ES-2 supply out of spec	Balance requires stable ±100 V from ES-50 first
Single amp won’t balance	Bad 12AX7 (input stage), dirty pot wiper	Swap 12AX7 first (most likely); clean balance pot
NE-51 always lit on one module	Amp oscillating, missing or wrong feedback component, bad 6BH6	Check feedback jack — open feedback → oscillation → saturation
Integrator runs away	Positive feedback instead of negative; sign error in patch	Trace signal path; add inverter (sign-changer) in loop
Solution drifts at HOLD	Leaky integrating capacitor, 12AX7 grid current	Replace integrating cap (polystyrene is best); check 12AX7
IC won’t set correctly	ES-100 supply floating isolation lost	Check that neither IC terminal shows continuity to chassis
ES-505 oscillator not cycling	Bad tube or cap in oscillator	Check ES-505 output with scope at OSCILLATOR jack
Meter reads off-scale	Amplifier output saturated (NE-51 should also light)	Check patch: likely a sign error or missing initial condition
Repetitive display unstable on scope	ES-505 frequency not matched to scope sweep	Adjust ES-505 pot; or use scope’s external trigger from GATING jack
Function generator (ES-600) wrong shape	Segment slope pots mis-set, bad diode	Recalibrate slope/break voltage pots; check diodes (4× dual bias diodes on main panel also)
Front panel jack intermittent	Corroded banana jack contact	Clean with DeOxit; replace stripped jacks (banana jacks from eBay)

ES-201 Single-Module Fault Isolation Procedure

STEP 1 — Isolate module
  Remove all patch cords connected to the suspect amp.
  Set its MODE switch to IC.

STEP 2 — Check tube seating
  Remove and reseat all three tubes. Clean socket pins with DeOxit.

STEP 3 — Static balance check
  Short input summing junction to ground.
  Set MODE to OPERATE.
  Measure output at AMPLIFIER OUTPUT jack.
  Should read within ±2 V of zero after balance pot adjustment.
  → If cannot null: suspect 12AX7 input stage or balance pot.

STEP 4 — Open-loop gain check
  Apply a known small signal (~1 V) via 1 MΩ input resistor.
  With NO feedback component, output should immediately saturate ±100 V.
  → If not: check 6BQ7 and 6BH6 stages.

STEP 5 — Closed-loop summer check
  Install 1 MΩ input + 1 MΩ feedback.
  Apply 50 V reference. Output should be −50 V ±1 V.
  → If wrong gain: resistor values suspect; check plug-in components.

STEP 6 — Integrator check
  Install 1 MΩ input + 1 µF feedback. Set IC to 0 V.
  Apply +10 V input. Output should ramp at −10 V/s.
  → If ramps wrong direction: sign error in patch.
  → If ramps too fast/slow: capacitor value wrong.
  → If drifts with zero input: leaky cap or grid current.

Power Supply Voltage Quick-Check Table

Test Point	Expected Value	Tolerance	Note
ES-2 +250 V rail	+250 V DC	±5%	Regulated; check at supply terminal strip
ES-2 −250 V rail	−250 V DC	±5%	Regulated
ES-2 −450 V rail	−450 V DC	±5%	Regulated; highest voltage in system
ES-2 heater AC (winding 1)	6.3 VAC	±5%	@ 12 A max; measure at ES-201 socket pins
ES-2 heater AC (winding 2)	6.3 VAC	±5%	@ 2.5 A max; auxiliary filament winding
ES-50 +100 V	+100 V DC	±1%	Reference; tight regulation required
ES-50 −100 V	−100 V DC	±1%	Reference
ES-100 (each IC supply)	0–100 V floating	Set by IC pot	Floating — isolated from ground
ES-151 relay supply	2× 50 V DC	±10%	Less critical; relay pull-in only

Panel 8 — Safety Card (High Voltage)

Danger — The ES-400 operates at voltages that are immediately lethal. The ES-2 supply develops −450 V and ±250 V DC. The ES-50 develops ±100 V. The ES-100 IC supplies each develop up to 100 V floating. None of these voltages are safe to contact. A 50 mA shock across the chest is fatal; the ES-2 is rated 250 mA @ ±250 V.

Hazard Map

╔═══════════════════════════════════════════════════════════════════════╗
║  ES-400 HIGH-VOLTAGE HAZARD MAP                                      ║
║                                                                      ║
║  ZONE A — ES-2 Power Supply (~43 lb chassis, rear-lower cabinet)    ║
║  ┌─────────────────────────────────────────────────────────────┐    ║
║  │  −450 V @ 50 mA   ← HIGHEST RAIL — MOST DANGEROUS          │    ║
║  │  +250 V @ 250 mA  ← PLATE SUPPLY (lethal current)          │    ║
║  │  −250 V @ 250 mA  ← PLATE SUPPLY (lethal current)          │    ║
║  │  Bleeder resistors present; still dangerous minutes post-off │    ║
║  └─────────────────────────────────────────────────────────────┘    ║
║                                                                      ║
║  ZONE B — ES-50 Reference Supply (upper rear)                       ║
║  ┌─────────────────────────────────────────────────────────────┐    ║
║  │  +100 V / −100 V DC  ← hazardous; cardiac threshold ~50mA  │    ║
║  └─────────────────────────────────────────────────────────────┘    ║
║                                                                      ║
║  ZONE C — ES-100 IC Supplies (×3, upper row)                        ║
║  ┌─────────────────────────────────────────────────────────────┐    ║
║  │  Up to 100 V FLOATING — isolated from chassis ground        │    ║
║  │  Both terminals can be above or below ground potential      │    ║
║  └─────────────────────────────────────────────────────────────┘    ║
║                                                                      ║
║  ZONE D — Front Panel Jacks (operator-accessible)                   ║
║  ┌─────────────────────────────────────────────────────────────┐    ║
║  │  ±100 V present at REF jacks and AMPLIFIER OUTPUT jacks     │    ║
║  │  during operation — do not probe with bare fingers          │    ║
║  └─────────────────────────────────────────────────────────────┘    ║
║                                                                      ║
║  ZONE E — ES-201 Tube Tops (visible, accessible from above)         ║
║  ┌─────────────────────────────────────────────────────────────┐    ║
║  │  Tube pins near sockets: −450 V / +250 V present on pins   │    ║
║  │  during operation. Never probe pins with power on.          │    ║
║  └─────────────────────────────────────────────────────────────┘    ║
╚═══════════════════════════════════════════════════════════════════════╝

Safety Rules — Non-Negotiable

Danger — These rules are not suggestions. Violation of any of them can be lethal.

One hand in pocket rule. When probing internal points with power applied, keep the non-probe hand behind the back or in a pocket. This prevents a current path across the chest through both arms.
Measure before touching. After power-down, measure voltage across every large electrolytic capacitor in the ES-2 with a DVM before contacting any internal point. Bleeder resistors discharge slowly; the −450 V rail may retain lethal charge for several minutes.
Never open the cabinet alone. High-voltage work requires a second person present and aware of the hazard.
Do not defeat interlocks or safety hardware. The ES-400 chassis ground is electrically isolated from signal ground by design (see Vol 2). Do not connect chassis to signal ground to “fix” a ground loop — this is intentional design.
Insulated probes only. Use 1000 V CAT-II rated probes minimum for all internal measurements. Standard 600 V probes are insufficient for the −450 V rail if probe insulation is degraded.
Variac bring-up for post-restoration first power. After any significant restoration work, bring up AC mains voltage gradually via a Variac (0 → 120 V over 10–15 minutes) while monitoring supply output rails with a DVM. This limits inrush current and allows early detection of leaky capacitors before they fail catastrophically.
HV capacitors in the ES-2. The 16 large axial electrolytics can store significant energy. Even after bleeder discharge, treat them as charged until measured. Short them with a 10 kΩ, 5 W resistor across the terminals (not a direct short — the resistor limits discharge current).
Tube removal with power off only. Never insert or remove ES-201 modules or individual tubes with power applied.

Emergency First Aid (electrical shock)

Danger — In the event of electric shock, do NOT touch the victim until the power source is confirmed off. Switch off the MAIN POWER switch, or pull the AC plug. Then call emergency services immediately. Even if the victim appears conscious, cardiac arrest can be delayed by minutes following high-voltage shock.

System Block Diagram

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  <text x="50" y="52" text-anchor="middle">110 VAC</text>
  <text x="50" y="63" text-anchor="middle">60 Hz</text>

  <!-- ES-401 -->
  <rect x="120" y="35" width="80" height="35" fill="#ffe4b5" stroke="#c90" stroke-width="1.5"/>
  <text x="160" y="52" text-anchor="middle">ES-401 CVT</text>
  <text x="160" y="63" text-anchor="middle">250 VA</text>

  <!-- ES-2 -->
  <rect x="230" y="25" width="100" height="55" fill="#ffd0d0" stroke="#c00" stroke-width="2"/>
  <text x="280" y="42" text-anchor="middle" font-weight="bold">ES-2</text>
  <text x="280" y="54" text-anchor="middle">+250V/250mA</text>
  <text x="280" y="64" text-anchor="middle">−250V/250mA</text>
  <text x="280" y="74" text-anchor="middle">−450V/50mA</text>

  <!-- ES-50 -->
  <rect x="230" y="100" width="100" height="40" fill="#d0d0ff" stroke="#009" stroke-width="1.5"/>
  <text x="280" y="117" text-anchor="middle" font-weight="bold">ES-50</text>
  <text x="280" y="130" text-anchor="middle">±100V REF</text>

  <!-- ES-100 x3 -->
  <rect x="230" y="160" width="100" height="55" fill="#d0ffd0" stroke="#060" stroke-width="1.5"/>
  <text x="280" y="177" text-anchor="middle" font-weight="bold">ES-100 ×3</text>
  <text x="280" y="189" text-anchor="middle">IC Supplies</text>
  <text x="280" y="201" text-anchor="middle">6× floating</text>
  <text x="280" y="211" text-anchor="middle">0–100V ea</text>

  <!-- ES-151 -->
  <rect x="230" y="235" width="100" height="40" fill="#ffe0ff" stroke="#909" stroke-width="1.5"/>
  <text x="280" y="252" text-anchor="middle" font-weight="bold">ES-151</text>
  <text x="280" y="265" text-anchor="middle">Relay 2×50V</text>

  <!-- ES-505 -->
  <rect x="230" y="295" width="100" height="40" fill="#fffff0" stroke="#990" stroke-width="1.5"/>
  <text x="280" y="312" text-anchor="middle" font-weight="bold">ES-505</text>
  <text x="280" y="325" text-anchor="middle">Osc 0.6–6Hz</text>

  <!-- 15x ES-201 -->
  <rect x="380" y="80" width="140" height="130" fill="#fff0e0" stroke="#c60" stroke-width="2"/>
  <text x="450" y="100" text-anchor="middle" font-weight="bold">15× ES-201</text>
  <text x="450" y="114" text-anchor="middle">DC Op-Amp</text>
  <text x="450" y="126" text-anchor="middle">Gain ≈ 50,000</text>
  <text x="450" y="138" text-anchor="middle">Out: ±100V</text>
  <text x="450" y="150" text-anchor="middle">@ 10mA max</text>
  <text x="450" y="162" text-anchor="middle">Tubes: 12AX7</text>
  <text x="450" y="174" text-anchor="middle">6BQ7, 6BH6</text>
  <text x="450" y="186" text-anchor="middle">+ NE-51 lamp</text>
  <text x="450" y="198" text-anchor="middle">per module</text>

  <!-- Front panel -->
  <rect x="380" y="230" width="140" height="95" fill="#e0f0ff" stroke="#369" stroke-width="2"/>
  <text x="450" y="248" text-anchor="middle" font-weight="bold">ES-400 PANEL</text>
  <text x="450" y="260" text-anchor="middle">364 banana jacks</text>
  <text x="450" y="272" text-anchor="middle">52 switches</text>
  <text x="450" y="284" text-anchor="middle">38 pots</text>
  <text x="450" y="296" text-anchor="middle">1 milliammeter</text>
  <text x="450" y="308" text-anchor="middle">14 connectors</text>
  <text x="450" y="318" text-anchor="middle">Patch field</text>

  <!-- Scope -->
  <rect x="580" y="120" width="100" height="45" fill="#f0fff0" stroke="#393" stroke-width="1.5"/>
  <text x="630" y="139" text-anchor="middle">OSCILLOSCOPE</text>
  <text x="630" y="151" text-anchor="middle">XY / XT mode</text>

  <!-- ES-600 optional -->
  <rect x="580" y="280" width="100" height="40" fill="#f5f5f5" stroke="#999" stroke-width="1" stroke-dasharray="4,2"/>
  <text x="630" y="297" text-anchor="middle">ES-600</text>
  <text x="630" y="309" text-anchor="middle">Func. Gen. (opt)</text>

  <!-- Power connections (red dashed = HV) -->
  <line x1="90" y1="52" x2="120" y2="52" stroke="#c90" stroke-width="2"/>
  <line x1="200" y1="52" x2="230" y2="52" stroke="#c90" stroke-width="2"/>

  <!-- ES-2 feeds ES-201 -->
  <line x1="330" y1="45" x2="370" y2="145" stroke="#c00" stroke-width="1.5" stroke-dasharray="4,2"/>
  <text x="340" y="95" font-size="9" fill="#c00">±250V, −450V</text>
  <text x="340" y="105" font-size="9" fill="#c00">6.3VAC heat</text>

  <!-- ES-50 feeds front panel reference jacks -->
  <line x1="330" y1="120" x2="380" y2="277" stroke="#009" stroke-width="1.5" stroke-dasharray="4,2"/>
  <text x="333" y="185" font-size="9" fill="#009">±100V ref</text>

  <!-- ES-100 feeds front panel IC jacks -->
  <line x1="330" y1="188" x2="380" y2="290" stroke="#060" stroke-width="1.5" stroke-dasharray="4,2"/>

  <!-- ES-201 → Front panel -->
  <line x1="450" y1="210" x2="450" y2="230" stroke="#c60" stroke-width="2"/>

  <!-- Front panel → Scope -->
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  <text x="535" y="220" font-size="9">Signal out</text>

  <!-- ES-505 → Front panel -->
  <line x1="330" y1="315" x2="380" y2="315" stroke="#990" stroke-width="1.5"/>
  <text x="335" y="310" font-size="8">0.6–6Hz</text>

  <!-- ES-600 optional connection -->
  <line x1="520" y1="300" x2="580" y2="300" stroke="#999" stroke-width="1" stroke-dasharray="3,2"/>

  <!-- ES-401 → ES-50, ES-100, ES-151 -->
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  <line x1="160" y1="120" x2="230" y2="120" stroke="#c90" stroke-width="1" stroke-dasharray="2,2"/>
  <line x1="160" y1="188" x2="230" y2="188" stroke="#c90" stroke-width="1" stroke-dasharray="2,2"/>
  <line x1="160" y1="255" x2="230" y2="255" stroke="#c90" stroke-width="1" stroke-dasharray="2,2"/>
  <line x1="160" y1="315" x2="230" y2="315" stroke="#c90" stroke-width="1" stroke-dasharray="2,2"/>

  <!-- Legend -->
  <rect x="10" y="350" width="330" height="60" fill="#f9f9f9" stroke="#999"/>
  <text x="170" y="365" text-anchor="middle" font-weight="bold">LEGEND</text>
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  <text x="65" y="382">High-voltage power (ES-2)</text>
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  <text x="65" y="397">AC distribution (ES-401 → supplies)</text>
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  <text x="225" y="382">Signal path</text>
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  <text x="225" y="397">Optional / ES-600</text>
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Quick ES-400 vs. EC-1 Comparison

Parameter	ES-400 (H-1)	EC-1 (desktop)
Op-amp modules	15× ES-201	9× (same ES-201 circuit)
Banana jacks	364	Fewer
Weight	168 lb	~35 lb
Original price	$945 (Group C)	~$200
Power	~450 W	Lower
Tube count	73 total	~28
Cabinet	Floor-standing, 2-bay	Desktop
Coefficient pots	30 + 2 auxiliary 10-turn	Fewer
IC supplies	3× ES-100 (6 floating voltages)	1–2
ES-505 oscillator	Included	Optional
Programming method	Identical — same ES-201	Same

Note — The EC-1 Operational Manual (freely available) provides the most complete programming tutorial for the ES-201 op-amp method and is directly applicable to the ES-400. See Vol 1 for full citation.

Cross-Volume Reference Index

Topic	Volume
Full system overview, history, and provenance	Vol 1 — Overview & history
Hardware architecture, power supplies, ES-201 circuit	Vol 2 — Hardware & architecture
Computing elements, patchbay, integrator, summer, bias diodes	Vol 3 — Computing elements & patchbay
Acquisition, inspection, restoration, recap, bring-up	Vol 4 — Acquisition & restoration
Programming methodology: scaling, patching, reading results	Vol 5 — Programming
Sample programs and demonstrations (six worked examples)	Vol 6 — Sample programs
Modern extensions, ADC/DAC bridge, hybrid use	Vol 7 — Modern extensions
This cheatsheet (condensed field reference)	Vol 8 — Cheatsheet

Fully restored ES-400 on the bench