Collins 516F-2 & S-Line
The Switched Neutral AC Power Design Defect

Section 1 — The Switched Neutral Defect

How the Collins S-Line Power System Works

The 516F-2 has no power switch of its own. It is controlled by the on/off switch in the associated transceiver or transmitter via specific pins of the 11-pin power cable. The front-panel switch interrupts the AC circuit, de-energising the 516F-2 transformer. The problem is which conductor is interrupted.

The single-pole power switch is connected in the neutral conductor of the mains circuit — confirmed in community discussion: “Even Collins did the switching of the neutral even up through the 516F-2.”¹ Interrupting the neutral stops current from flowing, so the equipment is functionally off. But the active conductor remains permanently connected to the transformer primary, fuse, and all primary-side components, including the Y-class mains filter capacitors, at full mains voltage — at all times the mains plug is inserted.

  SAFE DESIGN — switch in ACTIVE conductor:
  Wall ──[ACTIVE]──[SWITCH]──── Transformer primary ──[NEUTRAL]── Wall
                      │
                   OFF: Active disconnected. Primary at 0V ✓

  COLLINS 516F-2 — switch in NEUTRAL conductor:
  Wall ──[ACTIVE]───────────── Transformer primary ──[SWITCH]──[NEUTRAL]── Wall
              │                         │
          Always live             OFF: current stops, but —
                                  Active still on primary ✗  Fuse on neutral ✗
                                  C15 (active→chassis) always energised ✗

  Wire colours by region:
  Australia/NZ:  Active=brown/red   Neutral=blue/black  Earth=green/yellow
  USA/Canada:    Hot=black          Neutral=white       Ground=green/bare
  UK:            Line=brown         Neutral=blue        Earth=green/yellow
  Europe/Schuko: Live=brown         Neutral=blue        Earth=green/yellow
  Japan:         Hot=black          Neutral=white       (often 2-pin only)
  Brazil:        Phase=brown/black  Neutral=blue        Earth=green/yellow

Figure 1. Switched-neutral architecture and wire colour conventions by region.

The Fuse Is Also on the Wrong Side

The 516F-2 mains fuse is on the neutral side — the same side as the switch. When the fuse blows, the transformer de-energises, but the active conductor is still connected to the fuse holder and all primary wiring. Opening the 516F-2 to replace a blown fuse while the mains plug is inserted means making contact with 230 V, 120 V, or whatever local mains voltage at the fuse holder. Always remove the mains plug before any work inside the 516F-2 — including fuse replacement.

Section 2 — Global Operations — Voltage, Plug Polarity & Wiring Standards by Region

Primary Winding Configuration — Confirm Before Connecting to Mains

  115/120V OPERATION — primary windings IN PARALLEL:
  [Winding 1: green–green] PARALLEL [Winding 2: white–white]
  Combined impedance halved. Supply current: 4 A nominal.
  Remove capacitor C1 if line frequency > 60 Hz.

  230V OPERATION — primary windings IN SERIES:
  [End of Winding 1] → [Start of Winding 2] (green to white junction)
  Combined impedance doubled. Supply current: 2 A nominal.
  Remove capacitor C1 if line frequency > 60 Hz.

  WRONG CONFIGURATION CONSEQUENCE:
  115V winding on 230V mains → transformer core saturates → immediate overheating → failure.
  230V winding on 115V mains → output voltages approximately halved → radio will not operate.

Figure 2. 516F-2 primary winding configuration — 115/120 V vs. 230 V.

Global Operations Reference Table

Detailed Notes by Region

Japan (100 V / 50 or 60 Hz)

Japan is the only country in the world using 100 V as its standard residential mains voltage. The 516F-2’s two primary windings, connected in parallel, are designed for 115 V — operating them at 100 V means the transformer is under-driven by approximately 13%. The secondary voltages will be proportionally lower: LV B+ will be approximately 240 V instead of the specified 275 V, and HV B+ will be approximately 695 V instead of 800 V. The radio will function, but PA output power will be reduced and the bias supply may fall outside its adjustment range. A step-up autotransformer (100 V to 115 V, 500 W minimum) is recommended for Japanese operation.

Regarding the switched-neutral defect: older Japanese outlets (Type A, non-polarised) do not enforce plug orientation, making the switched conductor unpredictable. Newer Japanese outlets are polarised, with the wider slot connected to neutral — identical to the US NEMA convention. Even at 100 V, the shock current through wet skin (1 kΩ) is 100 mA — right at the fibrillation threshold. Japan’s 100 V mains should not be considered safe. The same rules apply: unplug before opening.

United States and Canada (120 V / 60 Hz)

Factory configuration. The NEMA 5-15 polarised plug (wide blade = neutral, narrow blade = hot) provides consistent polarity at correctly wired US outlets — the Collins design relies on this. In a correctly wired and correctly polarised installation, the neutral is reliably switched. However, the active conductor is still permanently connected to the primary, and the defect remains. Non-polarised extension cords, old reversed sockets, and non-polarised adapters all invalidate the polarity assumption.

Modern US mains voltage typically measures 120–126 V rather than the original 115 V design basis. This elevated voltage increases B+ outputs above specification. With tube rectifiers, unloaded LV B+ can exceed 310–360 V at 120 V mains. The Weber K5IU article in The Signal documents these measurements in detail and their effect on aging component stress.³

Brazil (127 V or 220 V depending on city)

Brazil is unique in using two different residential voltages — 127 V in São Paulo, Rio de Janeiro, and parts of the south, and 220 V in Brasília, Belo Horizonte, and the northeast. A 516F-2 operated in Brazil requires voltage verification before connection. The primary wiring must be in parallel for 127 V cities and in series for 220 V cities. The Type N (NBR 14136) plug used since 2011 is polarised, but older Type A or C outlets (still common) are not. Verify the outlet type and polarity before connecting.

United Kingdom and Ireland (230 V / 50 Hz)

The BS 1363 Type G plug provides the best plug-level safety of any region. The plug contains a fuse (typically 3 A or 5 A for low-load equipment) that blows before the mains wiring is overloaded. The plug is polarised — the rectangular Live pin is distinguishable from the Neutral pin by position, and the Earth pin is longer (it opens the socket shutters). The socket is always wired: Live = top-right, Neutral = top-left, Earth = top-centre. UK wiring (BS 7671) requires that single-pole switches interrupt the Line (live) conductor.

Despite the superior plug safety, the switched-neutral defect is fully present once the mains lead enters the 516F-2 chassis. The BS 1363 plug fuse protects the mains lead; it does not protect against the primary-side live conductor being present when the radio appears off.

Continental Europe — Schuko and Type E (230 V / 50 Hz)

This is the most hazardous plug configuration for the switched-neutral defect. The Schuko (CEE 7/4) and Type E (CEE 7/5) plugs are completely non-polarised. Either orientation of the plug in the socket is equally valid, meaning there is no reliable way to predict which of the two mains conductors (Live or Neutral) is connected to which pole of the 516F-2 mains lead. The Collins design assumed the neutral would be consistently on the switched side — this assumption is entirely invalid in Schuko installations.

In any given Schuko installation, the 516F-2 front-panel switch may be breaking either the Live or the Neutral conductor, determined by whichever orientation the mains plug was last inserted. Rotating the plug in the socket reverses the polarity. The switched-neutral defect in a Schuko country is therefore not merely a fixed design limitation — it is a random hazard that changes each time the plug is removed and reinserted.

India, South Africa, Singapore, UK-derived Standards (230 V / 50 Hz)

Countries using BS 1363 (UK, Singapore, Malaysia, Hong Kong, Pakistan, some of the Middle East) or BS 546 variants (India, South Africa, Zimbabwe, Namibia) have polarised plugs with defined Live and Neutral positions. The wiring standards in these countries (IS 732 India, SANS 10142 South Africa, SS 638 Singapore) all require single-pole switches to interrupt the Line conductor. The Collins design does not comply. The same remediation applies as for Australia — the rear-panel double-pole switch or full primary rewire.

Shock Severity — Quantitative Comparison by Voltage

Section 3 — Safety Capacitor Replacement (C15 & C16) — All Regions

Why C15 Is Permanently Energised at All Voltages

C15 connects from the active/hot/live/Line conductor to chassis ground. Because the Collins switched-neutral design leaves the active conductor permanently connected to the primary wiring (regardless of switch position or mains voltage), C15 is permanently energised at full local mains voltage from the moment the mains plug is inserted until it is removed. This is true at 100 V, 120 V, 127 V, and 230 V equally. At 230 V (Australian/UK/European mains) the risk is greatest, but at no voltage is it acceptable.

Y2 Certification — Required Everywhere, Non-Negotiable

Y2-certified capacitors (IEC 60384-14) are engineered to fail open-circuit rather than short-circuit. This is the only acceptable replacement for C15 and C16 at any mains voltage. The Y2 rating includes an AC working voltage specification of 250 VAC, which provides adequate margin above all operating voltages worldwide including 230 V.

Capacitor Positions and Replacement Parts

Global Suppliers

Section 4 — Why Collins Used This Design

The switched-neutral design was common in American commercial and consumer electronics through the 1950s and 1960s. Several factors contributed:

• Single-pole switch economy. Running one switched conductor through the 11-pin power cable required only one switched line. With the US polarised plug enforcing consistent polarity, the neutral would predictably always be on the switched side.
• US wiring conventions of the era. The concept that single-pole switches must interrupt the active/hot conductor was not codified in the NEC until later editions. Switching the neutral was accepted 1950s American industrial practice and Collins was not unusual in adopting it.
• Polarised plugs as mitigation. The US NEMA polarised plug provided partial predictability in the intended operating environment. Collins engineers did not design for worldwide operation with non-polarised Schuko outlets or higher-voltage mains systems.

None of this changes the hazard the design creates for operators operating the equipment outside its original design environment, or who open it for service without understanding which conductors remain live.

Section 5 — Mains Wiring Best Practices — What Good Design Requires

The following principles define correct mains wiring practice and should be applied when modifying the 516F-2 mains input or adding isolation hardware:

Section 6 — Corrective Action — Four Levels

• 1
  Procedural — remove the mains plug before opening the chassis. Always. The only action that removes the active conductor from the 516F-2 interior is physically pulling the mains plug from the wall. This applies at 100 V, 120 V, 127 V, and 230 V, with polarised or non-polarised plugs, in every country. Affix a reminder label to the 516F-2 front panel in your language: “Remove mains plug before opening — switch OFF does NOT isolate.”
• 2
  Replace C15 and C16 with Y2-certified capacitors — do this first, regardless of other work Source from Element14, Mouser, Digi-Key, RS Components, or Farnell. Part: Kemet PHE840MY6100MR17 or EPCOS B32021A3103M. Cost: under the equivalent of AU$10 / US$6 / £5 / €6. Time: 30 minutes. Replace the X-class line-to-line cap at the same time. Verify values from the service manual before ordering.
• 3
  Add a rear-panel double-pole mains isolation switch — strongly recommended for all regions; essential for Schuko countries Retrofit the 516F-2 with an IEC C14 panel-mount combined inlet and double-pole switch. When the rear switch is OFF, both active and neutral conductors are interrupted simultaneously — eliminating both the switched-neutral risk and the polarity-uncertainty risk in non-polarised outlet countries. Recommended part: Schurter DD11 series (IEC C14 inlet + double-pole switch + fuse, one panel cutout). Available from Element14, Mouser, Digi-Key, and RS Components worldwide. This modification involves mains wiring — comply with your local electrical wiring regulations and have the work checked by a licensed electrician.
• 4
  Full primary rewire — switch the active conductor, relocate the fuse to the active side Rewire the 516F-2 internal primary circuit so the front-panel switch interrupts the active conductor and the fuse is on the active side. This brings the design into compliance with NEC, AS/NZS 3000, BS 7671, IEC 60364, and all other major wiring standards. The W0IY Service Bulletin 1 PCB kit implements this correction as part of a complete service update. Documentation: github.com/w0iy/516F-2. For operators not undertaking a full SB-1 upgrade, the rewire can be performed independently using the service manual schematic to identify the switched conductor path. All mains wiring must comply with local regulations.

Region-Specific Recommendations Summary

Section 7 — Affected Equipment