Yaesu FT-101E Series
Failure Prevention Kit — Component & Modification Design

Section 1 — Variant Guide and Community Resources

FT-101E Production Variants

Plug-in Board Complement (FT-101E Late)

Community Resources

Section 2 — Root Cause Failure Analysis

The FT-101E is both a transmitter and a receiver; its failure modes span both sections. The following ten failures account for the overwhelming majority of FT-101E restoration casualties. RL-1 alone explains more FT-101E service problems than any other single component.

• 1
  RL-1 Main Function Relay — The Heartbeat of the FT-101E RL-1 is a 6-pole double-throw relay that routes virtually everything inside the FT-101E: transmit/receive switching, voltage routing to the PA, metering circuit connections, and several ancillary functions. It is described as the “heartbeat” of the FT-101. The original relay (National Electric AE3271, or equivalent by OMRON MH6P or Matsushita AE317160) is no longer manufactured. The contacts develop an oxide film over 50 years that causes intermittent or failed switching: receive drops out after keying (the relay hangs in TX position), transmit has no plate current (relay does not complete the HV path to the PA), or the meter shows incorrect readings. Critical sourcing warning: all currently-available Western replacement relays (Magnecraft, Potter-Brumfield) have their center-row contacts wired 180° differently from the original Japanese relay. Simply fitting a new relay into the socket without rewiring the socket lugs will not work and may damage the transceiver. The rewiring procedure (moving the center-row connections from one side to the other) is documented at foxtango.org. Used original relays are sometimes available on eBay at premium prices. Budget for either relay socket rewiring or a verified used original relay as part of every FT-101E restoration.
• 2
  3SK40 Receive MOSFET — Degraded Front-End Sensitivity The 3SK40 dual-gate MOSFET on the High Frequency Board is the first active device in the receive chain and is described as “the heart of the FT-101’s receive performance” by NW2M. A degraded 3SK40 causes a measurable reduction in receiver sensitivity — typically 3 dB or more, which represents a threshold that NW2M uses as the replacement criterion. In practical terms: a degraded 3SK40 means the noise floor rises, weak signal copy deteriorates, and S-meter readings are low for a given signal strength. The 3SK40 is socket-mounted on the High Frequency Board for easy replacement. It can fail from static discharge (particularly if the antenna was ever connected without ground, or with a lightning event on the antenna system) or from simple aging. Test the receive sensitivity against the Sherwood Engineering standard (0.22 µV for 10 dB S/N in SSB mode); sensitivity significantly below this indicates a suspect 3SK40. Source NOS 3SK40 or a known-good equivalent.
• 3
  HV Filter Capacitors C77/C78 — Risk of Power Transformer Destruction The 600 V PA plate supply filter capacitors C77 and C78 (typically 150 µF / 450 V each, in series) are the highest-consequence aging components in the FT-101E. A depleted C77/C78 allows 120/100 Hz ripple on the plate supply, degrading transmitted audio with power-supply modulation. A short-circuit failure can drive excessive current through the primary winding of the power transformer, destroying it. Replacement power transformers are documented as expensive and difficult to source. Replace C77 and C78 as part of every complete FT-101E restoration. The procedure requires removing the regulator and noise-blanker boards, inverting the chassis, and working with the HV supply completely discharged. Incorrect polarity of the replacement capacitors causes immediate explosive failure.
• 4
  Electrolytic and Mylar Capacitor Aging — Widespread Throughout All Boards The FT-101E contains approximately 65 electrolytic capacitors distributed across all boards. After 50 years, all of these require inspection and most require replacement: they exhibit increased ESR, reduced capacitance, and in severe cases electrolyte leakage (“ballooning” visible as a swollen capacitor top). The VFO regulated supply rail is the most critical single rail affected — ripple on this rail causes direct frequency instability. Additionally, the mylar (polyester film) capacitors in the FT-101E are documented as “almost all splitting open” in a 50-year-old example: the plastic film case physically cracks from aging, although the electrical failure mode varies (some open, some short). Inspect all visible mylar capacitors for split cases and replace them with polypropylene film equivalents.
• 5
  6JS6C PA Tubes Exhausted and R30 Screen Resistor Wrong Value The matched pair of 6JS6C sweep-tube PA finals is the consumable element of the FT-101E. Exhausted tubes cause low or zero transmit output, inability to find a plate-circuit dip, and erratic plate current. Additionally, the screen grid decoupling resistor R30 in the original design is 47 kΩ / 1 W — a value that allows a destructive transient overvoltage on the screen grid when the supply is removed at TX-to-RX transition, causing internal tube flashover. Replace R30 with 470 kΩ / ½ W before any transmit operation. When fitting non-Japanese 6JS6C replacement tubes (NEC/Toshiba is original; GE/RCA/Sylvania have different inter-electrode capacitance), also replace neutralisation capacitor C125 from 100 pF to 10 pF / 1 kV silver mica and re-neutralise the PA. Always replace as a matched pair and never mix tube types in the same socket.
• 6
  C13 and C131 Coupling Capacitors — Catastrophic Driver-to-PA Failure C13 (coupling the driver output to the PA grid network) and C131 are silver mica types located in the high-temperature PA compartment. Their proximity to the 6JS6C tube heaters raises their operating temperature above ambient, accelerating dielectric degradation. A short in either capacitor routes high-voltage supply directly into the driver circuit, causing immediate and usually catastrophic damage. C13 is particularly vulnerable in radios that were used on 11 m CB frequencies at high power levels — described in the community as “11-meter burn.” Replace both with 1 kV silver mica types at the correct values during any complete restoration. Do not substitute ceramic disc or polyester film — the thermal environment will cause premature failure of non-mica types.
• 7
  VFO Temperature Compensation Drift — TX/RX Frequency Offset The FT-101E was among the very few amateur rigs to include adjustable temperature compensation on the VFO — described by Wikipedia as “virtually the only rig that had adjustable temperature compensation in the VFO; when properly adjusted, it is extremely stable.” The ZERO trimmer on the regulator board controls the TX/RX frequency offset (the frequency shift caused by switching from receive to transmit, as the keying voltage changes the VFO operating point slightly). If this trimmer drifts or is knocked out of adjustment, the operator hears a frequency shift on keying. The right-hand trimmer on top of the VFO must never be touched: it was factory-calibrated to compensate for the VFO’s temperature coefficient and touching it will introduce irreversible drift that requires factory-level temperature-test equipment to correct. Only the left-hand VFO trimmer may be adjusted for frequency calibration. The ZERO trimmer is accessible from the regulator board and should be adjusted after all capacitor replacement is complete.
• 8
  Band Switch Multi-Wafer Contact Contamination — Band-Selective Faults The FT-101E band switch is a 12-position rotary switch with 13 wafers (A through M) routing DC supply voltages, oscillator crystals, RF signal paths, and PA high-voltage circuits. It is described in the Fox Tango community as the most mechanically complex component in the radio. The 13 wafer contacts develop oxide film non-uniformly: some positions affect only one function (low TX power on 15 m while 20 m is fine), some affect both transmit and receive on a band, and some affect the metering circuit. DeoxIT D5 on all switch wafer contacts, cycled 20 times through all band positions, is the standard initial treatment. The VFO rotor wiper contacts on the main tuning capacitor should be cleaned simultaneously — these are documented as a primary cause of VFO instability in aged examples.
• 9
  Pi-Network Coil Burned Connections — Band-Specific Low Power The output pi-network tank coil connections underneath the coil assembly develop heat-stressed solder joints from 50 years of transmit cycles. A high-resistance joint in the pi-network produces reduced power output on the specific band(s) using that coil section while adjacent bands are unaffected. Inspect all pi-network coil connections for discolouration, oxidised solder, or burned insulation. Re-solder any suspect joint with the HV completely discharged. These connections carry RF at up to 130 W and must be clean, well-filled solder joints.
• 10
  Power Transformer Failure — The Most Expensive Casualty Power transformer failure is documented as “fairly common” in the FT-101 series by community experts — specifically shorted primary windings in FT-101EE and other variants. The transformer is destroyed by: running AM at excessively high carrier power (a fully modulated 30 W AM carrier contains 120 W of RF envelope — the maximum safe AM carrier for the FT-101E is 30 W, never 100 W AM); allowing the HV capacitors C77/C78 to fail with the transformer unprotected; or prolonged operation with mis-tuned finals (high SWR). Replacement transformers are expensive and difficult to source. Prevention is the only practical strategy: never exceed 30 W carrier on AM; always tune into a dummy load with quick dip-and-load procedure; always address C77/C78 before sustained operation.

Section 3 — Kit Component Reference

Section 4 — Pre-Operational Safety Protocol

Visual Inspection Checklist

• AC voltage tap: verify the rear-panel power connector jumpers are set for your local supply (100/110/117 V options) before any connection to mains. Incorrect tap setting over-voltages every supply rail including the 600 V HV.
• C77/C78: inspect for swelling or electrolyte seepage with power off. Any sign of distress: replace before power-up.
• R30 value: measure with DMM (power off). If approximately 47 kΩ: must be replaced before transmit operation.
• C13/C131: inspect for burn marks or discolouration. Any visible damage: replace before transmit operation.
• 6JS6C tubes: check for cracked envelopes, darkened plate structures, or loose top-cap connections.
• 11-metre modifications: check whether any crystals or wiring have been modified for CB frequencies. A modified FT-101E may have band segments altered from the factory configuration, requiring additional alignment attention.

Section 5 — Circuit Modifications

Section 6 — Installation Sequence

• 1
  Documentation, variant identification, and AC tap verification Download the FT-101E service manual from foxtango.org. Identify your exact subtype from serial number and board complement. Verify AC voltage tap on the rear power connector. Check for 11-metre modifications. Photograph the interior before touching anything.
• 2
  Visual inspection: C77/C78, C13/C131, R30, 6JS6C tubes Inspect HV capacitors, coupling capacitors, screen resistor value, and PA tubes with power off. Address any findings before power-up.
• 3
  R30 replacement (K-005) and C13/C131 replacement (K-004) Replace R30 (47 kΩ → 470 kΩ) and C13/C131 with 1 kV silver mica. Safety-critical; must be done before any transmit testing.
• 4
  Replace C77/C78 (K-002, MOD-2) Discharge HV, remove regulator and noise blanker boards, photograph and note polarity, replace with 105°C / high-ripple units. Verify correct polarity before re-assembly.
• 5
  Clean all edge connectors, RL-1, band switch, pots, and VFO wipers (K-003, K-009, MOD-1) Remove all boards; clean edge connectors. Clean RL-1 contacts. Clean band switch wafers. Clean all pots and VFO variable capacitor rotor wipers. Re-seat all boards.
• 6
  Replace all electrolytics and mylar capacitors (K-006) Replace all ~65 electrolytic capacitors and all split mylar/polyester film capacitors. Regulator board electrolytics are highest priority within this group. Work board by board; reinstall each before moving to the next.
• 7
  First isolation transformer + Variac power-up and supply rail verification Raise from 0 to full mains over 15–20 minutes. Verify HV at the rectifier board test point (approximately 600 V DC). Verify all regulated rails. No burning smell or smoke.
• 8
  Test 3SK40 receive MOSFET (K-007) Measure receive sensitivity or test 3SK40 HFE on a component tester. Replace if degraded beyond 3 dB from specification. Use ESD precautions.
• 9
  Fit PA tubes (K-008), verify C125 value, and neutralise PA (MOD-2) Determine tube origin (Japanese vs non-Japanese) and set C125 accordingly. Fit tubes as a matched pair. Perform cold-cathode neutralisation. Set bias to 60 mA idle current.
• 10
  VFO ZERO calibration (MOD-3) and full alignment Allow 30-minute warm-up. Adjust ZERO VR for zero TX/RX offset. Perform full alignment: crystal trimmers per band, IF alignment, preselector tracking, transmit output alignment. Record all-band power output and receive sensitivity. Check pi-net coil connections (K-010).
• 11
  Spurious emission check and trap alignment (MOD-4) Verify spectral purity at full power on 10 m and other bands. Adjust traps as needed. Observe 160 m plate current limit. Confirm no 11-metre conversion artefacts on 10 m.

Section 7 — Verification Tests

RL-1 T/R Switching Verification

Receive Sensitivity Verification

PA Idle Current and Neutralisation

TX/RX Frequency Offset