Yaesu FT-101EE Transceiver
Failure Prevention Kit — Component & Modification Design

Section 1 — What the FT-101EE Is and How It Differs

The EE Distinction

Plug-in Board Complement (FT-101EE)

Community Resources

Section 2 — Root Cause Failure Analysis

The FT-101EE shares every failure mode with the FT-101E with the same priority ranking. Each failure mode is described below in terms of the FT-101EE’s specific context where relevant.

• 1
  RL-1 Main Function Relay — The EE’s Dominant Failure RL-1 is the 6-pole relay that routes virtually every functional path inside the FT-101EE: transmit/receive antenna switching, HV supply path to the PA, metering circuit connections, and ancillary switching. It is the single most-discussed failure component in the entire FT-101 series. The original Japanese relay (National Electric AE3271) has been out of production for decades. Contacts develop an oxide film that causes the relay to hang in transmit position after keying, drop receive when first keyed, or fail to complete the HV circuit to the PA. Community evidence from the WorldwideDX and Fox Tango forums consistently confirms that RL-1 is the first item to suspect when the FT-101EE receives but does not transmit, or loses receive after keying. Western replacement relays (Magnecraft, Potter-Brumfield) have contacts wired 180° differently from the original Japanese relay. Installing a Western relay without rewiring the socket will not work correctly and will produce fault patterns identical to a failed original relay. The Fox Tango website provides the complete socket rewiring procedure. Budget for a used original Japanese relay or the socket rewiring work for every FT-101EE restoration.
• 2
  Burned PA Screen Grid Resistors — EE-Documented Failure In the WB4IUY FT-101EE overhaul, the PA screen grid circuit resistors were found burned — photographically documented as visibly damaged in the PA cathode and grid circuit area. This is the physical consequence of the design weakness documented throughout the FT-101 series: screen grid resistor R30 in the original design is 47 kΩ / 1 W, a value too low to prevent a destructive screen-grid voltage transient when the TX supply is removed at TX-to-RX transition. The screen resistor and adjacent grid circuit power resistors absorb this energy over thousands of keying cycles, discolouring and eventually burning open. WB4IUY’s standard EE overhaul procedure includes replacing all power resistors in the PA cathode and grid circuits. The key correction is R30: replace with 470 kΩ / ½ W before any transmit operation. Inspect all PA cathode and grid circuit power resistors for discolouration or carbonisation and replace any suspect units.
• 3
  HV Filter Capacitors C77/C78 — Mandatory Replacement to Protect the Transformer C77 and C78 (each approximately 150 µF / 450 V, in series forming the ~600 V PA plate supply filter) are a mandatory replacement in any FT-101EE of unknown history. These capacitors age in two ways relevant to the EE: first, normal electrolytic degradation (increased ESR and ripple on the HV supply); second, potential catastrophic short-circuit failure that can drive excessive current through the power transformer primary, destroying the transformer. Replacement power transformers are expensive and difficult to source. The WB4IUY overhaul narrative specifically documents C77/C78 as the first priority replacements made, noting that the new HV capacitors are approximately one-quarter the physical size of the originals despite higher capacitance and voltage ratings — a useful marker that confirms the originals are definitively superseded by modern components. Replace with 105°C / high-ripple units at the correct values. Correct polarity is mandatory: reversed polarity causes immediate explosive failure.
• 4
  ~65 Electrolytic Capacitors Throughout All Boards — Systematic Replacement The WB4IUY FT-101EE overhaul specifically confirms the electrolytic capacitor count as approximately 65 units spread across all boards. After nearly 50 years, these are uniformly degraded in ESR and capacitance and should be systematically replaced in a complete overhaul. WB4IUY’s approach — working board by board, rebuilding and testing each before reinstalling — is the recommended method. Some electrolytic capacitors are on terminal boards rather than plug-in boards, described as “not easy to get to.” The grey-coloured mylar (polyester film) capacitors found on many boards are also documented as physically splitting open with age — inspect all film capacitors for cracked or peeling outer sleeves and replace with polypropylene film types. The VFO regulated supply electrolytics are the highest-priority group: ripple on this rail causes direct VFO frequency instability.
• 5
  Driver Coupling Capacitor (C13) — Mandatory Silver Mica Replacement WB4IUY’s standard FT-101EE overhaul protocol specifically includes the “driver coupling cap mod” as a named standard step — replacing the coupling capacitor between the driver stage and the PA grids with a high-quality silver mica unit. The original driver coupling capacitor C13 sits in the high-temperature PA compartment where proximity to the 6JS6C heaters accelerates dielectric ageing. A short circuit in C13 applies grid or plate voltage directly to the driver output in a configuration not designed for it, producing immediate and catastrophic damage. The C13 failure is commonly called “11-meter burn” in the community — radios operated on CB frequencies at high power place disproportionate stress on this capacitor by running high current at the driver output continuously. Replace C13 (and C131 if accessible) with 1 kV silver mica at the correct value. Do not substitute ceramic disc or polyester film types in the hot PA compartment environment.
• 6
  6JS6C PA Tubes Exhausted — Matched Pair with C125 Verification The 6JS6C sweep-tube finals are consumable items in the FT-101EE. Exhausted tubes cause low or zero transmit output power, inability to achieve a clean plate circuit dip, or erratic plate current readings. When replacing PA tubes, the critical question is tube origin: the original NEC or Toshiba Japanese 6JS6C tubes have different inter-electrode capacitance from US-manufactured equivalents (GE, RCA, Sylvania). Fitting non-Japanese tubes without also changing C125 (the series neutralisation capacitor, from 100 pF to 10 pF / 1 kV silver mica) results in incorrect neutralisation, potential self-oscillation on the upper bands, and premature tube failure. Always replace as a matched pair; never mix tube types between the two sockets. Perform cold-cathode PA neutralisation after any tube or C125 change.
• 7
  3SK40 Front-End Receive MOSFET — Sensitivity Degradation The 3SK40 dual-gate MOSFET on the High Frequency Board is the first active device in the receive chain, socket-mounted for replacement, and identified by NW2M as “the heart of the FT-101’s receive performance.” A degraded 3SK40 produces a measurable reduction in receiver sensitivity — the community standard replacement threshold is approximately 3 dB of degradation from specification. In practical terms: the noise floor rises noticeably, weak signals that were previously copyable become difficult to read, and S-meter readings for a given signal level are lower than expected. Handle the 3SK40 with ESD precautions. Test by substituting a known-good 3SK40 or equivalent and comparing receive sensitivity. Always test sensitivity before performing a full alignment, as a degraded MOSFET will cause alignment results to fall short of the specification regardless of other adjustments.
• 8
  Band Switch and VFO Rotor Wiper Contamination — Band-Selective Faults The FT-101EE band switch has 13 wafers (A through M) routing supply voltages, oscillator crystals, RF signal paths, and PA high-voltage circuits. WB4IUY’s documented EE overhaul specifically includes “spray and clean all wafers of the band switch assembly” and VFO variable capacitor rotor wiper cleaning as standard steps. The oxide contamination is non-uniform across the wafers, which is why specific bands fail while others operate normally. Wafer contamination affecting the HV routing wafers can cause the PA to have no plate current on certain bands while adjacent bands transmit normally — a misleadingly specific symptom that looks like a crystal or alignment problem but is actually a switch contact issue. Clean all wafers with DeoxIT D5; cycle the band switch through all positions a minimum of 20 times after application.
• 9
  VFO Temperature Compensation ZERO Trimmer Drift — TX/RX Frequency Offset The FT-101EE VFO incorporates adjustable temperature compensation — factory-set via the right-hand trimmer on top of the VFO unit. This right-hand trimmer must never be touched: it was calibrated at the Yaesu factory to the thermal characteristics of the specific VFO coil and temperature compensation components in that individual unit, and adjusting it without a temperature-controlled test environment will introduce permanent drift that cannot be corrected without factory-equivalent equipment. The ZERO VR on the regulator board controls the TX/RX frequency offset (the frequency shift heard on pressing PTT). After any capacitor replacement on the regulator board: verify the ZERO VR is correctly set by monitoring VFO frequency through PTT transitions. An offset greater than 5 Hz should be corrected by adjusting the ZERO VR only.
• 10
  Pi-Network Coil Connections and Power Transformer — Long-Term Stress Failures Two failure modes share the tenth position because they represent the highest-consequence long-term stress failures in the FT-101EE. Pi-network coil connections develop burned or high-resistance solder joints from 50 years of transmit cycles, causing band-selective low power output. Inspect all pi-net coil connections underneath the tank coil for discolouration and re-solder as needed with HV discharged. Power transformer failure — documented as “fairly common” across the FT-101 series — results from three causes, all preventable: operating AM above 30 W carrier power (a 30 W carrier with full modulation = 120 W envelope, the supply limit); allowing C77/C78 to fail; and prolonged mis-tuned operation at high SWR. The power transformer is the most expensive and most difficult component to source as a replacement. Preventive operation limits are the only practical protection.

Section 3 — Kit Component Reference

Section 4 — Pre-Operational Safety Protocol

Visual Inspection Checklist

• AC voltage tap: verify the rear power connector jumpers are set for your local mains supply (100/110/117 V AC). Incorrect setting over-voltages every rail including the 600 V HV.
• C77/C78 physical condition: inspect for swelling or electrolyte seepage with power off. Any distress: replace before power-up.
• R30 value: measure with DMM (power off). If approximately 47 kΩ: must be replaced before transmit operation.
• PA cathode and grid resistors: inspect for discolouration or physical burning. Any burned appearance: replace before transmit operation.
• C13/C131: inspect for burn marks, discolouration, or split bodies. Any visible damage: replace before transmit.
• Speech processor slot: confirm whether a processor board is fitted or absent. If absent: this is normal for the EE and does not require correction.
• 11-metre modifications: check whether band positions or crystals have been modified for CB use. A modified EE may have band coverage altered from factory configuration.

Section 5 — Circuit Modifications

  PA SCREEN RESISTOR CORRECTION — EE-DOCUMENTED FAILURE (WB4IUY)

  SYMPTOM: Burned/carbonised resistors photographically confirmed in PA
           cathode and grid circuit area of FT-101EE units.
  CAUSE:   R30 = 47kΩ / 1W (original) allows screen voltage transient
           at TX-to-RX transition → repeated flashover events
           → accumulated thermal stress → burned resistors.

  CORRECTION:
    R30 original:  47kΩ  / 1W  ← REPLACE before any transmit operation
    R30 corrected: 470kΩ / ½W  ← prevents screen transient flashover

  ALL PA cathode and grid circuit power resistors should be inspected
  during overhaul and any showing discolouration or carbonisation replaced.
  (Reference: WB4IUY FT-101EE overhaul, photographically documented)

  C125 SELECTION (neutralisation series capacitor):
    Original NEC/Toshiba 6JS6C tubes → C125 = 100pF / 1kV silver mica
    Non-Japanese 6JS6C tubes         → C125 = 10pF  / 1kV silver mica
    (Wrong value causes incorrect neutralisation and premature tube failure)

Figure 1. PA screen resistor correction and C125 neutralisation capacitor selection guide.

Section 6 — Installation Sequence

• 1
  Documentation, variant identification, and pre-work photography Download the FT-101EE service manual from foxtango.org. Identify board complement and serial number subtype. Verify AC voltage tap. Photograph complete interior. Note presence or absence of speech processor board slot (absent = normal for EE).
• 2
  Visual inspection: C77/C78, R30, PA resistors, C13/C131, tubes Inspect all items with power off and HV discharged. Address all pre-power findings before any mains connection.
• 3
  R30 correction and PA cathode/grid resistor replacement (K-003) Replace R30 (47 kΩ → 470 kΩ). Replace any burned or discoloured PA cathode and grid circuit power resistors. Safety-critical; mandatory before transmit.
• 4
  C13/C131 driver coupling cap replacement (K-004) Install driver coupling cap mod per WB4IUY EE overhaul standard protocol. Silver mica 1 kV at correct value. PA compartment: HV discharged.
• 5
  Replace C77/C78 (K-002, MOD-2) Full HV discharge procedure. Remove regulator and blanker boards. Photograph polarity. Install with correct polarity. Verify before re-assembly.
• 6
  Clean edge connectors, RL-1, RL-2, band switch, pots, and VFO wipers (K-005, K-009, K-010) Working systematically: remove all boards, clean edge connectors; clean RL-1 contacts (paper + DeoxIT); disassemble and clean RL-2; clean all band switch wafers; clean all pots; clean VFO rotor wipers. Re-seat all boards.
• 7
  Systematic electrolytic and film capacitor replacement (K-006) Work board-by-board replacing all ~65 electrolytics and all split film capacitors. Rebuild each board; test-fit and verify before moving to the next. Note: some capacitors are on terminal boards, not plug-in boards, and are “not easy to get to” (WB4IUY).
• 8
  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 (~600 V). Verify all regulated rails. No burning smell; no smoke.
• 9
  3SK40 MOSFET test (K-007) and PA tube verification (K-008) Test receive sensitivity for 3SK40 degradation; replace if below threshold. Verify 6JS6C tube origin; set C125 accordingly; fit as matched pair. Neutralise PA (MOD-2). Set bias to 60 mA.
• 10
  ZERO trimmer calibration (MOD-3) and full alignment 30-minute warm-up. Adjust ZERO VR for <5 Hz TX/RX offset. Full alignment: crystal trimmers per band, IF alignment, preselector tracking, transmit output. Record all-band power and receive sensitivity.
• 11
  Spurious emission check and dial lamp replacement (MOD-4, K-010) Verify spectral purity on 10 m; adjust traps as needed. Replace VFO and S-meter dial lamps as a matched pair. Final performance documentation.

Section 7 — Verification Tests

RL-1 T/R Dropout Test

PA Screen Grid Resistors and Idle Current

Receive Sensitivity

TX/RX Frequency Offset