Yaesu FT-200 / FT-250 / Tempo One
Failure Prevention Kit — Component & Modification Design

Section 1 — Variant Guide and Community Resources

FT-200 Variants and Accessories

Tube Complement

Community Resources

Section 2 — Root Cause Failure Analysis

The FT-200 is an all-valve design from approximately 1969. Its failure modes span genuine tube aging and scarcity problems, a critical solid-state component in the VFO regulator, and mechanical contact degradation in the relay and potentiometer sections.

• 1
  7360 Balanced Modulator Tube — The Rarest Tube in the FT-200 The V4 7360 beam deflection tube is the heart of the FT-200’s SSB generator. The 7360 operates as a variable-mu push-pull balanced modulator, producing the double-sideband suppressed-carrier signal that the 9 MHz crystal filter converts to single-sideband. Without a functional 7360, the FT-200 cannot generate a clean SSB signal at all. VK2YLD’s restoration confirms: the 7360 tube was “really muddy sounding, and the modulator balance was dipping but couldn’t get proper carrier null,” indicating internal element degradation rather than a simple adjustment problem. New production 7360 tubes have been unavailable for decades. NOS examples are available but scarce and expensive. A solid-state replacement circuit that plugs directly into the 7360 socket is documented in the FT-200 community; this is the practical long-term restoration solution. The 6JH8 beam deflection tube is similar in principle but has a different pin configuration and requires socket adaptation. Before purchasing an FT-200 for restoration: source at least one spare 7360 or the solid-state replacement board.
• 2
  VFO Regulator Transistor Drift — Frequency Instability from Voltage Rail Collapse The FT-200 uses a solid-state VFO operating at 5–5.5 MHz, regulated to approximately 9 V DC for temperature stability. This is a transistor-regulated supply using two BJTs — the first as the regulating element and the second as the control element. VK2YLD documents extensive drift in this regulator: “After 30 mins warm-up, the voltage was set at 9.00 V. After a while, it had moved to 8.7 V. Letting the set cool down then powering on again, it measured 10.6 V and slowly fell as the radio warmed.” This voltage swing is directly responsible for the FT-200’s reputation for VFO drift until warm. VK2YLD’s solution: replace the two original BJT transistors with a 7805 voltage regulator IC, with the “Adjust” terminal spanning to the original adjust potentiometer. “Also changed all the resistors in the regulator as the whole lot were out of tolerance.” Result: a stable, temperature-independent 9 V rail. This modification should be considered for every FT-200 restoration.
• 3
  Transmit Relay Contact Burn — Intermittent or Failed TX/RX Switching The TX/RX antenna relay in the FT-200 routes the antenna from the receive RF input to the transmit PA output on keying. VE3NCQ’s restoration documents this failure directly: “The transmit relay was pretty burned, so I swapped it with the VOX relay.” After 55 years of use, the silver contacts develop a layer of oxidised silver sulphide that causes high-resistance, intermittent, or completely failed contact closure. Symptoms: no transmit output with all other circuits apparently functioning; intermittent TX/RX switching; receive dropout on keying. The relay can sometimes be restored by cleaning contacts with a solvent-dampened strip of card stock (no abrasives); if the contacts are physically burned through or pitted: the relay requires replacement. Modern relay types compatible with the FT-200 socket pinout can be sourced; verify coil voltage and contact current rating before fitting a substitute.
• 4
  Tone Oscillator Transistor Bias Drift — No Tune Signal or Intermittent CW Sidetone The FT-200 uses a solid-state tone oscillator (TR503 in the schematic) operating at 1500 Hz to provide the TUNE signal applied to the balanced modulator, and also the CW sidetone. VE3NCQ documents this failure: “The tone oscillator was intermittent, which turned out to be a misadjusted transistor bias control.” After 55 years, the bias potentiometer and resistors in the tone oscillator circuit drift from their original values, taking the transistor out of its correct operating class. Symptoms: no output from the tone oscillator, causing the TUNE function to produce no signal (making PA alignment impossible), or intermittent sidetone. Inspect and measure all resistors in the tone oscillator circuit; clean the bias pot with DeoxIT D5; set the transistor operating point per the service manual.
• 5
  Balanced Modulator Carrier Null Off — Carrier in the Sideband Signal The 7360’s balanced modulator is adjusted for maximum carrier suppression by balancing the push-pull circuit. If the balance control has drifted (or the 7360 has aged non-symmetrically), excessive carrier passes through the sideband filter, producing a dirty transmitted signal. VE3NCQ confirms this is a typical finding: “I had to connect the scope and fix the balanced modulator since too much carrier was present.” Carrier in the output produces a signal with a “buzz” or “heterodyne” quality that is immediately obvious to stations receiving it. The balance adjustment is via a potentiometer accessible with covers in place. Set for minimum carrier output as monitored on an adjacent receiver, with the carrier oscillator running but no audio input. This adjustment must be re-checked after any work on the 7360 or surrounding circuit.
• 6
  Power Supply B+ Out of Specification — Incorrect Voltage Stresses All Stages The FT-200 requires B+ of approximately 300 V DC at the correct current capacity from its external or internal supply. The Antique Radio Forums document the FP-200 compatibility issue: an HP-23A Heathkit supply produces a B+ significantly higher than specification, which stresses all valve stages. The correct nominal B+ is stated in the service manual; operating the FT-200 consistently above specification accelerates ageing of all valve stages and reduces tube life. For 220/240 V markets, an additional series transformer or Variac is sometimes required to drop the primary voltage before the existing supply transformer, as documented in detail in the Antique Radio Forums. Always verify B+ with a calibrated meter at the supply output before connecting the FT-200.
• 7
  6JS6A PA Finals Exhausted — Accessory Socket Heater Link Critical The 6JS6A PA finals (V6/V7) age and exhaust over decades of service. Symptoms: low transmit power, inability to achieve a clean plate dip, erratic plate current, or no transmit output. However, before suspecting tube failure, the accessory socket bridge must be verified: the FT-200 manual explicitly states the 6JS6A heater voltage is supplied through pins 1 and 2 of the accessory socket. If this bridge is absent (radio acquired without its original accessory cable), the PA heaters will be cold and there will be no transmit output from the finals regardless of tube condition. After verifying the heater link: test the 6JS6A tubes on a suitable tube tester or substitute with known-good units. VK2YLD documents the 6DQ5 TV sweep tube as a near pin-compatible substitute with an octal adapter rewire, noting the inter-electrode capacitances are “a near perfect match for 6JS6s right down to the inter-electrode capacitances.” Standard 6JS6A and 6JS6C sources should be checked before attempting substitution.
• 8
  Signal Valve Aging — V2, V3, V5, V9 and Audio Chain The FT-200’s small signal valves degrade progressively over 55 years of standby/operating time. VE3NCQ documents replacing the 12AU7 (V9 relay control), 6BZ6 (V2 RF amp / V8 VOX amp), and 6AV6 (audio chain) as a matter of course. The 6BZ6 (V2) directly affects receive sensitivity; a degraded V2 produces the same symptoms as a misaligned preselector. The 12AU7 (V9) affects the transmit relay driver, and a weak V9B will cause the relay to fail to fully actuate, producing a symptom identical to a defective relay. The 12BY7A driver (V5) failure causes complete loss of transmit drive to the finals, producing an S-meter that reads normally on receive but zero transmit power. Test all small valves on a valve tester or by substitution before attempting alignment or fault diagnosis.
• 9
  Electrolytic Capacitors in Power Supply and Audio Sections — Age Failures The FT-200’s power supply and audio circuits use electrolytic capacitors that are now 50+ years old. VK2YLD documents replacing “some new caps in the power module” as part of the restoration. Power supply filter capacitors degrade with increased ESR, introducing ripple on the B+ rail that modulates the transmitted signal (“hum modulation” on SSB, a characteristic 100/120 Hz buzz in the transmitted audio). Audio coupling capacitors dry out, producing reduced bass response and distorted audio. The B+ filter electrolytic on the external power supply is particularly important: if this capacitor develops a partial short, it can draw excess current and potentially fail the supply rectifiers. Replace all electrolytic capacitors in the power supply (wherever located) and audio sections as part of any complete FT-200 restoration.
• 10
  Potentiometer and Switch Contact Oxidation — Band-Selective Faults and Noise The FT-200’s carbon-track potentiometers and rotary switch contacts have been idle for decades in most examples. Oxidised pot tracks produce scratchy audio and noisy AGC, intermittent signals at extreme pot settings, or completely open circuits at one end of the audio range. The band switch contacts develop oxide film causing band-selective faults on receive and transmit. The AFC control, MIC GAIN, RF GAIN, and audio controls are all carbon-track types. DeoxIT D5 applied generously with the control rotated back and forth 20 times is the standard treatment. The band switch wafers require careful application of DeoxIT with a fine-tip applicator, cycling through all band positions. VK2YLD documents having to rip out and replace the MIC GAIN pot as a switch-pot (a dual-function modification that also switches the PA heater supply for receive-only monitoring).

Section 3 — Kit Component Reference

Section 4 — Pre-Operational Safety Protocol

Visual Inspection Checklist

• Accessory socket: verify pins 1 and 2 bridged before connecting power supply.
• Aux VFO socket: verify shorting plug fitted.
• 7360 tube (V4): inspect for internal element damage, getter flash missing, or cracked envelope. Test for carrier suppression before undertaking any other alignment.
• PA tubes V6/V7: inspect for cracked envelopes, darkened getters, or loose top-cap connections.
• Power supply: inspect all electrolytic capacitors in the supply for bulging, leakage, or discolouration before energising.
• Transmit relay: inspect relay contact appearance through any inspection opening. Brown/black discolouration indicates burned contacts requiring treatment before transmit testing.
• All valves: reseat all valves in their sockets by gentle removal and re-insertion to clean the socket contacts before first power-up.

Section 5 — Circuit Modifications

  FT-200 VFO REGULATOR MODIFICATION — VK2YLD METHOD

  PROBLEM:
  Original BJT regulator transistors drift with age
  → VFO rail: 10.6V cold → 8.7V warm (1.9V swing)
  → VFO oscillator frequency drifts as rail voltage changes
  → Radio must warm up 30+ minutes before frequency settles

  SOLUTION:
  Replace first BJT (series pass) with 7805 IC
  Bridge 7805 ADJ/GND terminal to second transistor base
  (picks up original adjust pot voltage reference)
  Replace ALL resistors with 1% metal film at correct values

  RESULT:
  VFO rail: 9.00V ± 0.05V cold through full operating temperature
  Frequency stability improved from 30-minute warm-up to
  approximately 5-minute warm-up for commercial operations

  Note: The accessory socket heater link (pins 1 and 2)
  is the #1 cause of "no transmit" on a freshly
  acquired FT-200. Always check this before
  assuming any circuit fault. See K-001.

Figure 1. FT-200 VFO regulator modification summary and accessory socket note.

Section 6 — Installation Sequence

• 1
  Documentation, tube inventory, and 7360 sourcing Download the FT-200/250 service manual from BAMA or foxtango.org. Identify all tube types present. Source a tested 7360 NOS tube or the solid-state replacement before beginning any work. Verify accessory socket bridge (pins 1&2) and Aux VFO shorting plug.
• 2
  Power supply inspection and electrolytic replacement (K-005) Remove all electrolytic capacitors from the power supply (FP-200 or internal supply if fitted). Replace with 105°C high-ripple types. Verify B+ voltage under load before connecting to the FT-200.
• 3
  VFO regulator upgrade (K-004, MOD-1) Replace VFO regulator BJTs and resistors with the 7805 IC method. Verify stable 9.0 V across the full temperature range before proceeding.
• 4
  Valve reseating, transmit relay cleaning, pot and switch cleaning (K-003, K-009) Reseat all valves. Clean transmit relay contacts. Apply DeoxIT D5 to all pots and band switch wafers. Replace audio and bias electrolytics throughout the chassis.
• 5
  Tone oscillator restoration (K-008) Replace tone oscillator resistors. Clean bias pot. Verify 1500 Hz output in TUNE mode before any PA testing.
• 6
  First Variac power-up and B+ verification (K-010) Raise from 0 to full mains over 10–15 minutes. Verify B+ at correct specification. Verify VFO rail at stable 9.0 V. Verify all valve filaments glowing. Verify receive audio.
• 7
  Small valve test and V4 (7360) test (K-006, K-002) Test all small signal valves. Test 7360 by monitoring carrier suppression on an adjacent receiver. Replace any weak valves or install solid-state 7360 replacement (MOD-2).
• 8
  6JS6A PA tube test and neutralisation (K-007, MOD-3) Test or substitute 6JS6A PA finals. Verify accessory socket bridge for heater voltage. Neutralise PA per service manual procedure with cover in place, non-metallic tool. Set bias to 60–65 mA idle.
• 9
  Balanced modulator null and full alignment (MOD-4) Null balanced modulator for minimum carrier. Align IF transformers. Align preselector on each band. Calibrate VFO scale. Verify full power output on all bands.
• 10
  On-air verification and performance documentation Make a CW test transmission on a calibrated dummy load. Verify power output. Have an adjacent operator verify audio quality — no buzz, no carrier, clean SSB. Record all-band power and receive sensitivity baseline.

Section 7 — Verification Tests

Accessory Socket and PA Heater Verification

VFO Regulator Stability

7360 Carrier Suppression

PA Power Output and Neutralisation