RCAData: HighHigh quality — base, heater, all universal parameters present, and ≥50% of desirable parameters filled in. Safe to use for design decisions.
Indirectly heated rectifier on same Octal base but higher voltage rating (500V RMS vs 350V) and different pinout — not a drop-in
5Y3GT
Same electrical ratings but directly heated (filament cathode) — same Octal base but different construction. The 5Y4G has slower warm-up due to indirect heating.
Electrical Specifications
Absolute Maximum
Anode Voltage (max)AC Voltage per Plate (max RMS)350V
Rectifier
Peak Inverse VoltagePeak Inverse Voltage1,400V
Voltage Drop (typical)Voltage Drop (at 125 mA DC)60V
Max C-input Filter CapacitorMax C-input Filter Capacitor20µF
Notes
Indirectly heated rectifier — unlike the directly heated 5Y3, the 5Y4G has a separate cathode heated by the filament. This provides a natural delay before the tube conducts, protecting filter capacitors.
RCA datasheet states 'The 5Y4-G is the same as the 5Y3-G except for the following items' — mechanically different (indirectly heated) but same electrical ratings.
5Y4-G has pin 5 = Plate No.1, pin 3 = Plate No.2. The 5Y4-GT variant uses a different pinout: pin 3 = Plate No.2, pin 5 = Plate No.1.
The 5Y4-GT uses a 6-pin intermediate-shell Octal base (JETEC B6-8L or B6-48).
Raytheon lists 5V4G, 5Y3GT, 5W4GT as substitutes — verify ratings and pinout before substituting.