Electrically identical but 4-pin UX4 base — not pin-compatible with Octal
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
Directly heated (filament cathode) — the filament IS the cathode. Observe heater warm-up time before applying B+ to protect the tube and filter capacitors.
Electrically identical to the older 4-pin Type 80 tube but with an Octal base — not pin-compatible.
6087 is an indirectly heated drop-in replacement with slightly different warm-up characteristics (slower soft start). 6106 (Bendix) is a ruggedized military version (5Y3WGT).
Russian 5Ц4С (5C4S) is a functional substitute but may produce slightly higher output voltage than NOS 5Y3 types.
Relatively high internal resistance causes significant voltage sag under load — a characteristic valued in guitar amplifier designs for natural compression. The RCA datasheet does not state an explicit Vdrop figure; the 60 V value is an approximation at 125 mA from a rectifier comparison table. Actual drop varies widely with load current due to the high internal resistance.
Max first filter capacitor is 20 µF with capacitor-input filter. Exceeding this risks excessive peak plate current on the directly heated cathode.
Pin Layout — Octal
1No Connection
2Filament
3No Connection
4
Socket-Compatible Tubes ⚠ Not electrically compatible