5R4

5R4 identifies a family of full-wave vacuum rectifiers documented in several glass versions, including 5R4-GY and 5R4WGB. Two anodes work with a common directly heated filament, nominally 5 V at 2 A. In the consulted sheets anodes are on octal pins 4 and 6, filament on 2 and 8. The circuit rectifies both halves of a voltage supplied by a centre-tapped secondary. Since the filament is also the cathode, its supply must be considered together with the high-voltage circuit and the DC take-off point.

Family ratings depend on version and filter. RCA’s September 1948 5R4-GY sheet separates combinations of inverse voltage, DC current and operating altitude. The column for 2800 V no-load peak inverse voltage, intended for altitudes up to 20,000 feet, gives 150 mA DC with capacitor-input filtering or 175 mA with choke input. Permitted peak anode current is instead 650 mA per anode, not the DC current available to the load. Other columns have different conditions and cannot be combined into one performance claim using the most favorable maxima.

The first filter component also changes supply behavior. With capacitor input, the capacitor recharges through current pulses; RCA uses 4 µF examples and ties performance to effective supply impedance per anode. It warns that increasing capacitance may require higher impedance to keep peak current within its limit. Curves also distinguish regions allowing simultaneous filament and anode-voltage application from regions requiring filament preheating. A directly heated filament therefore does not make all starting conditions identical.

Tung-Sol describes the 5R4WGB in tentative data of 1 December 1958 as a ruggedized version with additional controls. One capacitor-input example uses 700 V RMS per anode, 4 µF and 100 Ω supply impedance per anode, giving 275 mA DC, about 730 V output at full load and 800 V at half load. Filter values refer to the document’s 60 Hz operation. The rating table also specifies 10 seconds of preheating for the stated conditions; curves distinguish regions allowed without preheating. These data belong to the WGB and do not automatically transfer its limits to other 5R4 versions.

WGB construction notes explain the ruggedized version well. Tung-Sol describes a hard-glass bulb supported in a skirted base by resilient silicone rubber, isolating the valve from shock even with the base clamped to the chassis. It cites magnified inspection of every tube’s welds, electrical stabilization through repeated cold starts and sample testing by lot. Tests cover low pressure, shock, fatigue and filament cycling; the latter includes 2000 cycles of four minutes on and four off. These are manufacturer test procedures, not guaranteed life in every apparatus. Mounting position also remains subject to the instructions for the version used.