ECF804

The ECF804 is a combined triode-pentode for wideband amplifiers and instrumentation requiring high gain. Brimar’s August 1965 Issue 2 booklet gives both sections’ characteristics and six pages of curves. Available gain can be traded through negative feedback for broader, flatter response, but the valve type alone guarantees no particular bandwidth in an arbitrary circuit. Heater requirements are 6.3 V, 0.45 A.

Brimar’s triode characteristic point is plate 150 V, grid −1.5 V, plate current 13.5 mA, transconductance 7.2 mA/V, internal resistance 5.3 kΩ and amplification factor 38. The pentode at plate and screen 150 V, grid −2 V gives plate 7 mA, screen 2.2 mA, transconductance 11 mA/V and internal resistance 350 kΩ. The table gives approximately −3.5 V grid for plate current 100 µA. These are separate section characteristics, not a single mandatory combined circuit.

Triode capacitances are input 2.5 pF, output 1.5 pF, grid-plate 1.8 pF; the section designated pentode has 7 pF, 3.1 pF and below 0.02 pF respectively. Curves show current and transconductance versus bias, plus triode amplification factor and plate resistance. Photos of Brimar and Pinnacle specimens show inter-section screening; archived construction accounts also interpret the multigrid section as beam construction. The manufacturer’s designation remains triode-pentode: observations on specimens do not establish a different universal specification.

Brimar limits are plate 250 V and cathode current 20 mA per section. Maximum plate dissipation is triode 2 W, pentode 1.5 W; screen dissipation 0.5 W, maximum screen supply 250 V but actual screen voltage 175 V. Those last two quantities differ and do not permit applying 250 V directly to the screen. Both sections allow heater-cathode 150 V and maximum grid-cathode resistance 0.5 MΩ with fixed bias. Curves do not replace checking these limits in the chosen circuit.

Nine-pin Noval B9A connections: 1 triode plate, 2 pentode control grid, 3 pentode screen, 4–5 heater, 6 pentode plate, 7 pentode cathode/suppressor/screening, 8 triode cathode, 9 triode grid. Cathodes are separate. Both Brimar sheets give maximum diameter 22.2 mm and maximum body height 49 mm excluding pins; specimen and carton measurements are distinct. The summary marked Maintenance Type names CV5948 as equivalent, not proof of interchangeability with every secondary-source designation. Documentation: Brimar, ECF804, August 1965, Issue 2, seven pages, Thorn–AEI Radio Valves & Tubes Ltd.; Brimar, ECF804 Maintenance Type, page 205, data, connections and CV5948 reference.