6EU8

The 6EU8 is a miniature triode–pentode intended chiefly for VHF frequency conversion in television receivers. The sheets describe the triode as oscillator and the pentode as mixer: two functions in one envelope, with separate cathodes. The triode has medium amplification factor and the pentode a sharp-cutoff characteristic. Heater requirements are 6.3 V, 0.45 A on AC or DC; the associated 5EU8 instead uses 4.7 V, 0.6 A.

A documented detail is the distinction between heater warm-up and attainment of a cathode-performance criterion. Average heater warm-up is 11 seconds under the prescribed test; RCA separately gives 35 seconds for the triode cathode. The latter is the time from a cold start to transconductance 6.5 mA/V at anode 100 V, grid 0 V and heater 5.5 V. The two times measure different quantities, not universal receiver waiting times.

RCA’s class-A1 table uses triode anode supply 150 V and cathode resistor 56 Ω: amplification factor 40, approximate anode resistance 5 kΩ, transconductance 8.5 mA/V and anode current 18 mA. The pentode uses anode and screen supplies 125 V, grid −1 V: anode current 12 mA, screen current 4 mA, transconductance 6.4 mA/V and approximate anode resistance 80 kΩ. Grid voltage for reducing anode current to 10 µA is −12 V triode and −9 V pentode; this differs from normal operating bias.

General Electric specifies design-maximum ratings of 330 V anode voltage for either section and 330 V screen supply. Maximum anode dissipation is 3 W triode and 3.1 W pentode; screen limit is 0.55 W, derated at higher voltages according to the curve. Maximum grid-circuit resistance is 0.1 MΩ for either section. Heater–cathode limit is 200 V total DC and peak in both polarities; when the heater is positive the DC component must not exceed 100 V. The RCA and Tung-Sol sheets examined instead head their limits design-center: the rating system must remain attached to its source.

Noval B9A base, JEDEC E9-1, bottom-view connection 9JF: 1 pentode anode, 2 triode grid, 3 triode anode, 4 and 5 heater, 6 triode cathode, 7 pentode control grid, 8 pentode cathode with suppressor and internal shield, 9 pentode screen grid. Any mounting position. RCA gives maximum overall length 2 3/16 inches, 55.5625 mm, maximum seated height 1 15/16 inches, 49.2125 mm, diameter 0.750–0.875 inch, 19.05–22.225 mm, and bulb height excluding tip 1 9/16 ±3/32 inches, 39.6875 ±2.38125 mm. Documentation: General Electric, 6EU8/5EU8 Triode-Pentode, ET-T1587, December 1959, seven pages; RCA, 6EU8 Medium-Mu Triode–Sharp-Cutoff Pentode, July 1961, two pages; Tung-Sol, 6EU8, tentative data February 1, 1960, three pages.