UCC85

The UCC85 is a double triode for RF amplification and self-oscillating mixing in receivers. Philips explicitly presents FM/AM service; Tesla describes electrically equal systems with high transconductance, separate cathodes and an internal inter-section shield, suited to FM radio and television receivers. One section can serve RF amplification and the other conversion, under specified service conditions. The indirectly heated heater requires 100 mA at nominal 26 V for series AC or DC supply; matching base appearance does not justify substituting another tube’s heater rating.

Editions differ in characteristic values. Philips 1954–1955 and Tesla 1959 give, at plate 170 V and grid −1.5 V, plate current 10 mA, transconductance 6.2 mA/V and amplification factor 50. Philips 1969 instead gives grid −1.75 V at plate 170 V, still 10 mA, transconductance 6.7 mA/V and factor 48. These are separate tables, not values to average. At the 100 V point with weak negative bias, Philips warns that grid current may occur; if unacceptable it specifies −1.5 V bias. This note completes the meaning of the numerical row.

A Philips 1969 RF example uses supply 170 V, plate resistor 1.5 kΩ and cathode resistor 150 Ω: resulting plate voltage 155 V, current 9.8 mA, transconductance 6.7 mA/V and equivalent noise resistance 0.55 kΩ. A self-oscillating mixer example at supply 170 V, plate resistor 4.7 kΩ, grid resistor 1 MΩ and oscillation 2.8 V RMS gives plate current 5.5 mA and conversion transconductance 2.8 mA/V. Supply, actual plate voltage and conversion transconductance are distinct quantities.

Earlier notes add circuit details. Philips relates prevention of squegging to the feedback provided in the mixer with 1 MΩ grid resistor. Tesla specifies RF bypassing the external plate-circuit resistor with 1 kpF, or 1000 pF, and avoiding RF voltage between heater and cathode to limit microphony in oscillator use. These are source application instructions, not guaranteed performance without that circuit. Capacitances also depend on maker and conditions: Philips gives plate-grid 1.5 pF, Tesla 1.85 pF; Philips’s measurement shield diameter 22.5 mm is not tube diameter.

Limits include operating plate voltage 250 V, no-current voltage 550 V, cathode current 15 mA per section and plate dissipation 2.5 W per section, but 4.5 W for both together. Adding individual maxima does not permit 5 W total. Philips gives cathode-heater 90 V; Tesla distinguishes 200 V with cathode positive and 90 V with cathode negative relative to heater. Philips 1954–1955 and Tesla limit external resistance between them to 20 kΩ. Maximum grid resistance is 1 MΩ. Source differences remain explicit.

The noval base assigns pins 1, 2, 3 to plate, grid, cathode of one section; 6, 7, 8 to the other; 4 and 5 heater, 9 internal shield. Philips 1954–1955 gives maximum diameter 22 mm, body excluding pins 49.2 mm and overall 55.6 mm; Philips 1969 maximum diameter is 22.2 mm. Tesla dimensions overall 56.3 mm and body 49.2 mm are not marked maximum; diameter maximum 22.2 mm, mass about 15 g. Documentation: Philips, UCC85, November 11, 1954 sheets, partly tentative, and September 9, 1955; Philips, UCC85, January and December 1969; Tesla, UCC85, November 10, 1959, four pages. Document dates do not date photographed specimens.