EC56

The EC56 is a Philips disc-seal triode for low-level amplification, especially broadband grounded-grid microwave amplifiers. The EC56/EC57 application chapter places both types in oscillators and amplifiers for microwave relay links up to about 4,000 MHz. Their construction suits coaxial lines and waveguides: the grid disc separates plate and cathode circuits, and its thread provides both mounting and RF contact. Simply inserting the base in an ordinary socket does not reproduce the documented microwave mounting.

The handbook describes planar construction with an L-type cathode and about 40 µm spacing between grid and hot cathode. EC56 and EC57 are mechanically identical but electrically different; EC56 also drives EC57 in a two-stage amplifier. EC56 is indirectly heated, AC or DC, parallel supply 6.3 V, 650 mA. The 12 December 1958 sheet permits heater-voltage variation no greater than ±2% and specifies, at plate 180 V and 30 mA, nominal bias −2.8 V, transconductance 17 mA/V and amplification factor 43.

RF conditions must retain their document revision. The updated sheet gives, at 4,000 MHz, plate supply 200 V, grid supply +20 V and plate current 30 mA, with adjustable cathode resistance up to 1 kΩ to set current. Positive grid supply refers to the cathode-resistor circuit, not positive grid-to-cathode bias overriding the 0 V limit. Gain is 12 dB, minimum 10 dB, at 1 mW output; at 6 dB gain output is 0.5 W, minimum 0.35 W. The 50 MHz bandwidth is between the flattened response’s 0.1 dB points, not half-power points.

The handbook instead labels its data tentative: at 180 V and 30 mA, bias −3.5 V, transconductance 16 mA/V and factor 35. Its 4 GHz examples use supplies 220 V and +40 V, half-power bandwidths 100 or 50 MHz, gains 13 and 17 dB at 1 mW and outputs 0.6 and 1.2 W at 8 dB gain. These results must not be combined with or substituted for later sheet conditions. Capacitances also differ: the 1958 sheet gives plate-grid 1.6 pF, plate-cathode 0.04 pF and grid-cathode 3.3 pF at zero cathode current; the tentative handbook gave 1.6, 0.02 and 2.2 pF.

Sheet absolute maximums include operating plate 300 V, cold plate 500 V, plate dissipation 10 W, cathode current 35 mA and grid current 10 mA. Negative grid-bias magnitude is limited to 50 V, positive bias to 0 V, cathode-heater voltage to 50 V and RF input power at 4 GHz, grounded grid, to 0.5 W. Maximum anode-seal temperature is 150 °C in the sheet versus 200 °C in the tentative handbook; grid and cathode seals are limited to 75 °C. Philips notes that gentle airflow may be required and warns against shocks, especially perpendicular to the tube axis in transportable equipment.

The modified octal base has heater pins 2 and 7, cathode 3 and 8, internal connections 1 and 5 that must not be treated as unused terminals; plate and grid use dedicated external contacts. The datasheet drawing gives maximum overall length 60 mm, height above base seat 45.5 mm and transverse outline 32.8 mm. The grid disc uses a 32-threads-per-inch, 60° thread; support shape and contact tolerances are part of the RF mounting. Documentation: Philips EC56 sheets revised 1957 and 1958, curves 1956; Philips S.H.F. Disc-Seal Triodes EC56 and EC57, application chapter pages 33–40, tentative data.