C-EM2

The archive designation C-EM2 corresponds to C/EM2 printed on Philips Miniwatt documents: an electronic tuning indicator with fluorescent screen and a triode in one bulb. Its conical screen is viewed from above, showing two fan-shaped luminous sectors. Tuning changes their width and brightness. Philips compares it with EM1: C/EM2 has two deflecting elements instead of four, plus an additional grid in the indicator system.

Operation offers several options. The triode can amplify AGC DC voltage; its changing anode voltage alters deflection by supports extending into the fluorescent system. Alternatively, the indicator grid can control light intensity down to disappearance while also changing sector angle. The triode then remains available for other functions, including interference suppression or AGC-voltage amplification in Philips’ examples. Both controls can also be combined.

The text describes a useful weak-signal effect: off tune, sectors may be narrow and dim; approaching the carrier increases brightness and area, then after light saturation they may widen to about 150° on a strong carrier. A cathode shield prevents cathode light interfering with observation. Table angles refer to one luminous sector measured at the screen edge, not an arbitrarily combined angle of both sectors.

Indirect heating 6.3 V, 0.2 A, AC or DC, series or parallel. Triode points: anode 200 V/grid −2.5 V or anode 250 V/grid −3.5 V; both give anode current 3 mA, transconductance 2 mA/V, amplification factor 50, internal resistance 25 kΩ. In the 4 July 1940 sheet, with screen and triode anode both 200 V, indicator-grid −4.5, 0 and +3 V yield 5°, 150° and 160°. At 250 V for both, −6, 0 and +3 V give those angles.

A second 1940 comparison fixes indicator grid at 0 V and varies triode anode: screen 200 V, anode 0 to 200 V gives sector 90° to 150°; screen 250 V, anode 0 to 250 V gives 95° to 150°. Numerous curves mark decreasing-intensity regions with broken lines. The Dutch page 38 arranges the extreme negative grid values differently between columns from the 1940 sheet; the numerical examples above follow the latter without mixing editions.

1940 limits: triode anode 300 V, triode dissipation 1.5 W, fluorescent screen maximum 250 V/minimum 150 V, screen current 1 mA, cathode current 12 mA; Va0 and Vs0 are each 550 V. Maximum grid-cathode resistance of each system 2.5 MΩ, heater-cathode resistance 20 kΩ. Maximum heater-cathode difference is 100 V DC or AC RMS in the 1940 and German copies; English and Dutch give 125 V. English/German application text additionally requires at least 200 V on screen, while the limit table gives minimum 150 V: application recommendation and limit table remain distinct.

The 1940 drawing gives maximum diameter 31 mm, maximum overall height 75 mm, base dimension 30 mm. Side contacts: two heaters f, cathode k, triode grid g, indicator grid g′, triode anode/deflectors A/D, luminous screen l; the remaining contact has no assigned function in the functional drawing. Viewing direction is not explicit there. The retained photo shows C/EM2 marking and fluorescent assembly above the triode. Documentation: Philips Miniwatt C/EM2, German and English descriptions/curves, five pages each, printed pages 139–143; Philips C/EM2 Kathodestraalindicator, page 38; Philips Miniwatt C/EM2, tables/curves, four pages, 4 July 1940.