C3C

The C3c is a variable-control pentode, presented by RFT as “Regel-Pentode” and listed in our sources among telephone tubes for long-distance links. The available sheet’s key feature is a comparison of two grid biases, showing changes in current and transconductance without assigning one generic behaviour to all pentodes. Specified heating is 4 V, 1.1 A. The VEB Röhrenwerk Anna Seghers sheet, Neuhaus am Rennweg, is the February 1956 edition: a document date, not an assumed introduction date.

With plate 220 V and screen 100 V, the table gives two conditions. At g1 −2 V: plate current 10 mA, screen current 3.5 mA, transconductance 2.5 mA/V; at g1 −18 V: respectively 1.5 mA, 0.5 mA and 0.1 mA/V. More negative bias markedly reduces response but does not eliminate current, so −18 V is not presented as cutoff. Internal resistance 650 kΩ is printed for the first point; the second column has no value to fill in by analogy.

RFT maxima are operating plate voltage 250 V, plate dissipation 2 W, screen voltage 100 V and screen dissipation 1 W. Cold plate and screen voltages are instead 400 V, distinct from service limits. Maximum g1 leak resistance 300 kΩ. Grid-plate capacitance is written 8 mpF, meaning 0.008 pF, not 8 pF. Light-type figures not marked as limits are stated to be approximate; the general-conditions reference also emphasizes heater tolerance ±5%.

Printed base code WN–P7/1–3. The functional drawing shows g1 at the top contact, with plate, g2, cathode joined to g3, heater and contact m at the base; it introduces no pin numbers. RFT maximum dimensions are diameter 53 mm, overall length 148 mm and pin projection 15 mm, approximate mass 80 g. Available photos show an RWN Neuhaus specimen with RFT box and one marked Siemens Austria, both C3c: external variants, without automatically assigning RFT dimensions to every specimen. Documentation: RFT, C3c, VEB Röhrenwerk Anna Seghers, two-page technical sheet, February 1956.