DL963

The RFT DL963 is a pentode explicitly intended for high- or low-frequency amplification. VEB Röhrenwerk Anna Seghers specifies direct heating with a centre-tapped filament: 1.2 V, 200 mA with halves in parallel, or 2.4 V, 100 mA in series. The parallel arrangement notes centre tap fM at the negative pole. Old imported 1.4/2.8 V figures do not replace these primary data.

The stated operating point has plate 150 V, screen 67.5 V and control grid −7.5 V. Figures are plate current 10 mA, screen current 2.6 mA, transconductance 2.2 mA/V, internal resistance 90 kΩ and external load 12 kΩ. With 4.5 V RMS grid drive and 10% distortion, output is 630 mW. These conditions jointly describe low-frequency performance; a title also allowing HF use does not establish maximum frequency or guaranteed RF output.

Maximum values are plate voltage 150 V, plate dissipation 1.5 W, screen voltage 90 V, screen dissipation 0.35 W, cathode current 18 mA and control-grid leak resistance 0.5 MΩ. Maximum screen voltage is thus distinct from the 67.5 V operating point. Capacitances are input 6 pF, output 2.5 pF, control grid-cathode 1.2 pF and control grid-plate 0.3 pF. Figures printed in light type and not marked as limits are approximate according to the manufacturer.

The base is a seven-contact miniature, classified B7G by archive information. The unnumbered functional drawing shows two plate contacts, g1, g2, filament ends and centre tap fM joined to g3. Maximum dimensions: bulb diameter 19 mm, body height excluding pins 47.6 mm and pin projection 7 mm; no sum is offered as a stated overall length. Weight approximately 7 g. Manufacturer, document and dimensional qualification remain attached to each technical record.

For screening and mounting the sheet cites nominal size 38 under DIN 41537 and accessory supplier Gebr. Kleimann, Berlin-Lichtenberg. The tube maker named in the document remains Röhrenwerk Anna Seghers, not the screening supplier. General operating conditions are referenced but not reproduced, so absent instructions are not invented. Documentation: RFT, VEB Röhrenwerk Anna Seghers, DL963, Pentode für HF- oder NF-Verstärkung, December 1956 edition, two pages. This dates the source, not automatically the type’s introduction.