4689

Power Pentode — P8A

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Philips

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Known Equivalents & Substitutes

EL5/3754689P

Similar Tubes (Not Drop-In Compatible)

4689K

Different base type (Rimlock instead of P8A)

EL5

Same P8A base and pinout but lower max operating voltages (Va=250V, Vg2=250V vs 375V/275V for 4689) — not safe as drop-in in higher-voltage 4689 circuits

EL61

Successor type on different base — electrically similar but not pin-compatible

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Anode Voltage (max operating)375V

Screen Voltage (max)Screen Voltage (max operating)275V

Anode Dissipation (max)Anode Dissipation (max)18W

Screen Dissipation (max)Screen Dissipation (max, Vi=0)2W

Cathode Current (max)Cathode Current (max)

Notes

The 4689 is the Philips commercial designation for the EL5/375. The '/375' suffix indicates 375V max operating anode voltage, compared to 250V for the standard EL5. The 4689 also permits higher screen voltage (275V vs 250V). The max ratings (Wamax = 18W, Ikmax = 90 mA) are shared between both variants.
Philips strongly recommends automatic (cathode) grid bias for this tube. Published operating data for the 4689 relates to constant screen potential of 275V. If a potential divider feeds the screen, the screen voltage will fall as current increases with signal, reducing output power. Philips recommends stabilising the screen voltage with a voltage regulator tube (e.g. type 4687).
The gm and ra values (7 mA/V, 33 kΩ) are from the EL5 datasheet at Va = Vg2 = 250V. At the 4689's higher operating voltages (Va = 375V, Vg2 = 275V), gm may be somewhat higher due to increased space-charge effects.
The EL5 family was Philips' first 18W output pentode (1936), bridging the gap between the 9W generation (EL3N, EL2) and the later Rimlock/Noval types (EL41, EL84). The EL5 was succeeded by the EL61 (Rimlock base).
Heater current is 1.3–1.35A depending on source — too high for series-string heater circuits. Parallel heater supply only.

Pin Layout — P8A

1Anode

2Screen Grid (g2)

3Suppressor Grid (g3,

References