8.5V heater variant of 6BQ5/EL84 — same Noval base and pin layout but different heater voltage (8.5V vs 6.3V). Not interchangeable without heater circuit modification.
UEL84
100V series heater string version of EL84 — same Noval base and pin layout but 100V/45mA heater for AC/DC receivers. Not interchangeable.
Screen dissipation is 2 W max normally, but 4 W is permitted under maximum-signal conditions (music/speech short-term).
Grid 1 circuit resistance: 0.3 MΩ max for fixed-bias operation, 1 MΩ max for cathode-bias operation.
Pin 1 is sometimes used internally as a second g1 connection for mechanical reasons only — it must not be used externally.
Pins 1, 6, and 8 are internal connections and should not be wired.
7189 and 7189A are higher-rated variants (not direct equivalents); 6GK6 is functionally similar but has a different pinout.
Triode-strapped μ, gm, and ra sourced from Tom Schlangen's 'Pentodes Strapped as Triodes' (2009) measured data table; SE triode operating point (Va, Ia, Rk, rl, Pout) from TDSL. The RCA 6BQ5 datasheet does not include triode-connection data.
Pin Layout — Noval
1Internal Connection
2Control Grid (g1)
3Cathode (g3 internally connected)
Socket-Compatible Tubes ⚠ Not electrically compatible