← Reference

EL84

also 6BQ5 · 6BQ5 (US equivalent)

Philips/Mullard A.F. output pentode — the output valve of the Vox AC15 and of the wider Vox line. A noval bottle rated for 6 W from a single valve, it needs far less drive than the octal output tubes it displaced, and its short, sharp overdrive above roughly 300 V is much of the British combo voice. In the AC15 a pair runs cathode-biased from one shared 130 Ω resistor with no bias supply at all.

Basing (pinout)

Bottom view — the socket as you see it from the wiring side. Hover, tap, or focus a pin to name it. Read from the datasheet basing diagram (how to read these →).

1 2 3 4 5 6 7 8 9

Hover, tap, or focus a pin to name it.

  • High voltage (B+)
  • Control grid
  • Cathode
  • Heater / filament
  • Internal connection

Viewed from below (socket / wiring side) · noval 9-pin (B9A) · basing 9CV

⚡ Oxblood pins sit at B+ — hundreds of volts in service, lethal, and still charged after power-off.

Datasheets

Primary manufacturer data, via public tube-data archives. The model below is fitted to the tabulated "average characteristics" in these sheets; the datasheet files themselves are linked, never rehosted.

PublisherTypeSource
Philips / Mullard EL84 frank.pocnet.net ↗
RCA 6BQ5 frank.pocnet.net ↗

Circuit Codex model

A CC0 ngspice model in the Koren form, fitted here to the published anchor — no parameters copied from other model collections. Methodology →

Anchor
Va=250 V, Vg2=250 V, Vg1=-7.3 V → Ia=48 mA, Ig2=5.5 mA, gm=11300 µmho
Source
Philips/Mullard EL84 data sheet, January 1969 (A.F. Output Pentode), Class-A operating characteristics
Note
µ is the grid-No.1-to-grid-No.2 amplification factor (19), the tabulated amplification factor on the same Class-A data row as Ia/gm. As on the EL34 and unlike the KT66, the sheet tabulates Ig2 (5.5 mA) at the very same plate/gm operating point, so KG2 anchors there directly and no separate screen point is needed. EX=1.5 and KVB=30 (pentode) are project defaults per METHODOLOGY.md. Known limitation: this is a single-anchor fit at 250 V, used in the AC15 at a 315 V rail — the extrapolation is the usual v0 caveat, and it lands the AC15 output stage at a physically sensible 11 V of cathode bias.
File
models/el84.inc ↗

See these parameters drawn: the load line explorer plots the EL84's plate-curve family from this model and solves an operating point on it.

Maximum ratings

Limiting values under the design-centre rating system. Two anode figures are printed: 550 V standing with no current drawn, and 300 V in operation. The AC15 sits right on that second number — the factory drawing annotates +310 V on the EL84 anodes off a +315 V rail — and with the pair sharing one 130 Ω cathode resistor the simulated idle point lands within a couple of percent of the 12 W anode ceiling. That is the whole character of the circuit: a cathode-biased pair run essentially flat out, with no bias supply to back them off.

Anode voltage, no current
550 V
Anode voltage
300 V
Anode dissipation
12 W
Grid No.2 voltage, no current
550 V
Grid No.2 voltage
300 V
Grid No.2 dissipation
2 W · 4 W peak
Negative grid-No.1 voltage
100 V
Cathode current
65 mA
Grid-No.1 resistor
1 MΩ automatic bias · 0.3 MΩ fixed bias
Cathode-to-heater voltage
100 V
Rating system
Design centre — carries an allowance for manufacturing spread
Source
Philips/Mullard EL84 data sheet, January 1969 — limiting values (design-centre rating system) ↗