← Reference

6SL7GT

also 6SL7 · 6SL7-GT · 7F7 (loctal base) · 12SL7GT (12.6 V heater) · 14F7 (loctal, 12.6 V heater)

High-mu (µ=70) twin triode on an octal base — the octal counterpart of the 9-pin 12AX7, and the preamp and phase-inverter bottle of the Ampeg circuits. Tung-Sol states the design intent outright: the tube "combines two independent high-mu triodes in one envelope" and "is designed primarily for phase inverter service." The two units are wired symmetrically around the base — grid, plate and cathode of unit No.2 on pins 1 to 3, the same three for unit No.1 on pins 4 to 6 — which is what lets a long-tailed pair share one socket with no crossed leads. A watt of plate dissipation per unit puts it firmly in small-signal service.

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

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

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

Viewed from below (socket / wiring side) · octal · basing 8BD

⚡ 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
RCA 6SL7-GT frank.pocnet.net ↗
Tung-Sol 6SL7GT (plate 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, Vg=-2 V → Ia=2.3 mA, gm=1600 µmho, µ=70
Source
RCA 6SL7-GT data sheet, November 5, 1954 — Amplifier Class A1, characteristics, values for each unit
Note
Single-anchor fit at the one operating point either publisher tabulates: KP and KG1 are solved so the model reproduces plate current and transconductance exactly there, the same treatment the 12AY7, 6AT6 and 12AT7 models get. µ=70 is the printed amplification factor, not a substitution — this is a plain triode, so the printed figure is the quantity the model wants, and the sheet's own gm·rp confirms it: 1600 µmho × 44 kΩ = 70.4. EX=1.5 and KVB=300 V² are the project triode defaults per METHODOLOGY.md. A fitted KVB would need a sheet tabulating plate current at two plate voltages at the same grid voltage, as the 6SJ7's does; neither publisher gives one here. RCA prints a single 250 V characteristics column, and Tung-Sol's second table is a resistance-coupled amplifier design chart, which tabulates plate supply voltage through a load resistor rather than a static characteristic.
File
models/6sl7gt.inc ↗

See these parameters drawn: the load line explorer plots the 6SL7GT's plate-curve family from this model and solves an operating point on it.

Maximum ratings

Design-centre values, each unit. One watt of plate dissipation and a 300 V plate ceiling are the whole envelope — this is a small-signal tube, and the grid must never be driven positive. Both publishers print the same block.

Plate voltage
300 V
Grid voltage, positive bias value
0 V
Plate dissipation
1 W
Peak heater-cathode voltage, heater negative with respect to cathode
90 V
Peak heater-cathode voltage, heater positive with respect to cathode
90 V
Rating system
Design centre — carries an allowance for manufacturing spread
Source
RCA 6SL7-GT data sheet, November 5, 1954 — Amplifier Class A1, maximum ratings (design-centre values), values for each unit; identical on the Tung-Sol 6SL7GT sheet, March 1, 1959 (ratings interpreted according to the design centre system) ↗