What is a ECLL800 substitute or equivalent?

Direct equivalents to the ECLL800 include 6KH8. These share the same pinout and operating envelope, so they can usually be swapped without circuit changes — though batch-to-batch variations between manufacturers (NOS vs current production) may shift the sonic character noticeably.

What are the key specifications of the ECLL800?

Amplification factor μ ≈ 17, transconductance gm ≈ 6 mA/V, plate resistance rp ≈ 100.0 kΩ, max plate voltage 300 V, max plate dissipation 6 W, heater 6.3 V / 0.6 A.

Is the ECLL800 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the ECLL800 as Rare availability. NOS (new-old-stock) examples from RCA, Mullard, Tung-Sol, GE, Sylvania and Telefunken trade among collectors; modern production where it exists comes mostly from JJ Electronic, Electro-Harmonix, Tung-Sol (New Sensor), Genalex, and a handful of small-batch makers.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

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ECLL800 ECLL800 / 6KH8 Pentode Vacuum Tube

Q: What is the ECLL800 vacuum tube?

The ECLL800 (ECLL800 / 6KH8) is a pentode vacuum tube designed for power (pp) — unidrive applications. Late-1963 Lorenz 'unidrive' triple: two beam-pentode output sections + a low-mu phase-inverter triode in a single B9A Noval envelope. Designed to give a full push-pull output stage from a single drive signal, delivering ~8.5 W in Class AB and ~9.2 W in Class B with 5 % THD into 10–11 kΩ plate-to-plate. The triode is not a gain stage but a unity-gain phase splitter (load = 150 kΩ) deliberately curved to compensate the pentodes' non-linearity. Short production run, used in compact European stereo amplifiers of the mid-1960s..

Q: What does the ECLL800 sound like?

Late-1963 Lorenz 'unidrive' triple: two beam-pentode output sections + a low-mu phase-inverter triode in a single B9A Noval envelope. Designed to give a full push-pull output stage from a single drive signal, delivering ~8.5 W in Class AB and ~9.2 W in Class B with 5 % THD into 10–11 kΩ plate-to-plate. The triode is not a gain stage but a unity-gain phase splitter (load = 150 kΩ) deliberately curved to compensate the pentodes' non-linearity. Short production run, used in compact European stereo amplifiers of the mid-1960s.. Sonic character also depends heavily on the circuit operating point, the surrounding tubes in the stage, and the output transformer when present — use the interactive loadline calculator on this page to explore the trade-offs.

Dual pentode6.3V / 0.6A9-pin Noval

SourceLorenz ECLL800 preliminary datasheet (30 March 1963) + Practical Wireless March 1964Reviewed2026-05-29StatusDataModelCalcModelmanual entryPDF

Small-signal pentode for low-noise voltage amplification

Datasheet ↗

100.0kΩ

6.0mA/V

8.2pF

0.2pF

5.00pF

GAIN17%

POWER15%

DRIVE0%

LINEARITY92%

SPECIFICATIONS

Heater6.3 V · 0.6 A

Max Plate Voltage300 V

Pa max6 W

Gain Factor17

gm6 mA/V

rp100.0 kΩ

Inter-electrode capacitances

Cgk8.2 pF

Cgp0.2 pF

Cpk5 pF

Pinout9-pin Noval

Era1963

RarityRare

HEATER6.3V / 0.6A

MAX PLATE300V / 6W

BASEnoval

SECTIONS3 (dual)

Vhk max200V

Manufacturer datasheets (PDF downloads)

Lorenz (Stuttgart)

30 March 1963 · 4 pp · DE · EN

Preliminary datasheet: pinout, heater, static measurement points (per power section and per triode), Class B and Class AB push-pull operating tables, limiting values, inter-electrode capacitances.

Practical Wireless (M. L. Michaels)

March 1964 · 8 pp · EN

First English-language application article describing the ECLL800 as a 'Unidrive push-pull output valve'. Defines the unidrive principle, explains the unity-gain phase-inverter triode (150 kΩ load), introduces the curvature-compensation concept, and gives the complete 7-20 Stereo Amplifier (2× ECLL800 + EF86 + 3× ECC83 + EZ81, 11 kΩ aa OPT, 250-0-250 V / 150 mA PSU).

French technical article (after Radio Electronics Nov 1963)

circa 1963-1964 · 6 pp · FR

French-language synthesis: explains the 'triple tube — triode + double power pentode' architecture, gives the optimised design (24 dB feedback, ~10 W out at 1 kHz, 1.5 V RMS input, IMD < 1.5 % 60 Hz/7 kHz 4:1) inspired by Radio Electronics Nov 1963. Notes that an EL84 / 6V6 push-pull OPT is acceptable if Raa ≈ 11 kΩ.

Radiomuseum.org

accessed 2026-05-22 · 1 pp · EN · DE

Cross-reference catalog page: confirms Lorenz origin, 6KH8 designation, era 1963, B9A Noval, dimensions (Ø 22.2 mm, height 71.4 mm, mass 17 g).

Source datasheets

1 manufacturer datasheets cross-checked for ECLL800 / 6KH8

1 verified

EXECUTIVE SUMMARY

The ECLL800 is a indirectly-heated pentode from Lorenz·ITT Lorenz, introduced around 1963. It provides a gain factor (μ) of 17 with 100.0kΩ plate resistance. Commonly used in power (pp) — unidrive applications. Late-1963 Lorenz 'unidrive' triple: two beam-pentode output sections + a low-mu phase-inverter triode in a single B9A Noval envelope. Designed to give a full push-pull output stage from a single drive signal, delivering ~8.5 W in Class AB and ~9.2 W in Class B with 5 % THD into 10–11 kΩ plate-to-plate. The triode is not a gain stage but a unity-gain phase splitter (load = 150 kΩ) deliberately curved to compensate the pentodes' non-linearity. Short production run, used in compact European stereo amplifiers of the mid-1960s.

HISTORY

Introduced1963ManufacturerLorenz·ITT Lorenz

Late Production