Single Vintage TESLA ECH81 Vacuum Tube - Made in Czechoslovakia - October 1967 NOS Triode-Heptode (Multi-Quantity Available)

Available for purchase is a premium vintage ECH81 triode-heptode vacuum tube manufactured by TESLA in Czechoslovakia. Multiple pieces are available from the identical factory-matching production lot. Every tube features original yellow factory stencils, a pristine clear glass envelope, and a grey internal shield stamped with batch "16" and date code "KR".According to the historical TESLA coding system, the "KR" stamp verifies that these units were produced in October 1967. These are pristine New Old Stock (NOS) pieces with perfectly straight, clean pins and zero signs of socket wear or oxidation.The TESLA ECH81 (fully equivalent to 6AJ8, 6И1П, and X79) is a miniature 9-pin multi-unit tube combining an independent triode and a heptode section within a single envelope. It is primarily utilized as an oscillator, frequency changer, and mixer stage in classic high-fidelity European AM/FM tube receivers. Using this authentic 1967 factory stock ensures optimal conversion gain, excellent frequency stability, and reliable long-life operation across multi-band tuning sections.Technical Specifications and Parameters:

• Brand: TESLA (Czechoslovakia)
• Tube Type: ECH81 / 6AJ8 (Triode-Heptode Frequency Changer / Mixer)
• Production Date: October 1967 (Factory code KR)
• Base Type: Miniature 9-Pin (Noval / B9A / JETEC E9-1)
• Filament/Heater Voltage: 6.3V AC/DC
• Heater Current: Nominal 300 mA
• Heptode Section Anode Voltage: 250V DC
• Heptode Section Screen Grid Voltage (G2+G4): 100V DC
• Triode Section Anode Voltage: 100V DC
• Heptode Conversion Transconductance: 0.75 mA/V (750 µmhos)
• Triode Section Transconductance: 3.7 mA/V (3,700 µmhos)

Pinout Connections (Bottom View - Noval B9A):

• Pin 1: Triode Anode
• Pin 2: Heptode Grid 1 (Control Grid)
• Pin 3: Heptode Cathode, Grid 3, and Internal Shield
• Pin 4: Heater
• Pin 5: Heater
• Pin 6: Heptode Anode
• Pin 7: Heptode Grids 2 and 4 (Screen Grids)
• Pin 8: Triode Grid and Heptode Grid 3 (Common Connection)
• Pin 9: Heptode Grid 3 (Suppressor Grid)

Shipping:
The tube will be wrapped meticulously in multi-layer heavy-duty bubble wrap and packed securely inside a thick cardboard shipping box to ensure 100% safe international transit. Worldwide shipping with a tracking number provided immediately upon dispatch. Please feel free to reach out with any technical or compatibility questions.