PCF801 Triode/Pentode tube Radio / TV Röhre

PCF801 triode and variable-mu pentode for custom tube-audio DIY

The PCF801 combines a high-transconductance triode and a variable-mu RF pentode in one compact Noval B9A envelope. Both sections share a common cathode. Originally designed as a VHF frequency changer, it is now of particular interest for budget-conscious valve experiments, purpose-designed small-signal circuits and technical learning projects.

For tube-audio DIY, the PCF801 may be explored in custom gain, driver or oscillator stages. It is not a conventional audio output valve and is not a plug-in alternative to an ECC83, ECC82 or another standard preamp valve. Hi-fi, studio and guitar-amplifier applications therefore require a circuit designed specifically around its heater, shared cathode and operating characteristics.

Suitable applications

• Purpose-designed tube-audio small-signal and driver stages
• Valve oscillators, signal generators and laboratory circuits
• Experimental hi-fi, studio and guitar-amplifier DIY projects
• Repair of equipment specifically designed for the PCF801
• Legacy VHF mixer, oscillator and intermediate-frequency stages

Technical specifications

Valve construction

High-transconductance triode and variable-mu RF pentode with a shared cathode

Base

Noval B9A, 9-pin

Heater

8.5 V at 300 mA, indirectly heated, suitable for AC or DC series-heater operation

Dimensions

Maximum diameter 22.2 mm, maximum bulb height 43.6 mm, maximum overall height 50.0 mm

Triode – typical operating point

Va 100 V, Vg −3 V, Ia 15 mA, transconductance 9 mA/V, amplification factor µ 20

Pentode – typical operating point

Va 170 V, Vg2 120 V, Vg1 −1.4 V, Ia 10 mA, Ig2 3 mA, transconductance 11 mA/V

Pentode – gain data

Amplification factor µg2g1 55, internal resistance at least 350 kΩ

Triode limits

Maximum anode voltage 125 V, maximum anode dissipation 1.5 W

Pentode limits

Maximum anode voltage 250 V, maximum anode dissipation 2.0 W

Cross-reference

8GJ7 is frequently cross-referenced to the PCF801, but published differences mean that it should not be treated as an unchecked one-for-one substitute

B9A base connections – bottom view

Pins 1 and 3

Common cathode for the triode and pentode, pentode suppressor grid g3 and internal shield

Pin 2

Pentode control grid g1

Pins 4 and 5

Heater

Pin 6

Pentode anode

Pin 7

Pentode screen grid g2

Pin 8

Triode anode

Pin 9

Triode control grid

Notes for circuit designers

The common cathode prevents straightforward independent cathode-bias arrangements for the two sections and must be considered from the beginning of the design. The operating points shown in the data sheet are reference conditions rather than a universal audio construction recipe.

Safety notice: The 8.5 V heater requirement is not the anode-supply voltage. Valve circuits may contain lethal voltages and should only be assembled, tested and commissioned with suitable knowledge and safety precautions.

BTB has specialised in electronic valves and components for amplifier construction, repair, workshop use and professional valve technology since 1946.

Questions about selection and DIY use

Can the PCF801 be used in a hi-fi preamp or guitar amplifier?

Yes, but only in a small-signal or driver circuit calculated specifically for the PCF801. It was not developed as a standard audio preamp valve, its two sections share a cathode and it is not a plug-in replacement for an ECC83 or ECC82. Existing amplifiers should use it only when the original circuit specifies the PCF801 or when the circuit has been properly redesigned.

What supplies does the PCF801 require in a tube-audio DIY project?

The heater requires 8.5 V at 300 mA. Typical data-sheet conditions are 100 V anode voltage at 15 mA for the triode and 170 V anode voltage, 120 V screen voltage and 10 mA anode current for the pentode. These figures are design references and must not be copied into every audio circuit without recalculating the operating point.

Are the 8GJ7, PCF803 or ECC83 direct replacements for the PCF801?

No. The 8GJ7 is often listed as a cross-reference, but published RCA data differs in heater voltage and pentode classification. The PCF803 uses a different pin arrangement, while the ECC83 and ECC82 are twin triodes with different heater, pinout and operating requirements. The valve data, base connections and equipment circuit must be checked before substitution.