E88C = 8255 Triode

E88C / 8255 special-quality single triode for audio DIY and test equipment

The E88C, also designated 8255, is an indirectly heated special-quality single triode on a 9-pin Noval B9A base. Its transconductance of 13.5 mA/V, amplification factor of 70 and plate resistance of 5.2 kOhm make it an interesting building block for purpose-designed line, buffer and driver stages.

The valve was originally developed for grounded-grid aerial amplifiers in UHF Bands IV and V. Philips documents gold-plated pins, shock and vibration resistance, and a 10,000-hour life test on production samples. The E88C must not be confused with the E88CC or 6922 double triode.

Suitable applications

• purpose-designed audio line, buffer and driver stages
• grounded-grid stages driven from a low source impedance
• laboratory, test and professional RF equipment
• repair and restoration of Band IV and V UHF front ends

Technical data

Valve type

Special-quality single triode, indirectly heated

Base

9-pin Noval B9A with gold-plated pins

Heater

6.3 V / 155 mA, AC or DC

Typical operating point

Va 160 V, Vg −1.25 V, Ia 12.5 mA

Transconductance

13.5 mA/V

Amplification factor

70

Plate resistance

5.2 kOhm

Maximum plate dissipation

2.6 W

Maximum plate voltage

200 V in operation; 400 V under cold conditions

Maximum cathode current

16.5 mA

Heater-to-cathode voltage

maximum +125 V or −60 V, referenced to the cathode

Dimensions

maximum diameter 22 mm and overall height 55.6 mm

Pin connections

Pins 1, 3, 6, 7 and 9

Control grid

Pin 2

Cathode

Pins 4 and 5

Heater

Pin 8

Plate

Application and circuit-design notes

All five g connections belong to the same control grid. Because this is a high-transconductance valve, keep signal paths short, use solid grounding and supply decoupling, and fit a grid stopper at the socket when required for stability. E88CC/6922 has a different internal system and pinout. EC88/6DL4 is technically related but does not automatically provide the same special-quality specification, while PC88 also requires a different heater supply. Hazardous voltages may be present, so commissioning should be carried out by qualified personnel.

Questions about selection and use

Is the E88C/8255 triode suitable for an audio line or driver stage?

Yes, its 13.5 mA/V transconductance and 5.2 kOhm plate resistance provide an interesting basis for purpose-designed line, buffer or driver stages. Bias point, load, stabilization and layout must be engineered for this single triode.

Can the E88C/8255 triode be used in test and RF equipment?

Yes, the E88C/8255 was originally designed for grounded-grid aerial amplifiers in UHF Bands IV and V. It is therefore suitable for appropriate repairs, laboratory setups and newly engineered RF circuits.

Is 8255 a valid equivalent designation for the E88C triode?

Yes, Philips lists 8255 and E88C in the same data sheet. The similarly named E88CC or 6922 is a different double triode with another pinout and is not a direct substitute.