E180F (=6688, =CV6189, =6J9) steile Pentode tube made in EU

E180F / 6688 high-gm SQ pentode for phono, preamp and driver DIY

The E180F is a special-quality high-transconductance pentode originally developed for wideband amplifiers in professional equipment. BTB lists this version as a European-made Tesla valve specified for telecommunications service. The same valve system is also known under designations including 6688, CV6189 and CV3998.

With approximately 16 mA/V transconductance in pentode operation, the E180F can provide substantial voltage gain from a single stage. When triode strapped, the Philips data gives 21 mA/V transconductance, an amplification factor of 50 and a plate resistance of approximately 2.4 kΩ. These characteristics make it an appealing sleeper valve for value-focused phono, line-level, driver and high-end audio projects.

The E180F belongs in the same design conversation as valves such as the D3a, E280F, E810F, C3m and C3g, but it is not a plug-in substitute for them. A new circuit must be designed around its own heater requirement, pin connections, operating current and maximum ratings.

Useful tube-audio applications

• Custom phono stages with an input and RIAA network designed for the valve
• High-gain input stages for line-level and studio preamplifiers
• Voltage-amplifier and driver stages for larger audio output valves
• Triode-strapped gain stages and high-impedance preamplifier outputs
• Balanced, differential and two-channel circuits using selected valves
• Service of professional equipment originally designed for the E180F or 6688

Technical specifications

Valve type

High-transconductance special-quality wideband pentode with indirect heating

Offered production version

European Tesla production described by BTB as originally specified for DDR telecommunications service

Equivalent and search designations

6688, CV6189 and CV3998; 6J9 or 6Ж9П is also used as a comparison designation, although the individual manufacturer's data should be checked

Base

Noval B9A, 9-pin

Heater

6.3 V at 300 mA, indirectly heated, suitable for AC or DC operation

Heater-voltage guidance

For extended service life, Philips recommends keeping heater-voltage variation below ±5%

Dimensions

Maximum bulb diameter 22 mm, maximum bulb height 38 mm and maximum overall height 45 mm

Pentode reference condition

Va 180 V, Vg2 150 V, Rk 100 Ω, Ia 11.5 mA and Ig2 2.9 mA

Pentode transconductance

15.9 mA/V at the 180 V reference condition; another Philips reference condition specifies a nominal 16.5 mA/V

Pentode gain data

Screen-to-control-grid amplification factor µ_g2/g1 50 and approximately 90 kΩ internal resistance at the nominal reference condition

Equivalent RF noise resistance

Typically approximately 460 Ω as a pentode and 225 Ω when triode strapped

Triode-strapped characteristics

Ia 16.5 mA, transconductance 21 mA/V, amplification factor µ 50 and approximately 2.4 kΩ plate resistance in the Philips reference condition

Capacitances

Input capacitance 7.5 ±0.9 pF and control-grid-to-anode capacitance below 0.03 pF

Maximum operating anode voltage

210 V

Maximum anode dissipation

3 W

Screen-grid limits

Maximum operating Vg2 175 V and maximum screen-grid dissipation 0.9 W

Maximum cathode current

25 mA

Maximum heater-to-cathode voltage

60 V

Selection option

A matched/balanced option is available on the BTB product page for suitable dual-channel and balanced applications

B9A base connections – bottom view

Pin 1

Cathode, internally connected to pin 3

Pin 2

Control grid g1

Pin 3

Cathode, internally connected to pin 1

Pins 4 and 5

Heater

Pin 6

Internal connection; leave unconnected in a new circuit

Pin 7

Anode

Pin 8

Suppressor grid g3 and internal shield

Pin 9

Screen grid g2

Design notes for phono and high-end audio

High transconductance provides useful gain but also demands disciplined construction. Short signal paths, effective anode and screen-supply decoupling and a grid-stopper resistor mounted close to the control-grid pin help prevent unwanted oscillation above the audible frequency range.

The equivalent RF noise resistance stated in the data sheet is encouraging, but it does not replace an audio-frequency test for hum, low-frequency noise or microphonics. A sensitive first phono stage benefits from a carefully selected valve, clean heater supply, shielding, thoughtful grounding and mechanical isolation.

For an MM cartridge, the cartridge inductance must be considered together with the total input capacitance of the valve, socket, wiring and interconnect. With a very low-output MC cartridge, the E180F can be particularly useful as the following gain, equalisation or driver stage after a suitable step-up transformer or separate low-noise input stage.

Triode operation gives the valve a comparatively low plate resistance for a high-gain device, making it useful as a driver or high-impedance preamplifier output. A loudspeaker, low-impedance headphone or 600 Ω load still requires a suitable transformer, buffer or other impedance-conversion stage.

BTB's selectable matched/balanced option is relevant to stereo channels, differential gain stages and balanced circuits that benefit from two valves with similar operating characteristics.

Safety notice: The 6.3 V heater rating is not the anode-supply voltage. Valve circuits may contain lethal voltages and should only be constructed and tested by suitably skilled users.

Questions about selection and audio use

Is the E180F / 6688 suitable for a high-quality phono preamplifier?

Yes, its high transconductance and useful noise characteristics make the E180F an attractive valve for a purpose-designed phono stage. It is particularly suitable as a second gain stage, RIAA driver or output stage; it can also serve as a first MM stage when input impedance, capacitance, heater supply and overload margin are properly engineered and the individual valve has been checked for noise and microphonics.

Is the E180F a worthwhile DIY alternative to the D3a, E280F, E810F, C3m or C3g?

Yes, the E180F offers the same broad appeal of professional construction, high transconductance and strong performance in input and driver circuits. It is a design alternative rather than a direct substitute: the D3a, E280F and E810F have their own pinouts and operating conditions, while the C3m and C3g use B8G Loctal bases and different heater ratings. For a new build, the E180F can therefore provide an especially interesting value-focused starting point.

Can the E180F be used as a driver, line stage or preamplifier output valve?

Yes, when triode strapped the E180F provides 21 mA/V transconductance, an amplification factor of 50 and approximately 2.4 kΩ plate resistance. This is useful for driver stages, high-impedance line outputs and transformer-coupled outputs. Pentode operation adds substantial voltage gain, while BTB's optional matched/balanced selection is attractive for stereo and differential circuits.