To my point of view, ECC40 is one of the best double triodes for audio use. Small problem is B8A Rimlock socket. Almost all versions are round plates and silver plated pins! Characteristics are very interesting, somewhere between ECC82 (12AU7) and ECC83 (12AX7) and almost all ECC40 I tested are low microphonics. In phase splitter aplications this tube is simply unbeatable!!!
I transformed my Williamson amplifier with 807 (EL34 / 6CA7) KT66 and now use just one ECC40 instead of two 6SN7GT with great results.
“The ECC 40 is an indirectly heated double triode, of which the two sections, apart from the heaters, are completely separate. This valve is intended primarily for use as an A.F. amplifier and phase inverter, but is also suitable for other purposes, for example as an oscillator, frequency changer, blocking oscillator, etc. in u.s.w apparatus. It is also being more and more widely used for electronic counters and calculating and accounting machines. The fact that the valve would often be called upon to meet much more stringent conditions than when used for normal A.F. amplification was taken into consideration in its development: to mention only one factor, the maximum permissible voltage between hea ter and cathode is 175 V, whereas a maximum of 50 V is usually high enough for E-type valves intended only for use in ordinary amplifiers and broadcast receivers. The amplification factor of each section of the ECC 40 is 32 and the mutual conductance 2.9 mA/V; each section is therefore capable of providing a reasonable gain while it will also function efficiently as an oscillator. The heaters of the two sections are connected in parallel and, as the heater current is 0.3 A in each case, the total heater current is 0.6 A at a voltage of 6.3 V. … ”
British equivalent is CV3884. Glass envelope is 20 mm in diameter and, excluding the base pins, is 60 mm tall.
If anyone has Telefunken ECC40 with diamond logo in the bottom I’d like to swap some of my tubes for them.
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