Early anode current test setup for ECC81 types and equivalents (CV455 , CV4024, 6201, 6679, 6060, 12AT7)
At the start of this site the standard ECC81 family tubes were tested in another way. The anode current (Ia) was tested with: Va = 250V end Vg= -2V. Measurement after 10 minutes stabilization. Rated value new ECC81: Ia = 10mA. When tubes in the shop are tested with this setup it is specified in the description.
The disadvantage of this test set-up is that the manufacturers quality criteria do not apply for the obtained tube data. The factory quality criteria are valid for measurements with the manufacturers test set-up only.
Therefore presently all tubes of the ECC81 family are tested with the factory test setup as specified below;
Anode current (Ia) is tested with the Telefunken/Philips/Mullard test setup: Va = 250V in conjunction with a 200 Ohm cathode resistor. Measurement after 10 minutes stabilization. Rated value for a NEW tube: Ia = 7 to 14 mA.
Mutual transconductance (Gm or S) tests are done with a 10% Vg signal. Rated value for a new tube: Gm= 5,5 ± 1 mA/V.
Gas and shorts are tested with: AVO CT-160 (Dutch army tester) Setup: AVO Valve Data Manual 23rd edition 1981.
End of life data: Ia = 6 mA, Gm = 3,8 mA/V.
ECC-type twin triodes are very popular for audio applications. The most sought after makes are from Telefunken Berlin, Philips Heerlen, Valvo Hamburg, Mullard UK and Siemens Munich. Phillips Heerlen is sold under various names among which Adzam, Valvo, Amperex, etceteras.
Philips, Mullard, Philips, Telefunken and other manufacturiers describe how to measure the tube data of a premium ECC tubes. And they supply clear end of life criteria for these tubes. These criteria are more consistent and strict than those used in traditional tube testers. For example: the rated anode current of a new E88CC is 15 mA and the end of life is reached when this value is lowered by 10% (13,5mA). In many tube testers the end of life is indicated when the initial value has lowered by 40% (9 mA) or more.
For our tube tests and ratings of the ECC81 family we use the test setup and the very strict NOS and end of life criteria that are specified by the manufacturers (Telefunken, Philips, Siemens, Mullard, …).
The specs of a premium ECC81 (e.g. ECC801S), testing setup and end of life criteria as supplied by the manufacturers are shown hereafter.
The pictures are an abstract from the official data sheets.
Please note that for the anode current and S (Gm; mutual conductance) also a maximum value is specified!