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Monday, September 27, 2021

Tube of the Month : The ECC88 / 6DJ8


This month I am presenting a 9 pin miniature (Noval) medium mu twin triode. Meet the ECC88:

The ECC88 is one of the more popular tubes among tube amplifier manufacturers and has seen some widespread use. For example some Audio Research preamplifiers use this tube.

With an amplification factor of 33 it is classified as a medium mu triode. The Noval base shares the same pinout with other popular ECC family tubes as the ECC83, ECC82, ECC81 or ECC85. The pinout is shown on the left. What makes the ECC88 stand out among the others is the rather high transconductance of 12.5 mS. As the prefix 'E' indicates it has a 6.3V heater which consumes only 300mA. For all technical parameters see the Telefunken data sheet. I never really used the ECC88 much in any of my own projects. For my applications the amplification factor was a bit too low or the plate resistance somewhat too high. Or the available output voltage would not provide the headroom I wanted. But that doesn't make it a bad tube. In contrary, if the parameters fit the application I would not hesitate to use it. The ECC88 was made by all the major European manufacturers and also came in industrial or rugged flavours with enhanced life time, tighter parameters and other improvements. These were called E88CC or CCa. The American equivalent was the 6DJ8 which had an industrial variant as well, called 6922.

As always we start with a look at the plate curves. Datasheet curves above and measurement of an actual tube below.

A very linear tube, which explains the popularity.

Since I never really used the ECC88 I did not accumulate a large stock of them. Above is all I have.

Starting with what is probably the most sought after version, the Telefunken E88CC with embossed diamond logo in the base.

Made at the famous Telefunken factory in Ulm.

Siemens E88CC:

Siemens-Halske tube in US military packaging:

E88CC made by Valvo:

And lastly a JAN 6922 made by Philips ECG:

And closing the post with a tube in operation:

Best regards


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