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Monday, January 16, 2023

Tube of the Month : The EF6


Last Month we had a European triode. This month we stay in Europe with the presentation of a pentode. Meet the EF6.

Niclas of Sweden contacted me after my appeal to help keeping the tube of the month series alive. He sent several different interesting types which I do not have. Hopefully others will follow as well and lend me some tubes to take photos.

I am starting with an indirectly heated pentode form Niclas' care package. The EF6 which was developed for use as audio amplifier or grid detector. It has a P-Type side contact base and a top cap which is connected to the control grid (g1). The pinout is shown on the left. The EF6 has a rather unusual appearance due to its bright red coating. Underneath the red coating there is a metallisation for screening the tube. The tube has a 6.3V heater which only consumes 200mA of current. You may refer to the Philips data sheet for a full set of technical specifications. In the data sheet the low distortion of the tube is mentioned and capability to deliver large voltage swings suitable to drive output tubes. The data sheet shows a set of plate curves in triode mode which indeed looks impressive:

Taking the curves from an actual sample required hooking up the tube with clip leads due to lack of a suitable socket.

Definitely an interesting tube. Especially if you are keen on using less common types in your projects. I will return the tubes which were lent to me so no project from me in sight using the EF6.

Here we have a EF6 made by Valvo.

The base:

A small area around the grid top cap remains uncoated in order not to short out the signal.

Some details of the box:

Next we have a Philips EF6:

And lastly a EF6 made by Tungsram:

Due to the coating no glow is visible when the tube is in operation. Also no dissection of a tube since they do not belong to me and it would be a shame to sacrifice any of these beauties.

Hope you enjoyed this first tube presentation of 2023. many thanks to Niclas for lending me these tubes. I hope more people will follow his example. Rest assured all tubes will be returned promptly after taking the photos.

Best regards



  1. Guten Morgen Thomas,
    ich werde heute nach der Arbeit meinen Röhrenbestand durchsehen
    und dir dann Bescheid geben was da ist.
    Grüsse Hannes

  2. Happy new Year Thomas! A really good post to begin 2023. Looking forward with anticipation the unusual/unique tubes you can come up with this year. All the best to you and yours in this New year. Randy/GA