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Wednesday, November 22, 2017

Tube of the Month : The 17AX4


This month it is TV Damper tube time again! Let's have a look at the 17AX4.

As the name implies, the 17AX4 is a variant of the 6AX4 with different heater voltage. All other parameters are identical to the of the 6AX4. I already showed another heater variant of these, the 25AX4.

It also shares the same pinout. The 17AX4 was designed for series heating which was commonly done in TV sets. Several tubes with the same heater current would be hooked up in series. The nominal heater voltage of the 17AX4 is specified at 16.8V and it draws 0.45A. Since tubes with odd heater voltages are not very popular nowadays such tubes can be picked up at very low cost. If the exact heater voltage is not available a higher AC voltage can be simply reduced with a suitable dropping resistor. These will perform just as well as other TV Damper tubes. Since I have plenty 6.3V heater TV  dampers, I only stocked up a few of these, made by General Electric and Sylvania. But they have been made by many other manufacturers as well. Let's start with the Sylvania 17AX4:

Among this small heap of tubes there are several different variants. Here a closer look:

The top:

Another one:

These all came in the typical yellow boxes:

The tubes and boxes have dual markings 17AX4 and 17DM4:

It was common practice to stamp tubes with several designations of variants with the same characteristics.

Next a 'coin base' type:

General Electric 17AX4:

Here a 6AX4 and 17AX4 side by side.

Now let's open this one up to see the internal construction:

Glas removed:

Close up to the plate:

The connections at the bottom:

The top:

The heater removed from the cathode:

The spiral around the heater provides the necessary distance and isolation to the cathode.

The spiral removed from the heater wire:

The cathode:

Cathode, heater and insulation spiral:

The plate:

Here we see the plate opened up:

And finally some photos of a tube with the heater lit up.

Close ups to the top and bottom:

That's all for the 17AX4.

Best regards



  1. I believe if memory serves there was also a 12AX4?

    1. Hi Daniel,
      yes there is also a 12V variant