Tube of the Month : The 6X5

Hi!

This month I'd like to present another small rectifier suitable for preamps. I have mostly been using the 6BY5 for that. Last year I introduced the 6AX5 which has the advantage of lower heater current. There is another rectifier which needs even less heater power, the 6X5.

With it's moderate 0.6A heater current this tube is perfect for use in preamps when space is restricted and only small power transformers can be used.

The tube has an octal base. The pinout is shown on the left. Like the 6AX5 it is a full wave rectifier with two plates and a single, common  cathode. It can deliver up to 70mA of DC current and up to 400V output voltage which should be good enough for most preamplifiers. See the data sheet for all technical parameters. The tube would be good to be used in my Octal line preamplifier or Octal phono preamplifier. Other suitable applications would be in power amps which use separate supplies for driver and output stage. The 6X5 could power the driver and/or input stages. If space is restricted the 6X4 could be used instead which is very similar but in a smaller envelope and on 7 pin miniature base.

The 6X5 does not seem to be used a lot by amplifier builders, hence availability of NOS tubes is good at low prices. The tube can be found from all the major brands of the vacuum tube era. Let's have a look at some of them.

RCA 6X5:

Cunningham, made by RCA:

Sylvania:

Another Sylvania:

One more in the more modern Sylvania packaging:

This later tube has a different internal construction as the older ones. Here the two in comparison:

A militay tube, JAN (Joint Army Navy), also made by Sylvania:

Philco, probably also made by Sylvania:

Another Philco, this one looks as if it was made by RCA:

Tung-Sol 6X5GT:

General Electric:

The GEs are shorter and more compact than the others:

The construction styles (arrangement of the plates) varies considerably. This one has the two plates arranged at different heights:

And this one side by side:

In the second tube it almost looks like there is only a single plate, so let's open one up to see how it's done:

A close up shows that there are two separate plates:

The two plates removed:

Let's examine the other construction style:

A close up of heater and cathode connections:

Removing the upper plate:

The cathode with the heater wire partially pulled out:

Cathode and heater:

A great tube which deserves to be used much more!

I hope you enjoyed the first tube of the month presentation of this year.

Best regards

Thomas