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Saturday, January 25, 2014

Tube of the Month : The 6X5


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:


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



  1. The 6X5, at least many of the older ones, have an unfortunate reputation for shorting and destroying the power transformers. This may be the reason it is not more popular.
    I love your website and have learned quite a bit here. Thank you!


  2. I've seen more complaints about the 6X5 shorting than praise for it. In fact this is the first time that I've seen it praised. I recently saw a recommendation to replace the 6X5GT with a 6X5WGT. Apparently it's an improved version of the 6X5?


    1. they short-circuit them because they put capacitors that are too large or they feed circuits that require too much current. I have seen people put 220uF capacitor and 470uF after 6X4 / 6X5 then complain that it fails, they are just stupid people.

    2. yes i have seen this .....even 220uf is way to much...40 do not go higher in uF..use a small choke with few H will do miracles as well.. use two one for one f.e.6SN7
      Since cheap only the transformer needs some extra wirings

  3. Hi!

    Thanks for this information. I never actually used 6X5 rectifiers myself. So I will be careful about this


  4. In the vintage radio world, the 6X5 has been known to short taking out a transformer. There are the newer 'safer' plate arrangements, such as the X plate or parallel config , or the military version that might have a lower failure rate. If you search some of the sites you can see that these tubes are frowned upon. Zenith did put out a service bulletin about the tubes, since many Zenith transformers were having to be replaced back in the day. GREAT article though showing the different types, and construction. Best regards.

    1. Hi! Several people have mentioned this already. Thanks for the info. I never used them myself so didn't run into this problem



  5. I have used these tubes - as a EZ35 with no problem. But then i must add that it has it's own dedicated heater winding that is not referenced to earth. I understand that the old Zenith radio's had the heater/ cathode at quite a voltage difference.