All rights of photos and text reserved. Usage of photos or text from my blog on other websites or for any other purpose only with prior permission. If you want to use any material from my blog please contact me by email.

Saturday, July 13, 2013

Tube of the Month : The 5X4


This months tube is a rectifier tube, the 5X4:

This is a 'classical' rectifier as used in most tube rectified amplifiers. It has two diodes with a common cathode in one bottle. The rectifier is directly heated which means the filament is also the cathode.

The 5X4 was only made in ST glass as far as I am aware. That's why it is also called 5X4G. It has an Octal base. The pinout is shown on the left. It is typically used with a transformer with a center tapped secondary. The secondary connects to the plates of the rectifier and the center tap serves as ground. B+ is then derived from the center tap of the heater winding, or from either end of the filament. It can also be used in a bridge rectifier arrangement without center tapped secondary, if it is augmented by two additional diodes. These connect from the secondary ends to ground, cathodes to AC and anodes to ground. I mostly use TV damper diodes as rectifiers, that's why I have not used the 5X4 in any of my designs yet.

The reason why I am presenting it here in the tube of the month series is it's electrical equivalence to the very often used 5U4. It only differs in the pin out. 5U4 or 5U4G are often seen in the power amplifiers of 300B amplifiers. Hence they are commanding a hefty price. The 5X4 however is still largely overlooked. It typically costs a third or even less of the price of 5U4s.

Sockets which are wired for the 5U4 can be very easily rewired to accept the 5X4. While the plates of the 5X4 connect to pins 3 and 5, the 5U4 has the plates brought out to pins 4 and 6. The former has the filaments at 7 and 8 and the latter at 2 and 7.

The rectifier socket can even be wired such that it accepts both tube types. All that is needed are 3 jumpers which connect pins 3 with 4, 5 with 6 and 2 with 7.

The first photo above shows Rogers 5X4G made in Canada. Here some more details of this tube:

A Sylvania, made in USA:

A close up of it's ribbon filament:


RCA slightly changed construction details and printing over the years:

A close up of the filament of a RCA tube:

Availability of the 5X4 is still good. If your amp uses 5U4 rectifiers and you have difficulties finding replacements, consider modifying it to accept 5X4.

Best regards



  1. Dear Thomas
    Today on the web we have so many egocentric hi-fi blogs in style look at my bling super bucksamplifier or "esoteric" and no more to learn :-(
    VinylSavor is other world its make my realy happy OOUPII:-)
    article about rectifier 5X4 is one perfect example:
    great explanations,
    delicious photos , very USEFULL & PRACTIC informations.
    Thank a lot sir Thomas Mayer for generosity to share this for diyers
    Have fun

  2. Dear Thomas,

    This is a nice blog. I was going through each page of this blog and came across one issue The webpage for 5U4 brings 5X4

    http://vinylsavor.blogspot.com/search/label/5X4 and http://vinylsavor.blogspot.com/search/label/5U4 are displaying the same page.

    Thank you,


    1. Hi!
      No this is correct Since the 5X4 article mentions how to replace the 5U4 with it, the 5U4 label also points here. No other posts about the 5U4 have been written so far, that is why it only points here.