Tube of the Month : The 5Z3

 Hi!

After the recent introduction of the ELROG ER5Z3, I thought it is a good idea to pick the 5Z3 as tube of the month.

The 5Z3 is a directly heated full wave rectifier. It is electrically identical to the 5U4 but has a different base.

While the 5U4 comes with a 8 pin Octal base (of which 4 pins are not used) the 5Z3 is the same tube on a 4 pin UX4 base. The pinout is shown on the left. Both tubes have a 5V filament which consumes 3A. They have the same maximum ratings and characteristics. See the RCA data sheet for all technical details. The 5Z3 is a member of a small family of 3 tubes which share the same electrical characteristics and only differ in the base. The third one is the 5X4 which has the same base as the 5U4 but a different pinout. While the 5U4 has seen a widespread use and still is used a lot in current production amplifiers, the 5Z3 and 5X4 were less popular and are rarely used nowadays. Let's have a look at some 5Z3 rectifiers from different manufacturers, starting with RCA:

Another RCA 5Z3 made for the military:

The military designation of the 5Z3 is VT-145

Next we have a National Union 5Z3:

Philco:

And lastly the ELROG ER5Z3, the only current production 5Z3 I am aware of:

Best regards

Thomas

Tube of the Month : The 5U4

 This month I'd like to introduce another full wave rectifier tube, the 5U4.

The 5U4 is probably one of the widest used directly heated rectifier tubes and is still in production today.

It shares the same octal pinout with the 274B which was presented last month. But it can handle more current, especially more peak current which enables the use of larger load capacitors directly after the rectifier. Although choke input filters are the better solution and are easy on the rectifier, cost saving measures forced amplifier designers to work with cap input filters and larger capacitors instead. While the 274B allows 4uF load capacitance, the 5U4 can handle 10 times that, 40uF. But the actual limiting factor is not just this cap value but the steady state peak plate current the tube can handle. As long as this value is not exceeded, the actual capacitance is of secondary importance. The 5U4 can handle a whopping 1A of peak current. This of course comes at a cost and requires a heftier filament. The 5U4 needs 3A filament current. See the General Electric datasheet for detailed technical parameters. Like the 274B the 5U4 also has a 4 pin counterpart which is the 5Z3. There is also a variant which is technically the same, also has an octal base but a different pinout. That is the 5X4. The 5U4 was made by all the major tube manufacturers and is still being made today among others by ELROG.

Here we have a 5U4G made by RCA.

The top:

The base, unused pins are left out to reduce creepage paths for high voltage.

Here we see the 'ribbon' filament:

Next we have a National Union:

A Raytheon 5U4G in plain military box:

Another RCA, also in military packaging:

The box also shows the military tube nr, VT-244

And lastly the newly released ELROG ER5U4G:

Like all ELROG tubes the ER5U4G uses a thoriated tungsten filament.

If you consider using the ER5U4G note the size difference to traditional 5U4 tubes:

Best regards

Thomas