Not just an replacement, but an improvement!

This tube has the classical grid construction and the tube curves of the 300B. It has the stronger plate construction and larger glass of the vintage 52B however. So in one tube we have combined the very best of two classical products.

Sound Character of the 300B-XLS tube

For use in Push Pull amplifiers, this is always the tube of choice, because this type of amplifier is hard on the tubes by definition. The 300B-XLS is made to deal with such conditions, and will allow the amplifier to play gently at low sound level, as well as reproduce higher sound level with the detail and precision you expect from a push pull amplifier.

For use in Single Ended amplifiers, the 300B-XLS is the best choice, since with those amplifiers good sound is coming from the right use of the tube, not over stressing the tube. The right use means, the tube should not be working at it's maximum electrical performance. Here we think the 300B-XLS is at it's right place, taking advantage of the higher electrical reserve this tube has. The 300B-XLS will reproduce the required loudness with more ease than the standard 300B. The result is a more transparent sound picture at low or medium volume, while at higher volume, the dynamics of the original recording will stay unaffected.

The 300B-XLS will bias in any amplifier the same way as the original WE300B. Sill it can be used in two ways if you want it.  These two modes are explained here.

1) You can replace any 300B with this tube.  Just plug it into any 300B amplifier, and the tube will set  itself exactly  to the original 300B working point. The EML 300B-XLS is is a very strong tube,  and it will develop the output power with more ease.  Specially for amplifiers that let the 300B tubes work very hard, the EML 300B-XLS is the right product  to choose. Any amplifier that is trying to get as much as possible power out of a normal 300B, will benefit from the 300B-XLS. Improved sound and longer lifetime will be the result.

2) Another   purpose of the EML 300B-XLS is to get more power,  than is possible with standard 300B tubes.  This can only be done when you have the possibility to adjust the settings of the amplifier.  If you increase the plate current of the tube ABOVE the standard 300B specifications, something very special will happen.  The tube  will now move to a part of the curves where it has a lower plate resistance. This is a specialty of the 300B-XLS. This will give a better damping factor of the bass and mid range loudspeakers, resulting in a more natural sound. Check our customer feedback section of the website!

All critical parts, like filaments, grids and plates are constructed of hard metal for the best reliability and reproducible quality. 

We have two versions for the heater: Normal heater, or Center Tapped heater.

With the center tapped tubes, we enter a new field of applications. This has not been done before with Audio tubes. When biasing a DHT tube there is no cathode to connect something to. The cathode must be artificially constructed, by a resistor network. Since many years, all EML tubes already feature a center tapped heater, which is a way to enforce better electrical field geometry. Only, to this center tap there was never an electrical connection. So to the tube itself we had to make no changes. To the center tap of the heater, is now connected a wire, which becomes the third connection to the heater. Now the tube has five wire connections, and for this reason we can not use the 4 Pin UX4 base any more. We have chosen for the Octal base. It must be said, the V4 is a very special tube, which fulfills the needs of Circuit Design purists the best possible way. Depending on how you do it, you can enter new design fields, or you may choose to connect the center tapped tubes just the classical way. Even so, for tube testing you can ignore the center tap, and just connect the tube the regular (four pole) way. In that case, the EML1605-V4 will behave like a standard four pole tube. In the case you own center tapped tubes, but you whish to connect them like a non-center tapped tube, this is possible too. In that case just do not connect the center tap.

Later, an application note will be issued. At the moment, this information is here.

Recommended transformers

Single Ended: LL1623-90mA (Wire secondary for ALT B, C, D for : 4, 8, 16 Ohms in this order) Single Ended: LL1623-120mA (Wire secondary for ALT B, C, D for : 4, 8, 16 Ohms in this order) Single Ended: LL1664-80mA (Secondary 8 Ohms) Complete list of recommendations here

Features

• Gold plated, Wolfram Grid
• Soft rubber suspended tube base
• Center tapped filament (Note5)
• Slow Start filaments, for best lifetime
• Double Mica tube top
• Hard metal Construction (Note1)
• Two extra large getters
• Hand blown Glass bulb
• Anti-microphonic plate- and grid  suspension
• These tubes are shipped in a high quality dual box
• Tube printing with real gold (metal),  red color is glass burned into the glass 
• Machined, solid tube base pins for highest contact precision. YAMAMOTO tube sockets highly recommended. 
• Gold plated pins,  black ceramic socket.  (White bottom.)

• Note 1)  Hard-metal filaments prevent filament breakage with DHT Tubes.  This material has a higher melting point than the classical nickel wires. Hard metal plates have a more precise plate distance, and do not change shape when heated.  This ensures  reproducible tube parameters, and long term stability. Wolfram grids  allow the most precise grid wire distance, because wolfram is an extreme hard metal.   This ensures better uniformity and linearity at the low end of the tube curves.
• Note 2)  Individual Test data, such as:  Matching Data, Grid Current, Vacuum, Filament Current, etc.,  are on the Certificate that comes with each individual Tube.  Each tube  is numbered, inside the bulb  with a metal Tag
• Note 3)  Maximum specifications. These data are only to show the safety distance to the recommended operating point.   You can operate the tube at the maximum for a short period of time.  Exceeding the maximum, will decrease the lifetime  very rapidly.  For absolute maximum lifetime, choose the working point from the the "typical"  dissipation  (green table) 
• Note 4) We are recommending the same values as Western Electric in their 1950 Data sheet.
• Note 5) A center tapped filament indeed has a real center tap in the middle, which much be constructed in a symmetrical way. The center tap can be seen when looking inside the tube, only electrically there is no socket pin connected to it. The result of a center tapped filament is, each filaments has the current flowing in the opposite direction of the adjacent filament. So the current direction is for the eight filaments: + - + - + - + - (eight times). For a non-center tapped filament it is: + - - + + - - +. Specialists know that the grid field gets always somewhat distorted by the heater (filament) field, resulting is some tube hum when the tubes get older. With a center tapped filament this effect is much less. Also the tube curves will benefit from this somewhat. This is the best way we can explain it by text only.