The XLS Series tubes are based on an extra large size (XLS) Anode system. This system is taken from earlier EML 52B tubes, and has proven to be ideal for high power applications.
The EML 320B-XLS is a version of the 300B-XLS with higher peak emission. In cases where this extra emission is not required, the 300B-XLS is the better choice. The higher peak emission of the 320B-XLS results from the higher heater current of this tube. Specially for Push Pull amplifiers, 320B-XLS is "the" choice. However it needs to be checked if the amplifier can supply the higher heater current needed. Another application is for Single Ended amplifiers that have their performance limits in the standard 300B tubes used, and not in the amplifier hardware itself. Such amplifiers can often already be recognized by the higher weight, such as the VAIC, Mastersound, and several others. These have a large power supply, well sized output transformers, and ideally the option to set the Anode current of the output tube.
A final application is for such amplifiers that seem to have low tube life with any 300B, regardless what brand 300B is used. Such amplifiers stress the tubes by default. The higher heater current of the 320B-XLS makes this tube more resistant against anything, and more lifetime as with standard 300B may be expected.
The EML 320B-XLS will bias like a normal 300B tube, when used in any 300B amplifier. When used like this, due to the stronger electron emission, this tube will develop the output signal with more ease. When biased higher than a standard 300B, the EML 320B-XLS will show more of it's superior quality. It will show a better dynamic behavior, and lower distortion at all power levels.
Heater Current Special Note:
The higher emission results from the higher heater current of this tube. It needs to be checked if the amplifier can supply the higher heater current, and still guarantee the heater voltage of 5Volt. Under heating of the 320B-XLS is definitely not allowed. It should be 5.0 Volt, with a tolerance of 5%. In case you have too low heater voltage by mistake, the tube initially performs well, however bias problems will occur after a few hundred hours. If you are not sure if the higher heater current can be supplied, you should check the heater voltage with a voltmeter. You need 5V with 5% tolerance. For the rest there are no restrictions, and this tube can replace any 300B or 300B-XLS directly.
All critical parts, like heaters, grids and Anodes are constructed of hard metal for higher reliability and reproducible quality.
PUSH-PULL special note:
Push pull with (any) DHT is much harder for the tubes than SE. You may easily see low quality 300B fail in PP amplifiers. The higher heater current of the 320B-XLS allows higher Anode current peaks, and this makes the tube so well suited for Push-Pull amplifiers.