520B V3 (UX4 Base) is in stock and will ship quickly.
520B V2 and V4 are special order directly from Emission Labs with a typical 2-4 week delivery time.
If buying this as a replacement tube, please review this page prior.
If you believe you need a 520B V2 (6.5v Version) please contact us so that we can special order for you.
The 520B is a long Anode Version of the older 52B, with many technical improvements added. The EML520B is a state of the art product, in the family of the 300B tubes. This powerful tube is recommended for new designs. The 520B has the same outside dimensions as the "845" tube, but longer Anodes. All critical parts, like filaments, grids and Anodes are constructed of hard metal for higher reliability and reproducible quality. Note the relation between the tube base, and and the glass bulb. Then compare this with our 300B. This gives you some idea of this tube's size.
520B-V2 6.5V Filament Originally made for some amplifier manufacturers. No stock item any more in 2018, but can be build on order if needed. Tube will not be obsoleted. 520B-V3 5V Filament Standard tube since many years. 520B-V4 5V Filament with Balanced Heater Special version for improved bias scheme. Read application note AN06.
Read More Here: http://www.emissionlabs.com/datasheets/EML520B-Datasheet.htm