PX4 - Similar Valves

The PX4 was a development of the M-OV P410 valve. It is the standard by which all other triode power valves are judged, so you might expect that it would have some rivals and imitators.

  • PP3/250. A Mazda valve, this pre-dates the PX4 and was used in the output stage of many early wireless sets. Electrically, it is equivalent to an early PX4.
  • AC044. Made by Mullard, the AC044 is an equivalent of the PX4, but without such a good sound.
  • LP4. Marketed by Ferranti, early (pre-WWII) LP4's came from a variety of sources while post WWII LP'4s are thought to have been badged PX4's. The British valve manufacturers often indulged in such badge-engineering.
  • PX25. This also is a product of Marconi-Osram, and is more powerful than the PX4. Most people believe it to be a high-power development of the PX4 (the naming implies this, after all), but this is not the case. The PX25 was developed from the LS6A, and whilst it is an exceedingly good valve, its linearity and sonic performance are not quite in the same league as the PX4.
  • LK4110. Made by Valvo (Deutsche Philips) in Germany, the LK4110 is lower-powered than the PX4, but almost matches it in sonic performance.
  • 2A3. A product of RCA, the 2A3 is a fine valve. It was also manufactured under licence by Brimar in the UK and Fivre in Italy. There were mono-plate and bi-plate versions and I am told that the best-sounding 2A3's were bi-plate versions made by Fivre.