Tuesday, November 25, 2008

EF40 - the rimlock version of the EF86 pentode

For anyone using the EF86 pentode, NOS tube prices have been rising! What to do? There are new production tubes out there - the discontinued Svetlana EF86 which has a harsher top-end than an old Euro tube. The EH EF86 is pretty good, though it seems to lack some music 'color', reminding me of solid-state. I have yet to hear the latest JJ version - prices are still high on this model.

Back in 1948, Philips introduced the rimlock EF40 tube which was the precursor to the EF86. This tube was used in several pieces of Siemens theater gear and in Philips radios. What makes the EF40 different than the EF86? In this case it is just the base - the EF40 (along with several other excellent tubes - notably the ECC40) uses a B8A socket. The B8A or rimlock socket uses a nub on the side of the tube which centers the tube in the socket. Kind of neat bit of engineering and also forces good contact with the pins. The B8A rimlock socket was eventually discontinued as the majority of small tubes went to U.S. standards. Therefore B8A tube sockets are available mostly through European dealers and can also be found on Ebay. Avoid the Chinese sockets as they do not have the metal outside base to center the tubes.

Who manufactured the EF40? Sorry - no GEC or Telefunken here - just Philips (branded Mullard, Valvo, etc) from Holland and (seems to be mostly) France. Earlier versions were made in the Netherlands while perhaps production was quickly be moved to France. Later 60s production was made by Tungsram. There are also Siemens versions out there but I have yet to hear a pair and I've suspected they are actually Philips since they have the same construction. I do have a single Siemens supposedly made in Germany - I would like some further confirmation on this. Check out a nice gallery here of EF40s.

Best sounding are the Holland versions followed by the Tungsram. In general the French versions seems to lack the last bit of finesse of the Holland ones - and I've found this true even for EF86s - but the French versions are still very good. Tungsrams have good slam/dynamics. All versions seem to be very low in microphonics - perhaps it is the rimlock socket holding the tube tightly. The rarest (and earliest) versions feature a metal base for the nub and a solid metal screen. Within a year or two the the centering nub was included as part of the glass.

Going prices of the EF40 make them bargains! I've paid anywhere between $2 to $8 each. Provided the socket to be replaced is hardwired, it would only take a little work to convert to use the EF40. Not many of these show up in the U.S, but Canadian and European sellers have them and would be happy if you took them off their hands.