Rectifier Tube : Do I Need This Thing?

[jhendow]

I have an original 100 watt Lonestar, which I love love love. I never use the 5U4 tube rectifier because I always have the amp in 100w mode, which automatically switches in the solid state rectifiers. In the past month the amp suddenly died at a gig. Apparently my power tubes went to heaven and blew the amp's fuse. I took the amp to the shop and had it checked out; all it needed was a new fuse and a new fleet of power tubes. I didn't replace the rectifier tube because I never have the amp in tube rectifier mode. Two weeks later the fuse blew again. I took it back to the shop and my amp tech informed my it was possibly the rectifier tube, even though it's technically not in the circuit. We bench tested the amp and sure enough, even when the amp is in solid-state rectifier mode, the tube rectifier is still getting several hundred volts. I have a replacement Boogie 5U4 but my tech told me just to use the amp with that socket empty. It seems weird to me to have an empty socket so I'll probably wind up putting a plug-in solid-state rectifier in its place just so it's safe if someone accidentally switches it over to the "tube rectifier" position on the back. Is this an unusual behavior for a modern tube amp? I know the trend in modern amp design is to omit tube rectifiers in favor of more stable / reliable solid state rectifiers. I'm interested in hearing if others have had similar experiences.

 

[ricardo loma vista]

I've had the same experience on a LSS, which uses a solid state rectifier on 30W mode, and tube rectifier on 5/15 watt mode. The first time my rectifier tube failed, I was on the 15 W mode, so I replaced the fuse and switched to the 30W mode. Within 10 minutes the fuse blew again. I pulled the rectifier tube out of the socket, replaced the fuse again, and finished the rest of the evening without problems.

To avoid warm up times when the amp switches from one mode to another, the rectifier tube is still pulling current and ready to go. If there's a short in the rectifier tube, it can draw enough to blow the fuse even though the amp is using the solid state rectifier.

You can safely run the amp without the rectifier tube. If someone switches it to rectifier mode, all that will happen is that you will get no sound.

You can also replace the rectifier tube with a NOS tube. NOS tubes are a lot more relaible than modern tubes--even if they say "Mesa" on them.

Solid state rectifiers are definitely more reliable than tube rectifiers, but a lot of people like the way a tube rectifier makes the amp sound--because the tube rectifier responds more slowly to power demand, there's a "sag" from a tube rectifier when you really push the amp. Solid state doesn't exhibit any sag. However, one company (I think Weber) makes a solid state rectifier that is supposed to sag like a real tube rectifier, but I've never tried one.