It's been a long, long time since I've heard a single-ended pentode (SEP) amplifier. The popular thing to do is to use the 300B, but hey, I'm a cheapskate who still likes to use old tubes that are still as common as dirt. Enter the 1625 output tube and 12J7 driver which can still be had for a couple of bucks each. It's also been a few years since I've built a tube amp from scratch so it was even better when this amplifier worked from the very first time it was turned on.
Eagle eyed members of this site will recognize the general basics of this amplifier from a single-ended ultralinear design by Electraprint. Oddly enough that design wasn't my original inspiration, but instead it was the classic jc morrison SEUL 6L6GC. However I went with a higher B+, pentode connection, and a much different power supply cobbled together with some cheap Allied iron, Triad chokes, and VR regulation for the screens and input stage. Lots of the parts were also from my tub of "junk parts", so that's explains some of the odd part values. It also kept the build cost under $600.
LOTS of potential for improvements here - and I'm sure the usual suspects will weigh in for my mistakes or ways to make this simple amplifier even better. I can think of a couple of myself. But hey, the amp works and sounds quite nice as-is. I am, however, not too pleased with the quality of the Chinese ceramic plate caps for the 1625. I'll be hunting for some NOS versions instead - like I used for the 12J7. The UX4 Johnson Chinese ceramic socket isn't too great either, since it allowed me to plug in the tube 90 degrees off, resulting in some headscratching when the amplifier blew a fuse upon turn on.
I live in a fairly low RF area, but I would probably add in some type of plate stopper for the 1625. Full build details and some further listening tests against my rebuilt EICO HF-60s are on my blog.
6th Street Bridge: Project: The Command 1625 tube amplifier
Eagle eyed members of this site will recognize the general basics of this amplifier from a single-ended ultralinear design by Electraprint. Oddly enough that design wasn't my original inspiration, but instead it was the classic jc morrison SEUL 6L6GC. However I went with a higher B+, pentode connection, and a much different power supply cobbled together with some cheap Allied iron, Triad chokes, and VR regulation for the screens and input stage. Lots of the parts were also from my tub of "junk parts", so that's explains some of the odd part values. It also kept the build cost under $600.
LOTS of potential for improvements here - and I'm sure the usual suspects will weigh in for my mistakes or ways to make this simple amplifier even better. I can think of a couple of myself. But hey, the amp works and sounds quite nice as-is. I am, however, not too pleased with the quality of the Chinese ceramic plate caps for the 1625. I'll be hunting for some NOS versions instead - like I used for the 12J7. The UX4 Johnson Chinese ceramic socket isn't too great either, since it allowed me to plug in the tube 90 degrees off, resulting in some headscratching when the amplifier blew a fuse upon turn on.
I live in a fairly low RF area, but I would probably add in some type of plate stopper for the 1625. Full build details and some further listening tests against my rebuilt EICO HF-60s are on my blog.
6th Street Bridge: Project: The Command 1625 tube amplifier