It’s been a productive few days. Two different amp projects are coming along nicely and today I’ve reached a milestone.

The 6AS7 SET

The first item of note is that the decisions are finally complete on the 6AS7 SET and things are moving forward. I have decided that the gloss on the chassis needs to be toned down. I have some finish conditioner I’ll be using to get a low luster finish. I will also add a buffed paste wax finish on top of that for a more aged look. I have to let the oil harden some more before that happens however. I probably won’t even attempt that until mid next week at the earliest.

I have also been making progress on the painted finish for the bottom and back of the SET. Temperatures have finally risen to the point where I can apply thin coats of paint and the finish is coming out well. The finish on the back plate will likely have to harden for a week or two before I can mount parts. However, the bottom can be left alone for weeks because it’s the last step before formal testing. The next post on the SET will probably be showing the first steps in assembly.

The 6L6 SE-UL

With the change in the volume control I talked about yesterday, the schematic design for the 6L6 SE-UL is complete. I have also done the design work necessary to ensure that the amp can use the other members of the 6L6 family, the 5881 and the KT-66, as well as the bigger KT-88/6550 without any parts change out. I have also made sure that the amp can use either the regular 6SL7GT or the 6SN7GT for lower sensitivity in the driver slot.

I have ordered the output transformers from Edcor as well. The 6L6 SE-UL will use the GXSE151-5K transformers. I chose the 15W versions due to the total current draw of the KT-88. The 10W transformer is limited to 80mA of bias current whereas the 15W is rated for up to 100mA. The test case with the KT-88 drew a total current of 76.1mA. I thought that the additional margin of the 15W was called for. The 15W also has a higher primary inductance that, with the typically higher plate resistance of the beam power tubes in UL, will result in a better low end response than the 10W without sacrificing the “speed” of the amplifier.

Other Items of Note

Today is the first anniversary of my retirement from my Engineering career. Some may have noticed an uptick in the number of blog posts in the last several months. The adjustment has not been without its challenges but overall I think I’m adapting nicely. And I am getting more and more time to devote to my tubes.

I am still looking for suggestions for projects or articles. If anyone has a project they’d like to see or a topic about which they’re curious, please drop me a line. It’s as easy a cliking the “contact me” link on the “About Me” page.

That’s about it for today. Time to get back to work.

As always, questions and comments are welcome.