Yesterday, after setting the B+ and installing the power supply dropping resistor, I tried out the 6AS7 SET. To say that I am pleased would be an understatement.

Today I’ll be putting the SET through some testing to determine peak power out, distortion levels, and total bandwidth. But yesterday, once it was operational, I couldn’t resist putting a little music through the amp.

Her’s the amp sitting on my work table playing its first music. The sound is excellent. It now has about six hours of operation on it and I simply cannot find anything I would change. I have thrown just about every type of music you can imagine at this amp and it all sounds great.

For the first break-in I’m running a JAN 6080WC in the power tube socket and two GE 5814As in the driver positions. Later I’ll replace the drivers with some matched 12AU7A tubes and I’ll try out some of my other 6AS7 tubes.

And for those thinking I’ve been shirking my test duties, I did get a full set of voltage measurements once I set the power stage B+ voltage. I used a 200Ω Rd to set the B+ for the power stages at 267v. The driver stage B+ voltages are running at 306v for both drivers. This ensures lots of headroom for driving the power stage to full power. Here are the bias operating point voltages with the break-in tube set installed.

The filament voltages look good. The power tube bias points are acceptable with plate dissipations running just a little over 12W on the plates and the bias resistors dissipating 6.5W and 6W on sections 1 and 2 respectively. Further, all the driver bias point are acceptable and per design.

Now I just need to stop listening to the SET long enough to do the testing.

As always, comments and questions are welcome.