So, I was sitting here on this rainy Sunday morning going through some amplifier designs and looking through my stash of tubes and various amplifier building supplies. While standing there looking at the shelves of vacuum tubes, transformers, and various piece-parts, my eyes drifted up to an amplifier sitting on the top shelf. It was my 6AS5 µ-power UL amplifier documented here. But why was the little amp sitting on a shelf collecting dust? Then I remembered.

I built this little amplifier about five years ago as an experiment. I wanted to try out a different power supply topology to improve channel separation. So I put it together and used it for a time in my office. Then it got packed up and traveled across the country with me when I moved for work.

While in my new home, I took it out only once, and at that time, it didn’t sound “right” to me. There was something off and I didn’t have the time to investigate further. So I set it aside. Then, after less than 20 months, it got boxed up again and shipped back across the country when I moved for work again. With everything that has been going on the the last couple of years the amp had become, if not forgotten, then at least pushed down the priority list. This brings us to this morning.

On a whim, I pulled the little amp off the shelf. I pulled the tubes and cleaned the contacts and pins, wired up some speakers, and connected my iPod. I selected the same music with which I first tested it, “Gabriel’s Oboe” from Chris Botti’s album “Italia”. And the little amp came to life. The sound stage was deep and well separated, the tone full and balanced, and the overall sound warm and relaxing. I’ve been listening to it for a couple of hours now with a mixed playlist of instrumental and vocal jazz. And the little amp sounds wonderful. I don’t know what I thought was wrong the last time I listened to it (it might have been the very large room in which I tested it) but there is no hint of any problem now.

I guess this is just a reminder to not let yourself forget about past successes when getting excited about your new latest project. I could have left this amp on a shelf for years because of some vague idea about how I thought it sounded. But because I didn’t, I have rediscovered a nice little UL project that I really enjoy. I guess the lesson is that it really pays to revisit these past projects from time to time. If for no other reason than to remind us of the things we’ve done.

I don’t know what I’ll do with this little amp tomorrow, but one thing I know for sure; it will NOT be going back on a shelf to be forgotten!

A Quick Postscript:

After about 5 hours of playing I had a hiss/crackle/pop out of the left channel and then nothing from that side. Quick investigation reveled that one side of the 6CG7 preamp tube had given up the ghost. Perhaps that’s what “didn’t sound right” last time I had it fired up. Regardless, a quick replacement with a NOS GE tube from my stash, and the amp is singing once again.