Copper

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.

I first announced this SET on September 18th, 2020. It’s only taken me about 19 months to get to this point. To be fair, that 19 months was fairly eventful, including both my retirement and much of the COVID madness. But tomorrow, the slow methodical process of testing can finally begin.

For the last few days I’ve been applying oil to the SET chassis. It now has four coats of oil, cured and buffed out. There’s only one decision left for the chassis.

It looks like the weather has finally broken here at CascadeTubes and spring has arrived. Yesterday, the 6AS7 SET chassis got its first coat of oil. The purple heart used for this chassis is definitely much deeper in tone than that used on the The 6DJ8 Headphone Amp.

It’s been a tense couple of days waiting for the patina to set on the 6AS7 SET top plate. But I just placed the copper on the chassis and it looks great!

Regardless of how much planning you do and how many test runs you accomplish, sometimes things simply don’t go as planned.

With the return of some more normal weather here I got the chance to work on the SET chassis today. Specifically I got the bare copper plates chemically treated for the patina for which I was looking. They look good. Or, more accurately, they look just the way I imagined when I first thought of doing this. I’m very happy with the results.

So I’ve been playing with the copper tarnish/patina process and I think I’ve got it figured out. After doing lots of small parts with various approaches I’ve learned enough to start the amp pieces. Among the things I’ve learned is that the washing process both before immersion in the chemical bath and after tarnishing while washing off the chemicals is very important. I’ve also learned that an even buff with a steel wool is better than taking the copper to a high gloss shine. And finally, the initial tarnish is very fragile. After doing the bath and letting the piece dry, it really should be left sitting in the open air for between three and five days. After this, the oxide layer toughens up and it can be handled and clear coated.

As I mentioned back in June, I have been looking at different finishes for the copper portions of my 6AS7 SET amp. At that time I had mentioned that I was interested in a “patina” type finish for the copper. I learned that to many people copper patina means green tones, blue corrosion, and wild colors. I was looking for something more like a tarnished penny look. Something that would make the unit look more like an older piece of equipment. Unfortunately this was to be more involved than I first imagined.

“Peck”. This is a term with which I don’t expect most tube amp builders to be highly familiar. However, it is a term that is exceedingly important to my work this morning on the 6AS7 SET amplifier. Let me explain.

I’m now just shy of ten weeks into my new routine and there are a lot of projects vying for my time and attention. This situation has made it difficult to make serious progress on my 6AS7 SET project.

I have been doing internal layout work and making some design decisions concerning the new SET amplifier. I have also been looking at different materials and I decided that I wanted to make the top plate holding the transformers and tubes of brushed copper. While this is an simple decision to make at this point, it raises the issue of what wood to choose for the chassis frame.