Made in USA
It is my goal to use as many American sourced parts as possible, but with that being said, I won't use inferior products just because they are American made.
My typical hierarchy is this:
How does it sound?
Where is it made?
Cost is a consideration, but not for me. I let the end user decide that based on how I price my amps. I have an opinion on what I think is the best in terms of the above 3 items, and my suggested builds are based on that. When cost enters the equation, there's also some consideration to be made if the extra money is worth it. My belief is if you are going to buy a custom built amplifier, you might as well get the best of the above 3, but I can't make that decision for you, only guide you on my experience. All the parts I offer in my builds will yield very good sounding and reliable amplifiers.
In terms of what affects tone, I would rate it something like this:
Speaker and speaker cabs
Resistors/layout and other misc stuff
So if you believe me on this, in terms of what I put into a particular design, the output transformer is high on the list. I have yet to be able to hear a difference in a power transformer but the design and specs of the power transformer will affect overall circuit response. I prefer certain suppliers because I can get the exact specs I want or more options. In terms of what I pay, they are all pretty close, so it comes down to what one fits the circuit design the best. In some cases there are multiple transformer options that will work and maybe a slightly cheaper option.
All the transformers, with the exception of Hammond, I use are US made. Hammonds are made in Canada and are good quality. In my opinion they aren't as good as Heyboer, Mercury Magnetics or Magnetic Components in terms of tone, but pretty close on some of their stuff. I'll also use Edcor and I like their power and isolation transformers but they have long lead times.
In most cases I have found Mercury Magnetics to be the best sounding transformers. They are the most expensive, very high quality, come with a tone guarantee and 10 year warranty, and they have them in stock or build them quick. I get them for very good prices which I pass on to the customer and often times they aren't much more than the competitors for me (and YOU!). They claim to source everything down to their materials in the US.
My lower cost option for most transformers is Hammond or Magnetic Components. This is simply due to what is readily available. I can (and will) use Heyboer if a customer requests them. I can also get anything custom made from Heyboer if I can't get it off-the-shelf.
As for vacuum tubes themselves, getting US made tubes is only available via NOS (new, old stock). I will sometimes offer an amp with a NOS tube(s), but all my designs use readily available, current production tubes. I prefer if a customer wants NOS tubes to purchase them themselves. I can provide the amplifier without tubes.
The current production tubes are either European (Russian) and Chinese. I don't like any of the Chinese tubes in terms of sonic quality and won't supply them. Most all brands are owned by the parent company, New Sensor, but all the different brands are a little different. The Tung-Sol and Mullard re-brands are among the best sounding, in my opinion. They aren't the same as the NOS Tung-Sol or Mullard, but they are very good. In terms of bang-for-the-buck, JJ and Electro-Harmonix are excellent.
Signal capacitors have less of a tonal impact in most cases, although certain caps can sound really bad. I choose to use two different brands as I've found them to sound the best: Sozo and Mallory M150 re-production (now made by Cornell Dubilier Electronics, Inc.). Sozo makes two different types of caps: Phillips mustard clones and Astron clones. They both sound really good, and both are a little different. Sozo's are handmade in the US. The CDE 150's are machine-made in Asia. The M150's and Sozo's are actually pretty close in tone. Both are smooth and articulate with distortion. The Sozo's add more character to the amp; the CDE's are more "plain" sounding.
Other capacitors used in the amp that are electrolytic have even less affect on the tone, but e-caps are items that can, and eventually will fail. I prefer good quality Sprague Atoms or F&T (made in Germany) but have had good luck with Illinois. Illinois are Asian made and a little less expensive. I can spec them if desired. I've also have good luck with JJ caps (made in Europe) and they are a little less costly than F&T, but they only make can caps.
In terms of resistors I use what I think is appropriate for sonic quality, noise reduction and power handling. I can use very expensive, and ultra-high quality Kiwame and Mills resistors, but I only spec them in my high end 18W builds. In most cases I use Vishay or Xicon. You may see an IRC in your amp - these are great resistors specifically designed for audio but production has ceased I still have a few in stock. I use a mix of carbon composition, carbon film, metal film, metal oxide and wirewound depending on the positions in the circuit and power requirement.
All cabinets I supply are made in the US. I have a few different suppliers, one of whom is a local guy who will do very nice hardwood work with locally sourced woods if you desire. Hardwood cabs cost more than pine or birch cabs. Like all my parts, I don't mark these up, only pass them along in my builds. You are welcome to work directly with the cab suppliers if you like, just be sure we get our mounting and clearance dimensions right!