With a device as simple as the Gremlin, you’re pretty much relying on the quality of the tubes to deliver the best sound. You certainly won’t get that with bottom-dollar, poorly-matched, poorly-constructed, noisy, microphonic 12AU7s. In fact, I’d say there’s something rather elegant about a tube-based device that pretty much relies on the quality of the tubes themselves to deliver best performance. So it costs $120. You could cheap out on tubes and get $120 worth of sound, or spend $500 on tubes and end up with a unit that sounds like it cost $620 instead $120.
Let’s say I build a simple RCA 12AX7 phono preamp. I use inexpensive but well-matched components--film caps, resistors, a Hammond power transformer. About twenty parts in all! Cost about $200. What’s going to sound better, cheap Chinese tubes or Telefunkens? The answer seems obvious. Now let’s say I spend $1500 on a Hashimoto power transformer, teflon capacitors, Takman resistors, etc. Will it sound better? Maybe. But with cheap Chinese tubes, the preamp will still sound mediocre. So basically I’ve wasted $1300 on fancy passives by cheaping out on the one device that actually makes a significant difference--the 12AX7.
The same goes for the amps and preamps I actually do build. I can tell you that the tubes I recommend make a bigger difference in the value of those components than any amount of money I could charge for Duelund caps or amorphous-core output transformers. Cheap Chinese KT66s produce less power and more distortion than the more expensive Gold Lions.
Dennis Had doesn’t use fancy components in his Inspire amps. He uses good ones that do the job and don’t get in the way of the sound. It’s up to you to decide whether that amp sounds just okay or wonderful, depending on how much you’re willing to spend on the tubes.