Even though I had a good bit of loudspeaker building experience with my own / friends’ projects as well as my involvement with Fried, until I began building amplifiers, I didn’t understand the importance resistors play in the sonic presentation.
At one point, I had four amplifiers in front of me, three of which using the same circuitry, differing only only in their passive components, and two of which only in their resistors. The first was a classic Dynaco ST70 using the carbon composition resistors of the day. The second using carbon film resistors and modern capacitors, with the third identical apart from its metal film resistors. I built both of these amplifiers in the same time period. The fourth amplifier was a Dynaco ST80, produced in Japan, built to correct all the supposed flaws in the original; increased power supply capacity, Mullard long-tail pair (used by 99% of today’s push-pull tube amps and most of the Dynaco replacement / upgrade boards) driver stage, LED bias indicators, and (ironically) a triode / ultralinear switch.
The resistors themselves profoundly influenced the sound.
The original Dynaco had that amber colored, overly warm, lush sound normally equated with vintage gear. The same amplifier circuit with metal film resistors not only sounded like a modern amplifier with its clarity, neutrality, and openness, it possessed a level of both speed and liquidity most products with another zero or two in their price tags hope for.
Despite the marketing claims amplifier manufacturers have used over the past few decades about their innovations and ingenuity, when it comes to tube amplifiers, the circuits remain the same as those used in the 1950s. THE single most meaningful difference between a vintage and modern tube amplifier is the metal film resistors, and to a much lesser extent, capacitors.
The guitar industry knows this all too well. The demand for the vintage sound by the customers has led to both the much higher collectibility and pricing of the original amplifiers, the reintroduction of those same products, at a much higher price point to boot, and the tuners in every town folks bring their amps in to up their tone. Number one way to get that vintage tone, carbon composition resistors.
And if anyone cared...the Dynaco with the carbon film resistors sounded less than noteworthy, possessing neither the charm some treasure vintage products for, nor the modern sound that I prefer. The ST80 proved to me how the simplicity of the concertina phase splitter produces a special sound the vast majority of today’s push-pull tube amplifiers simply do not. With few exceptions, high-end audio amplifier designers have rejected this topology over the years using the argument of lacking the gain the long-tail pair produces. However, since many here like to quote Nelson Pass these days in regard to our components producing more gain than we can make use of, I’m now going to begin claiming this an advantage for the concertina. And for what it’s worth, though the sound of the ST80 fell far short of the original as all of these "improved designs" do in my experience, I did appreciate the triode switch even if it conflicts with Dynaco’s actual raison d’etre of ultralinear operation
