OC44 vs AC107
What's the difference?
The main difference in price is the OC44 was used in the original Dallas Rangemaster units and the AC107 was not.
This creates a higher demand for the OC44. These old germanium transistors becoming more rare, the prices for the "mojo" parts are rapidly increasing. This doesn't mean one is necessarily better than the other, the price difference merely reflects the scarcity of one over the other. Since the AC107 wasn't used in most classic germanium fuzz & boost pedals of the 1960's, they aren't as in high of demand as the OC44 or OC75. So if you're looking for the most authentic parts, the prices reflect that.
Both transistors were made by the major transistor manufacturers in the early 1960's like Philips, Mullard & Valvo.
The original Dallas Rangemaster unit shipped with either an OC44 or OC71 black glass germanium transistor. These were not an option that a customer could pick. Dallas Arbiter bought the best performing yet cheapest transistors they could get at the time, which happened to be the OC44 & OC71. These transistors typically measured in the gain range and leakage that is ideal for the Rangemaster circuit. But were mainly designed as an oscillator and mixer use transistor.
The AC107 was actually a more expensive transistor at that time, as it was a germanium alloy low noise AF pre-amplifier. Making it a great alternative in the Rangemaster circuit as it is a very rudimentary pre-amp. I have become very fond of the AC107 and use this for the majority of my Treble Boosters for its consistency and fantastic tone.
The difference between the two sonically is pretty subtle. The best way to describe it is - they are both different shades of the same color.....if that makes sense. It’s tough to describe, but that is the best analogy.
Below are a few demo videos that do a good job of showing the tonal characteristics of each transistor
OC44 Treble Booster
AC107 Treble Booster