Output audio transistors
ex : AC128 (Fuzz Face, 1966-69)
These transistors were at first designed to drive the loudspeakers of radios and consumer audio products. They are distinct from other families by their dissipable power and their maximum collector current.
In 1967, some models have been known as bringing a so called “creamy” sound texture to Fuzzboxes. Therefore, they gained a reputation that made this family of components enter the guitar effects culture.
Average characteristics of the AC128 family
Maximum collector-emitter voltage: 12 to 20 V.
Power dissipation : 0.5 to 1.2 W (more than most of other small case transistors).
Maximum collector current : 0.5 to 1.5A (more than other small case transistors).
Gain : 80 to 250 (rarely more than 150).
Maximum frequency : 0.5 to 1.5 MHz (never higher).
Any germanium transistor inside these characteristics, and presenting a leakage current Iceo lower than 500μA should work well in a Fuzz. If well biased, the sound would be what “vintage” means : not shrill and responsive to the way of setting and playing the guitar.
From left to right : AC128 by Philips / Mullard ; AC128 by Tungsram ; GC301 (GDR) ; GT402b (USSR) ; SFT363 (Italia)
Underlined items have been used in historic pedals.
Items with number followed by an asterisk * are npn models.
European ACxxx family
AC128 … Original model, TO1 Philips / Mullard, often called “Red dot case”.
Initially used as a replacement piece for maintenance, it became a reference transistor around 1967. Well biased, it gives the creamy sound that made the Fuzz Face a myth.
AC141*, 142, 180, 181*, 188, 187*… (almost identical, by other manufacturers)
AC127*, AC176*… (npn versions of AC128, sometimes referred as “Blue dot”)
Less well known cousins :
AC124, 131, 138, 139,
AC184, 185*, AC193, 194*
Other european models
SFT363 … Quasi equivalent to the AC128, diffused on the European market.
Used in the Italian versions of the Tone Bender Mk1.5, in 1967-75.
Sometimes found as a replacement in some vintage Fuzz Faces.
SFT 367/377*, 370, 387… Europeans cousins one should try.
ACY17, 18, 19, 20, 21, 33… Industrials models, generaly more reliable…
NKT211, 223, 271… Brits to rediscover, if any …
Eastern Europe models (Hungary, ex-GDR or ex-USSR)
Unknown or stupidly disparaged before the 1990s, they are far from being dull.
By order of interest :
A little forgotten or underestimated, so not common, alas.
It is the East German AC128, with a credible wet sound, albeit a bit dark.
Works well in Fuzz Faces in the position of second transistor (after AC125 or 128 as T1).
AC128 by Tungsram…
Official clone made in Hungary. Not ridiculous compared to the original Philips / Mullard.
It does not really give the wet sound of Mullard AC128s, but its medium tone is enjoying.
Still fairly easy to find.
Russians items, close to AC153, giving a vintage fuzz that crunches just what it takes.
Codes have numerous suffixes, without great influence on their sound in fuzzboxes.
Not hard to find. Huge bomb-shaped case, which makes its vintage visual effect!
GC511, 521* by Tesla…
Czechs items that give a rather rough sounding fuzz, too sour for my taste.
America and Japan
Some classic models, often mentioned, but there should be surely many others …
(I have not done wide research on this subject, because already well occupied by Europe).
I apologize to the visitors who will be frustrated by this lack of material !
I recall that apart from certain mythical or magical components, it is the technological family of transistors that is significant, rather than the particular model …
2N508, 2N527… Commonly cited antique American models.
2SB324, 383, 405… Japanese equivalent or close to the AC128.
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