High Frequency Transistors
ex : OC44 (Rangemaster, 1966)
High frequency germanium transistors have appeared as a second generation. Their elaborate technology made it possible to obtain a consequent gain even at radio frequencies : 30MHz, then 100MHz or more.
More expensive, and fragile at the beginnings, they have not been much used by pedal manufacturers, before all concerned by economy and robustness.
The OC44 was however exploited by Arbiter in the first Treble Booster, the Rangemaster, where its gain and bandwidth yet modest worked perfectly.
With the contemporary recoil, we rediscover the quality of these transistors, the fineness of their sonic grain, and their real interest in designing modern boosters and fuzz …
OC44 and OC 45 Mullard / Philips (Black Glass) ; AF124 ; ΓT313A, ΓT320Б, Π416Б (USSR).
Average HF Family Characteristics
Collector-emitter voltage: 10 to 20 V.
Power dissipation: 20 to 150mW (low).
Maximum collector current : 10 to 50mA (fragile!).
Gain Hfe: 50 to 200 (one should prefer 100 or more).
Maximum frequency: 50 to 450 MHz (much higher than audio models).
Transistors within these range of characteristics are able to work well in treble boosters, or in modern fuzz generating a lot of harmonics. As they are rather fragile, One should use models with maximum voltage 10V or more, and whose collector current exceeds 50mA.
Underlined items have been used in historic pedals.
items followed by an asterisk * are npn models.
European models :
First generation HF transistors, still in Black Glass housing.
Their maximum frequency remains limited, but they are not much leaky.
They equipped the historic Rangemasters. Still topical in building clones.
Avoid false maneuvers because they only supports 10mA collector current !
AF114, 115, 116, 117, 118…
First European transistors for FM radio.
Deprecated in pedals, because very sensitive to static electricity.
SFT115 à 120, SFT316…
Other radio-frequency models… SFT 316 has low leakage current.
AF124, 125, 126, 127, 128…
Second generation of radiofrequency transistors. More efficient and reliable.
Widely used around 1990/2000 in Fuzz clones and neo-vintage boosters.
Russian models :
Quality models, bizarrely relatively few quoted on the forums.
They benefit from the technological longevity of germanium in the USSR, which has made it possible to improve the reliability and to envisage a good reproducibility in production.
Moderate gain. (≤80)
ГT313A, П416A… Very reliable, but gain ≤ 60. One have better to look for a higher gain.
ГT308Б, ГT309A ou B… idem, in subminiature metal case.
ГT313Б, 320Б… Reliable and musical, the gain ≤ 80 is just sufficient in many cases.
Medium gain. (60-120)
Accurate and reliable, without any particular coloring effect on sound.
Work good in high fidelity preamps or boosters.
A welcome high-midrange hue when used in treble boosters or vintage fuzz.
Clear tone, with slight dynamic compression. Good musicality in boosters.
Good NPN radio frequency models. Rare.
Sorry, I have not done any research on American or Japanese transistors.
For more informations…