8/18/2023 0 Comments Ac128 transistor![]() The BC147, 148 and 149 can be replaced with BC107, 108 and 109 respectively - even the lead configuration is the same. Of particular note is the Mullard "Lockfit" range. Some familiar but early silicon transistors are unavailable, and with the continuing encroachment of cheap, disposable (and as many would describe it, nasty) surface mounted technology, leaded transistors in general seem to be under threat. Not even silicon devices are safe from the dead hand of obsolescence. However the AF239S is a UHF device designed for use in TV UHF tuners and has a low gain (min hfe 10) compared with the AF11x types (min hfe 50) and my experience is that it won't work properly if at all in most radio circuits. ![]() Another point to watch is that equivalent books list the AF239S as a replacement for the AF11x range. Incidentally, alloy-drift transistors tend to be noisy at low frequencies and as such are not generally suitable for audio circuits. There is no listed equivalent to the AF118 and where replacement is needed for an old transistor TV, it may be necessary to re-jig the circuit to take a suitably rated silicon device. In practice, the AF125 can be used to replace AF114/115/116. ![]() ĚF118: High voltage (75v) video amplifier for transistor TVs.ĚF117: General purpose RF/IF amplifier in LW/MW/SW receivers.ĚF116: IF amplifier for 10.7MHz used in FM receivers.ĚF115: Mixer/oscillator in VHF/FM front ends.ĚF114: RF pre-amplifier in VHF/FM front ends.The old TO7 alloy-drift transistors were specified as follows: For this reason you cannot generally substitute a silicon transistor for a germanium device without modifying the biasing arrangements. The base-emitter voltage (Vbe) is also lower at 300mV compared with 600mV for silicon. It is also strongly dependant on collector current and ambient temperature. The gain (hfe) of germanium transistors is generally lower and far more variable than silicon devices. A thin smear of heatsink compound should be applied when mounting replacements. Take care when replacing AD161/162, not to damage any mica insulating washers as this size (SO55) is not readily available. Ptot for the AD149 and AD161 AD162 assume they are mounted on a suitable heatsink. If replacing /K types with their integral heatsink block, the faulty transistor can be pulled from the block and the replacement fitted in its place. Please bear in mind that output transistors must be mounted on a heatsink when run at or near their maximum dissipation. All these devices are packaged in metal TO1 cans. The pnp AC188 and npn AC187 are intended for use as a complementary pair in transformerless output stages. Low power AF amplifier transistors like the OC71 can be replaced with the economically priced AC125. Type AC127 is the npn complementary to the AC128. For instance the CV7003 is an OC44 in uniform.Īudio medium power types OC72 OC81D OC81 can be replaced with an AC128, a relatively high voltage, high current device. Military devices are generally marked with a "CV" (Common Valve) number rather than the civilian code. Many devices have a suffix letter after the number: A = low gain, B = mid gain, C = high gain.ĭevices with no suffix can have an hfe anywhere within the part's specification. This letter is usually a V, W, X or Y and can be ignored. Q = Radiation emitting device (e.g LED)Īny third letter indicates the device is primarily intended for professional and industrial use.P = Radiation sensitive device (e.g photo transistor).The second letter indicates the intended use: ĝ = other compound semiconductor material.The first letter identifies the semiconductor type: Basically, British and European transistors are issued with a unique combination of letters and numbers. So the ProElectron organisation developed a new system of coding semiconductor devices and the one in use today. However it was quickly realised that everything would end up as an OC something or other (likewise with diodes, which would all become OAxx) and could be confused with existing cold-cathode valve types. Once upon a time, long ago, British and European transistors were commonly coded as valves: 0 = no heater, C = triode. My Workshop Portable Radio Index Manufacturers Index Radiograms-Record Player Crystal Sets Links Component Data Getting Started For Sale and Wants EMail Radio Constructor Magazines Valve Radios Transistor Radios Military Radios
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