IMO, there is considerable confusion regarding the 2SC5200 bipolar transistor.
Please look at the data sheet for this device and in the maximum ratings, Vebo = 5v max. This is not Vbe the forward base/emitter voltage, but rather Vebo which is the maximum reverse emitter/base voltage. What this means is that the emitter/base junction, if subjected to a reverse voltage of no more than 5v, will be guaranteed not to avalanche. This has nothing to do with the normal operating forward voltage of the base/emitter junction. There is no way that the forward voltage of this device or any NPN power device or small signal device could reach 5v without complete destruction of the junction.
In the electrical characteristics for this device, we see the maximum operating Vbe at 7 amp collector current is 1.5v with a typical value of 1v.
Now, as to the operation of the circuit, there are only three modes that the 2SC5200 can be operating in not counting on/off switching. These would be class A, some form of B, or C.
In class A, the base is biased in such a manner that the dc quiescent point would be positioned at the midpoint in the collector load line. This mode normally allows for symmetrical clipping of the loaded collector.
In class B and all it's variations, the base bias is reduced so the device normally operates as a unipolar device regarding the AC signal. This type of operation is usually seen in totem pole style power output stages.
Class C operates with zero or negative base bias and again in a unipolar mode.
The Stalker circuit with the 2SC5200 base shunt and series resistors is the absolute worst design possible for hard switching of the device IMO. Therefore, I agree with Verpies that more than likely the device is meant to be biased in either class A or one of the B modes. If this is the case, I can see why there would be difficulty is achieving consistent results because of the base biasing scheme used. The large signal beta or HFE of these devices will vary across a lot such that with no emitter resistive feedback network, the base resistors will have to be experimentally determined and selected for each device used. Again, a poor design because this gain will vary with temperature which will be like hitting a moving target with the present base biasing scheme!
Evidence of this device operating in particularly class A would be the requirement of a large heatsink perhaps with cooling. It could be operating in class B with less bias which would lower the device dissipation and therefore the cooling requirements.
Therefore IMO, it would be most important to determine the operation of the overall circuit and how it would achieve gain.
Regards, Pm
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