Point Contact Transistor Measure Response Verify Power Gain
# Measure the Response Across the Collector Load: The Question Step 1 Opened Finally Gets Answered
Step 1 opened this entire sequence with a warning: rectifier-grade purity alone does not guarantee transistor action. Twenty-one steps have since selected a material, shaped two faces, conditioned a surface, built and formed two point contacts, wired a circuit, and biased it into operation — and not one of those steps, individually, proved that any of it actually works as an amplifier. Step 22 is where that proof either arrives or doesn't. A measurement taken across the load Step 20 connected, compared against the signal Step 21 applied, is the only operation in this entire sequence whose job is to answer the question Step 1 asked at the very beginning.
Amplification and power gain are not the same claim, and this step has to check both. Voltage amplification is the easier of the two to see: the signal Step 21 applied across the low-impedance emitter-base loop was small, and the voltage swing Step 20's load now produces across the high-impedance collector loop should be larger, simply because the same current, encountering a higher impedance, produces a larger voltage there than it did at the input. Power gain is the harder and more important claim, because it is the one Step 17 staked the entire circuit topology on — a point-contact device that injects holes with an efficiency below one does not multiply current, so the only way it can still deliver more power at the output than it consumes at the input is through exactly the impedance mismatch Step 17 described. This step has to compute both the input power the signal source delivers and the output power the load dissipates, and confirm the ratio actually exceeds one, not merely confirm that a voltage appeared.
A measurement taken here cannot, by itself, tell anyone which earlier step is responsible for a disappointing result. If the measured gain falls short, the fault could sit with a diffusion length too close to the point spacing, a forming pulse that left the alloy region under- or over-developed, a bias point that drifted outside its linear region, a load sized without enough margin, or a signal that clipped on one of its swings — and this step's own reading, the voltage and current it captured across the load, looks the same regardless of which earlier decision actually failed. This is not a weakness unique to this step; it is the cost of every verification this series performed along the way being a check on one component or one condition in isolation. Only this step checks the whole chain at once, which is exactly why it cannot, on its own, say where a broken link sits.
| Step | Process operation | Input | Output | Specification | Constraint |
|---|---|---|---|---|---|
| 22.1 | Measure the output voltage swing across the collector load in response to the applied signal | Signal applied in Step 21, load connected in Step 20 | Measured output voltage swing | Swing measured over the same time base as the input signal, isolated from the steady bias component | Measuring total voltage without separating the signal-driven swing from the fixed bias component overstates or understates the actual amplification |
| 22.2 | Compute voltage amplification as the ratio of output swing to input signal amplitude | Output swing from 22.1, input amplitude from Step 21.1 | Measured voltage amplification | Ratio computed against the same reference node established in Step 17 for both quantities | Comparing voltages measured against different references produces a ratio that does not correspond to any real circuit quantity |
| 22.3 | Measure the input power the signal source delivers into the emitter-base loop | Signal from Step 21, emitter-base loop impedance | Measured input power | Power computed from the actual signal voltage and current at the emitter-base loop, not estimated from voltage alone | Input power calculated from voltage alone, ignoring the loop's actual impedance, can misstate the true power delivered |
| 22.4 | Measure the output power the load dissipates in response to the collector current | Output voltage swing from 22.1, collector load from Step 20 | Measured output power | Power computed from the actual voltage and current across the load during the signal's full swing | Output power calculated only at the peak of the swing, rather than across its full range, can overstate the usable power delivered |
| 22.5 | Compute power gain as the ratio of output power to input power and confirm it exceeds one | Input power from 22.3, output power from 22.4 | Verified power gain | Ratio greater than one, confirming the impedance-mismatch mechanism from Step 17 actually delivered net power gain | A ratio at or below one means the device amplifies voltage, if it does at all, without delivering the power gain the circuit topology was built to provide |
| 22.6 | Record voltage amplification, power gain, and both measured powers against the device's complete record | Verified gain from 22.5 | Documented, verified amplifier | Both ratios and underlying measurements recorded against every provenance record since Step 2.6 | Without this record, a successful or failed result cannot be distinguished from a measurement error, and cannot be compared against a later device built the same way |
Step 22 does not add anything to the device; it is the only step in this entire sequence whose purpose is to find out whether everything else was worth doing. Every material choice since Step 1, every dimension since Step 2, every bias and signal condition since Step 17, was made in service of a claim this step either confirms or fails to confirm: that a reverse-biased collector operating at high impedance can turn a small signal injected at a low-impedance, forward-biased emitter into more power than it took to produce it. This is the step that closes the question Step 1 opened on its very first line, and it closes the original, mandatory construction and operation of this device — everything documented after this point in the historical record describes alternative ways to build the point contacts themselves, not a continuation of the procedure this sequence has followed from Step 1 through here.