Point Contact Transistor Connect Collector Load Output Signal
# Connect a Load in the Collector Circuit: Current Alone Is Not Yet a Signal
Step 19 put the collector into reverse bias and gave it a steady current to carry, but a current flowing through a wire produces nothing an outside circuit can observe unless something converts a change in that current into a change something can actually measure. Step 20 is the step that performs that conversion. A resistor placed in series with the collector turns every fluctuation in collector current into a corresponding fluctuation in voltage across itself, and that voltage swing — not the current directly — is the output signal every amplifier built on this device actually delivers. Without this load, the device could be injecting, diffusing, and collecting holes exactly as every earlier step intended, and nothing outside the cartridge would show the slightest sign of it.
The load's size is bounded from both sides, and both failures trace back to a step already finished. A load too small barely converts a current change into any voltage worth measuring, leaving the collector's high-impedance advantage from Step 17 almost entirely unexploited — the whole point of a reverse-biased collector operating at high impedance was to turn a modest current into a large voltage, and a load far smaller than that impedance throws most of that advantage away. A load too large drops so much steady voltage under the quiescent current Step 19 established that the collector's own reverse bias can no longer be sustained at the margin that step worked to set below breakdown — the load competes with the supply for the same voltage budget, and a load sized without reference to Step 19's chosen operating point can quietly erode the very bias condition that step verified.
This step changes nothing about the device and changes everything about what can be observed from outside it. No voltage applied to the device itself is any different after this step than before it; the emitter is still forward-biased exactly as Step 18 set it, and the collector is still reverse-biased exactly as Step 19 set it. What this step adds sits entirely outside the cartridge, in the external circuit, and its only function is translation — turning an internal current, which Step 19 already established flows in response to Step 18's injection, into an external voltage that a later measurement can actually read.
| Step | Process operation | Input | Output | Specification | Constraint |
|---|---|---|---|---|---|
| 20.1 | Determine the quiescent collector current and voltage established by Steps 18 and 19 | Confirmed bias conditions from Step 18.5 and Step 19.5 | Known quiescent operating point | Current and voltage values recorded, not estimated, from the already-verified bias condition | Choosing a load value without the actual quiescent point risks a load sized for a different operating condition than the device actually has |
| 20.2 | Select a load value that converts a meaningful fraction of the collector's high incremental impedance into voltage swing | Quiescent operating point from 20.1, collector impedance implied by Step 17's topology | Target load value | Load comparable to or larger than the emitter-side impedance, consistent with the power-gain mechanism from Step 17 | A load far smaller than the collector's own impedance wastes most of the impedance-mismatch advantage Step 17 depended on |
| 20.3 | Verify the load does not drop the collector voltage below Step 19's breakdown margin or reduce it toward the bias-collapse edge | Target load value from 20.2, quiescent point from 20.1 | Load-line-verified value | Resulting operating point sits between both edges identified in the load-line diagram, with margin on each side | A load that satisfies 20.2 alone can still push the operating point against either edge once its steady voltage drop is accounted for |
| 20.4 | Connect the load into the collector circuit | Verified load value from 20.3 | Load connected, collector circuit complete | Measured quiescent voltage and current consistent with the values predicted in 20.1 through 20.3 | A measured mismatch after connection indicates a load, supply, or wiring error that the calculation alone could not catch |
| 20.5 | Confirm the device still meets its Step 18 and Step 19 bias conditions with the load connected | Connected circuit from 20.4 | Bias-confirmed, loaded circuit | Emitter and collector bias conditions unchanged, within tolerance, from their values before this step | A load that silently shifts the bias conditions undoes the verification both earlier steps already completed |
| 20.6 | Record the load value, resulting operating point, and verification results against the device's complete record | Confirmed circuit from 20.5 | Documented collector-load configuration | Load value and operating point recorded against every provenance record since Step 2.6 | Without this record, a later signal measurement cannot be tied to a specific, confirmed load condition |
Step 20 does not make the device do anything new; it makes the device's existing behavior legible to anything outside it for the first time. Every step from Step 1 through Step 19 built, verified, or biased the device itself, and every one of those steps could, in principle, be checked by measuring something about the germanium or the applied voltages directly. This step adds nothing to the device and everything to what comes next — because without a load converting current changes into voltage changes, Step 21's signal and Step 22's measurement would have nothing external to act on, no matter how correctly every earlier step was performed.