Rap 'n Tap
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From: W4HAY Frank
Time: 6:02:53 PM
Remote Name: 188.8.131.52
For the person that asked about grid-leak detectors: (sorry I couldn't reply before archive)
I've had very good luck using a 1T4 in the classic pentode GL and regen configurations. The grid leak is 2.2 Meg & 220 pF in parallel. B+ is 45 volts from five 9V batteries, Screen voltage is taken from a 50 K pot. As you increase the screen voltage from zero you will hear the gain increase rapidly and then stabilize. This is the optimum setting. If you monitor the plate current you will see it begin a very rapid increase after the optimum gain setting which just wastes batteries. Pin 1 is the supressor grid and one side of the filament and should be tied to ground. Try reversing the A battery polarity for optimum detection (gain vs. distortion) one way works best for strong signals, the other for weak ones. Above 3 MHz the GL capacitor should be reduced to 100 pF. The circuit is put together on a radio shack #276-150 board which can be just put in place of the "rock" on any Xtal set.