Cristal Set detectors

OK, usually we use a single crystal or diode. A voltage doubliing circuit gives more volume, but if we can also trick the circuit into biasing the diodes, we can boost sensitivity as well. Here's how *I* do it:

• D1,2 are 1n34/1n34A. IF you have a diode testing scale on your meter, try to select 2 diodes that give VERY close readings- identical is tooo much to ask for, but close is possible.

• C1,2 are .001 to .002 uFd. IF you have a capacity meter, try to match a pair of caps.

• C3 is .01 uFd. LOW LOSS is critical for all 3 capacitors, a good ceramic or plastic is fine, using old salvaged waxed paper capacitors is a no-no. DO NOT even CONSIDER electrolytic capacitors of ANY sort in this circuit!

• R1,2 are usually 47-68K ohms; possibly as high as 100k. I generally go with 47k-56k. MATCHING resistances with a meter REALLY helps.

• VR1 is typically a 1K ohm trimpot buried in the guts of the set, or about 1-2% of the TOTAL of R1+R2. If you select R1,2 with a meter to insure a close match, this can be smaller and allow easier adjustment for perfect balance. Adjust VR1 tor best performance on weak signals.

This is good for AT LEAST 6db of volume, and when you set it up right is at least SOMEWHAT more sensitive to weak signals.

Here's the deal: we start off with all capacitors discharged, 0 volts. We toss in the first RF. D1 conducts, piling electrons onto the diode side of C3. End of cycle, RF is at 0 volts, lots of electrons trapped on C3. Hmmm... OK, here comes negative half of the cycle. Electrons are pushed through D2- but with the extra negative charge on C3, that starts much sooner. End of cycle, C3 has a slight POSITIVE charge on it. Here comes positive haldf of RF cycle, and - it starts conducting ssoner.

This cannot boost initial activation, but if there is ANY current flowing through the diodes, it self biases and becomes more sensitive- and this in thrn means the diodes are working further up their conductivity curves, where they will deliver MORE OUTPUT. and as this is being doubled anyway-wheee!!!