so, i had this AM-1 board which has long since stripped of its parts for other projects, save for a few resistors and caps. ive tried getting the original design to work decent for a little bit and then stripped it all. this board has been put away wet more times than my prom date which is evident by how much rosin gunk has built up over the joints. it was a mess, 5 channels of my music in the x-band, distortion, drifting, all the stuff you DONT want the transmitter to do. so i stripped the board bare and started over. the final/modulator is more or less based off of the corsette which can be found at: freeradiotx.blogspot.com/
1st thing i built was the oscillator around a 1700 khz crystal and a 2n4401.
C6, C7 .01
jumper from emitter of Q6 to emitter of Q5 (i did this underneath the board)
now the fun part. the series modulator/final based around an LM386, TIP41, and NTE128 (bfy51 equiv.) the LM386 is mounted in an 8 pin socket which is hot glued to the top of the PCB along the edge where R4, C11, and C3's place was.
R2 jumper "hot" side to pin 6 of LM386
C1 560 ohm resistor
Q2 emitter pin jumpered to pin 7 of LM386
Q2 base pin jumpered to pin 3 of LM386
Q2 collector jumpered to pin 5 of LM386
R6 ground side of R6 jumpered to pins 2 and 4 of LM386
Q1 TIP41 (note the different pinout and HEATSINK!)
L1 220uh choke in series with a 22uh choke and 560ohm resistor in mounted in paralell.
R1, on the "cold" side, cut foil trace with razor and make that into an island, jumper this to ground underneath PCB. install .01 cap (103) between the R1 ground island and the other leg of it ugly soldered between the 220 uh choke and the 22uh/560 resitor.
R1, on the "hot" side of R1, put a 33k resistor between that and the side of
R10 connected to the base of Q3.
underneath the pcb solder in a 470 ohm resistor between the base foil trace and ground.
Q3 is an NTE128 or BFY51 (HEATSINK!)
C 13, C 14 1800 pf
L1 4.7uh (31 turns on t-50-2)
misc power supply love:
.01 (103) cap between hot lead and ground underneat the PCB
in the finals area, i originally tried to use a 2n7000. for you folk out there who like to split hairs on power output, you can use one of these without any gate voltage to speak of and it'll put out a nice crisp signal at around part15 levels. i tried applying around 1.5v to the gate through a 38k resistor and a 1k trimpot. the power was nice, audio good but the trimmer and FET got quite warm. im thinkin if i were to attempt that again, id use a 10k or better pot off of a 5-9 volt regulated source to keep currents in check. over 1.5 volts and you risk destroying the gate. FETs are all about biasing at the end of the day