I feel this is a much better alternative than the Ramsey LPA-1 because it provides much lower harmonic output and it is relitivly bullet proof to antenna mismatches which has been known to destroy LPA-1s without the slightest warning.
The PCB board is a single sided copper board etched or grinded out to the shown layout. The board size is 3 3/8" x 1 3/8" but anything close that can accomidate the parts without any lengthing of the lead lengths is fine.
I recommend that if you don't have a good way to make the PCB that you buy the Radio Shack PCB Etching Kit, this kit works very well for this type of application. We've used laser printer iron ons for this board, but we've found that electrical tape or the resist pens work fine.
In the first stage the resistor R1 (1.5K) gives Q1 (mpf-901 or mrf-901) and the Ramsey transmitter a nice stable input/output load to look at that should smooth out missmatches between the transmitter and the amp (note that this type of matching is only workable at flea power levels.. < 50mw.) R2 (20K) provides the bias voltage making the amp class-A. Current is fed to the stage through R3 (300ohms) with a ferrite bead on the power side to help keep RF out of the power grid. An inductor of 1uh or better can be substituted if a ferrite bead cannot be found (use only small resistor type inductors, not giant monsters from Radio Shack). The first stage is isolated from the interstage maching circuit by C12 (.001).
Intra-stage matching is done by C1, C2, and L1. This network trys to match the output impeadance of the first stage with the input impeadance of the second stage. It also provides a little bit of filtering. It should be noted here that the power output of the first stage affects it's output impeadance which is effected by the input power level. Any change in power outputs of the transmitter (most likly from frequency or power supply change) will require re-tuning of this amplifier.
The second amplifier is running Class-C pushing it's output into the output matching circuit made up of C3,C4 and L2. The output is fairly clean and can drive an antenna or another stage.
For tune up you should simply tune C1, C2, C3, C4 and L1 for maximum
output. This amplifier doesn't like to ocsillate, but this is always
a possiblility. You can check for oscillation by tuning a FM radio
up and down the FM radio band, if you hear multiple images of your
broadcast your amplifier is in oscillation (not good).
I would get rid of C12, it is not necessary since C2 blocks the DC between stages. I would move C1 to the other side of C3, this allows C2 to be adjusted without effecting the C1/L1 low pass filter. I would add another 5-50pf cap from the input side of L2 to ground, thus adding an extra element and more flexibility to the output/matching filter (I would and have done this addition on every amp that I have built, cannout get -50db down on harmonics without it.)
The modifications listed above can easly be made to the existing circuit board if done during the assembly stage. Basically you would shift Q1 and its associated parts one pad to the right on the circuit board (since C12 is no longer necessary), and add a .001uf cap between the first pad and the base of Q1 pad. C1 can easly be moved to the pad on the output side of C2. And another 5-50pf variable cap fits nicely on the input side of L2.
L6 mostlikly can be optimized, but is most likely not that critical to the overall performace of the amp.
R1 1.5K ohms R2 20K ohms R3 300 ohms
C1, C2, C3, C4, (C14) ~5-50pf C12,(C13) .001uh C5, C7, C9 .01uf C6, C8, C10 .1uf C11 10uf
L1 .2uh adjustable digikey...
L2 .2uh fixed coil...
L3,L4,L6 10uh Moulded Inductor
L5 3 turns of #22 enamal wire through Ferrite
Bead.
Q1 mpf901 -or- mrf901 Q2 2sc1970