The dual transistors and their connections suggest a class-B 4th stage ( 8 ), although it could be 2 out-of-phase class-As to cancel symmetric distortion or something there's a couple trimpots which seem to set the DC bias for each transistor independently. After that, my guesses get far more vague as my lack of knowledge really shows itself here. The DC bias, feedback, and load inductor is the same as the previous two stages. Input of the 3rd stage doesn't have any elaborate matching network, just a variable cap on the gate. 2nd stage (5) has a different transistor (AR156) but otherwise similar has the same feedback structure, variable drain cap, and dual-inductor load. 1st stage output is AC-coupled to some kind of matching network. The cap at the input to the large inductor provides some local decoupling. The large inductor is probably for low frequencies (it's supposed to operate over a really wide frequency range.1.4mH = +j88 ohms 10kHz) and the small inductor (the toroid) is probably for high frequencies where the SRF of the large inductor makes it no longer inductive. The drain is loaded down with a variable cap, and fed with bias from a series large inductor (marked 1.4mH) and a small inductor (the toroid) in series. 1st stage has some bias fed from a trimpot, and some feedback through a (large brown) resistor and a messily-wound inductor to the gate. For the RF parts, a schematic should make it easier: (For what it's worth, I have no idea if the transistors are bipolars or FETs, but I've drawn them as FETs just because) RF input enters through coax on right (3) goes through a DC-blocking cap then back-to-back diodes for limiting, and gets AC-coupled to the 1st stage (4), with an AR153 transistor. There's also what looks like a thermal cutoff switch (2) to kill the power if that giant heatsink gets too hot. There seem to be a few linear regulators at the top-right edge (1) for biasing, and maybe for the actual DC collector/drain power, but that seems less likely. RF amps are not something I have a lot of experience with though, so this interpretation is going to be shaky in a lot of places, but here goes. Here's the interesting part though, the RF board! A closer look, you say? Luckily, since it's just a 2-layer board with easily-visible through-hole components, it's not that hard to figure out how everything's connected (especially as it's all 80% ground plane, as I'd expect from anything reasonably high-frequency). I didn't dig down to the level of the power supply, as that would've been some pretty involved disassembly on a piece of equipment I don't own, and the power supply is almost guaranteed to be boring - just a transformer, bridge rectifier, and some capacitors. The entire thing is pretty much one giant heatsink, with an RF board on top, and the power supply underneath. It died at work driving some badly mismatched loads, from what I understand, but from the lack of smoke, obvious burned bits inside, etc. I have not confirmed if other AMP Research models’ of steps will work with this conversion kit so it is strongly suggested to use the model mentioned above.This is a 50W RF amplifier, which claims to work from 10 kHz - 220 Mhz. Note: Regular Cab Rams require a large hole or slot to be drilled for the mounting insert, otherwise installation is identical to extended cabs and is not difficult for either model. This conversion kit uses AMP Research Model# 75101-01A, which is originally for ‘03-/3500 Quad Cabs, and converts it to fit ’94-02 Dodge Ram 2500/3500 trucks.
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