I've installed an RFX-75 (Rev. 2) on an old, single-finaled, SS-3900 and am DELIGHTED with the results.
In the past, if I wanted slightly more power out of a radio, (without an outboard/external linear amplifier) my only alternative was to install dual finals. This was a time consuming process, and has become increasingly more expensive to find a beta matched pair of 1969's, not to mention all the associated hardware & components, plus the heatsink needed for a Galaxy or Ranger chassis radio. All that to hit anywhere from 35 - 55 watts of output power on SSB. Not to mention that on the AM only Cobra and Uniden chassis rigs, (like Cobra 25's/29's, Uniden 68's/76's) the only 3 options I had were: A - a single 1969/2312 final upgrade or B - the IRF520 or 2030 MOSFET upgrade, which (again) would roughly only yield an approx. 3 - 5 dB gain in measured output power. Or C - an internal 'Stinger Board' that which would require me to remove the internal speaker in order to mount the Stinger, thus requiring me use an external speaker.
So, I picked up an RFX-75 Rev. 2 (enhanced for better SSB operation with improved biasing) PLUS an RFX-150 over the Christmas holiday season, brought them home, and then had to decide which two rigs to test them in. Believe it or not, (mostly because "they" said it couldn't be done), I mounted the RFX-150 on my Realistic TRC-465 and am COMPLETELY ENAMORED with it. It's now a whole new radio, AND very stealthy. Also, the 2166 driver with the 1969 final in the TRC-465 offers more than enough drive for the RFX-150.
I was tempted to install the RFX-75 in the RatShack, but I saved it (the 75) for my last remaining single-finaled Galaxy chassis: the old school SS-3900.
My SS-3900 had already been modded to the hilt with all the typical Galaxy/Ranger EPT board mods and I was already considering adding a 2nd final, heatsink, & associated components to up the power output. However, for much less time, money, parts, and PITA Factor, I was able to install the RFX-75 much easier to this full sized chassis radio than it was to install the RFX-150 on the TRC-465.
Results with the RFX-75 on a single finaled SS-3900 are as follows (these are conservative measurements, as the RFX-75 instructions indicate that the unit is capable of a 15 watt dead key, but I turned mine down to 10 and that really helps prevent heat buildup, thermal instability/degradation, etc.):
AM Deadkey: 10 watts; AM Swing watts: 22 watts
FM Deadkey: 10 watts; FM watts: 10 watts
CW Keydown: 10 watts; CW watts: 10 watts
AM Peak watts, 100% modulation, 1000Hz tone: 65 watts
SSB PEP Output: 65 watts PEP
Unit is capable of much more than this. However, as I had mentioned, I'm running it a little 'light' which seems to aid in keeping it cool. I can ragchew all I want to and it won't get hot to the touch, merely warm. Cooler actually than my RCI-2950DX heatsink, and the 2950 is only doing 35W SSB PEP, whereas the SS-3900 with the RFX-75 is at 65W SSB PEP.
I'd have to say that this thing (the RFX-75) is truly a GEM, and solves the heat problems and/or SSB issues previously associated with running a Stinger Board internally.
Now, to those of you who would opine to use a tiny KLM amp externally instead, I say this: for AM ONLY use, this might be fine. However, keep in mind that more often than not, you will be RF switching, and/or, capacitor delaying (i.e.: on SSB) the keying of your external amplifier, which does NOT lend itself well to either SSB or high speed CW usage. Since you're pulling 8V directly off of the PTT of the transceiver to key/unkey the RFX-75, it really lends itself well to SSB and high speed CW ops IMHO. True however, that you can develop more power with an external amp, the fuse(s) are easier to get to for servicing, and/or your amp might even offer an external receive preamp, things 'lacking' in the RFX-75. In fact, in the unlikely event you blow the fuse in the RFX-75, something I in fact DID DO upon initial key up, (as I had the output power of the SS-3900 turned up way too high initially and developed in excess of 100W output on AM momentarily before the fuse blew), you will be required to take the cover off of your radio to regain access to the RFX-75 fuse assembly.
Now, the RFX-150 on the other hand, is a whole different animal. Because I was mounting it on a small radio, I lost my PA and External Speaker jacks, as the mounting plate for the RFX-150 is now covering them over. I installed my RFX-150 in such a way as the rig gets its power directly from the RFX-150, and so I only have to use the one set of heavy power cables coming from the 150 to power up the whole she-bang. I also mounted a subminiature SPST switch on the 8V (blue) wire energizing the 150 on the side of the TRC-465 just in front of the (already) side mounted mike jack. This permits running barefoot, or energizing the RFX-150 for high powered operations.
RFX-150 results on a tuned TRC-465 are as follows:
AM DK: 30 watts; AM Swing Watts: 50 watts.
AM Peak Watts, 100% modulation, 1000Hz tone: 130 watts.
SSB PEP Output: 135W PEP
On both radios, AMC and ALC circuits were left in tact.
Also of note, on both radios (the way I installed the devices), the RFX units are always 'ON', as they are always receiving 13.8 VDC down the line, whether the radios are on or off. This is a consideration you must take into account IF you install them directly off of your batteries. In this instance, you might want to place a heavy duty switch in your 13.8 VDC line. In my situation, the power source in the mobile (RFX-150 on the TRC-465) is only energized when the ignition is on.... so no problem with draining the car battery. In the shack, the SS-3900 is connected to a power supply that runs off of the AC mains that I switch OFF when not in use, thus unpowering the 13V supply to the RFX-75.
My next test will probably be to put an RFX-75 on a Cobra 29 or 25, and you can be sure that I'll also adjust the output of the Cobra/input of the RFX such that the RFX-75 does NOT exceed 75 PEAK watts of output power when modulated. This should provide a decent amount of longevity without any thermal issues. Quite frankly, with RF being what it is, the receiving station will see absolutely NO DIFFERENCE on their S meter if you're running 60 watts, versus 90 watts of output power. Not only that, but you exceed 75 watts on an RFX-75 with a 12-13VDC power source, and you'll blow that fuse in it eventually (like I did on initial transmit test.)
As far as SSB operations are concerned, I never had a 1st generation RFX unit to put on the scope (Wawasee Catalyzer), but I DID run SSB tests on BOTH the RFX-75 Rev. 2 and the RFX-150 and can attest to the fact that IF you moderate the SSB output power they provide a nice clean waveform. However, if you run them maxed out, they WILL FLAT TOP on you, so be warned in advance. I even heard rumors of square wave patterns, and/or insufficient SSB drive issues on the first gen 75's, but have no first hand experience with same.
I'd conclude that the RFX-150 is perhaps best geared towards the DUAL-FINAL and/or SSB user, whereas the RFX-75 is maybe designed for the single final radio user, chiefly because IT becomes THE final amplification stage(s) of your radio. Also, to address a question posted earlier in the thread about "WHAT IF" my radio only delivers 500mW in my driver, I'd say that the RFX-75 would be your go-to choice in this instance, and certainly NOT the RFX-150.
For ME, the 'toughest' part of the installs was drilling holes in perfectly good radios, ESPECIALLY the 3/8" (minimum) you'll need to route all the wires of the RFX-75. Likewise, the mount of the RFX-150 on a small chassis offers its own set of complex issues, so be warned.
Good luck & happy experimenting. Looking fwd. to learning about additional experiences and outcomes with these two nifty enhancements.