On the board that contains the "less used" controls, the ones underneath the hatch on the top. See here and look at photo 3, you can clearly see the coin cell there (soldered): www.ebay.com/itm/196421016962

That is correct for antennas that are resonant. When an antenna is not resonant (which is almost always the case for this transmitter in an aircraft having a trailing wire antenna), there can be a large component of current that does not take part in delivering actual radiated power ("out of phase" current, also called "bad SWR"). This is the part of the RF current that the built-in antenna tuner needs to cancel out. But the RF ammeter cannot distinguish between such resonant currents and "blind" currents, and will therefore show a large current going into the (non-resonant) antenna depending on the impedance of the antenna (which on it's turn is frequency dependent). Think of it as the power factor that applies to the AC grid. An inductive load (or capacitive load) will show a large current going in that does actually not dissipate any power in the load. That translates to a power factor of 0, and won't make your outside kWh meter move. A purely resistive load (like an incandescent light bulb) will exhibit a current going in that DOES deliver actual dissipated power, and the power company will charge you for that one. That is a power factor of 1. Anything in between (like an AC motor) will be a load that is partially resistive in combination with a partial inductive (or capacitive) load. It is the same for the antenna that forms the load for this transmitter, but then at a much higher frequencies than 60 Hz. But the concept remains the same.

Sure, you can order just the board, not a problem. See here for ordering info: www.pekorf.com/PeKoRadioOrder.html Scroll down a bit and order the RVB-MP1 by filling in the form. Cheers.

228 / 5,000 Yes, that's right, the manual explains it (you can download the SL20 manual from the web). It is one of those small jumpers encased in plastic, which they often used for computer hardware in the old days. If the jumper is removed, the power supply is "softer". All you have to do then is adjust them all for the exact same voltage (without load), and when putting them in parallel. Use the same DC wire length for all 3 power supplies. then the current will distribute nicely across the SL20 supplies. 73s.

As far as I know, RS had at least two 2-meter mobiles, the HTX212 and the HTX252. Here the HTX212: www.ebay.com/itm/126385988318 HTX252: kzbin.info/www/bejne/nWjFknmhpriMqqs Cheers.

@@LifeIsTooShortForQRP I don't remember those. I bought a Kenwood mobile. Cost almost $400. In 1988. Now I have a Yaesu FT2900 in my car, that cost less than $150. But it's too complicated for me. I had to buy a USB cord and the software to even set it up. That Kenwood was so simple. I wish they still made radios like that, just cheaper. A radio should be a radio, not a computer.

eBay is probably you best bet for that www.ebay.com

It highly depends on condition, serial number and installed options. A nice KWM380 in good cosmetic condition and no corrosion, but without any options and with serial number above 700 can be close to $3000. All options installed and good condition (like a HF-380 version) can go for more than $7000. A raggedy KWM380 with a serial number below 300 is probably more in the $1500 range. Hope this helps.