so ive been sitting on doing the mars/cap mod on my FT-857D for probably two years now and finally just did it last weekend. pretty straightforward honestly, just that one diode to remove and it opens up the tx range. wasnt planning on transmitting outside the ham bands obviously but i wanted it for some EMCOMM stuff we do locally where we sometimes need to hit MURS or FRS adjacent freqs depending on the situation.

while i had the lid off i also swapped out the stock electrolytic caps near the PA section because a couple of them were showing some slight bulge on the tops. not bad yet but you know how it goes with gear thats been running hot for years. grabbed a matched set from mouser, same ratings but slightly higher voltage tolerance. no idea if it actually changed anything measurable but peace of mind i guess.

the bigger thing i did was add a cheap little muffin fan underneath the rig on a temp-switched circuit. the 857 runs warm anyway and i was always nervous about it during long digital sessions. used a LM35 sensor zip tied to the heatsink and a simple comparator circuit to kick the fan on around 45C. its kinda ugly but it works and the rig stays noticeably cooler now on PSK31 and JS8 stuff.

anyone else done anything interesting to their 857 or similar rigs? curious if the noise floor on mine is just what it is or if theres something worth doing on the frontend

the fan mod is smart, ive seen a few 857s with cooked finals and almost every one of them was used heavily on digital modes without any extra cooling. the stock thermal design was probably fine when the rig came out and people were mostly using it for SSB portable ops but running WSPR or JS8 for hours is a completely different thermal load.

on the noise floor question -- theres a front end filter mod floating around that supposedly helps with IMD in dense RF environments, involves adding a couple of toroids and swapping the input filter topology slightly. i never did it myself but a guy in my club who lives near a AM broadcast tower said it made a noticeable difference for him on 40m. might be worth searching the reflector archives, i think it was originally documented by someone in Europe. the 857 frontend is decent but not amazing and if youre in any kind of urban environment it can get a little overwhelmed.

also curious what caps you used on the PA section, i have an 857 thats about the same age and havent looked inside in a while

yeah the mars mod on those is easy, did mine years ago. just dont forget to do the alignment check after because occasionally the tx power calibration gets a little weird on the edges of the expanded range, nothing major but worth a quick check with a dummy load and wattmeter.

one thing i added to mine was a better cooling solution on a slightly different approach -- i just drilled a few extra ventilation holes in the bottom panel in a pattern that doesnt compromise the chassis rigidity and lined them with fine mesh to keep debris out. not as active as your fan circuit but the convection airflow improvement was actually measurable with a cheap IR thermometer. dropped idle temps like 8 degrees or so.