I live in a condo unit; permanent ham antennas prohibited by the HOA's rules. All of my HF antennas (and I have many) are hidden or temporary. That's what I've done so far:

• build a magnetic loop;
• use push up pole with either vertical or horizontal dipoles mounted on top,
• erect temporary verticals with some kind of ground system,
• the attic I have access to is house to quite a few antennas, including 2-element wire beam.
• strung a wire doublet under the eves of the roof.

It is well established opinion that improving antenna system is the easiest way to improve signal in far field, but after half a year of hammimg I'm about to exhaust the antenna route. So, I decided to try an amplifier. I decided that the legal limit amp is too much for the dense residential I live in, and narrowed the search to 500W Elecraft KPA500 solid state amp. I ordered it in the kit form and easily assembled it during the last week, to test it over the weekend.

The kit is high quality, very easy to assemble and the instruction manual is well written with attention to details. I had no problems during assembly. I recommend the kit version (they also sell the amp assembled) not because it is cheaper (it is, a bit), but because it is fun project to do and it will not be a scary black box to you should you open it in the future for maintenance or cleaning.

I used the amp with several antennas, driving it with 30W from Icom IC-7300 radio; I used Palstar AT-AUTO tuner to match to my multiband doublets; it all went well. I was able to have a long chat in Russian on 40m with distant station in Bulgaria (LZ3TV), something I did not dream doing before. The antenna was a multiband doublet under the eves of the roof at 20 ft / 6m high. Of course, the other side had beam antenna and legal limit amp, but I feel that before, without the amp, this wasn't a possibility.

I made many contacts, state-side and DX, on Hy-Gain AV-12AVQ antenna up 25ft / 7.6m on fiberglass pole in vertical dipole configuration. This antenna wasn't that good for long haul DX before (see this post), without the KPA500 help. Here is the map of this weekend's contacts, all made using KPA500's 500W little push:

The amp is very easy to use; I connected it between the radio and the tuner (i.e. antenna output of the icom connected to the amp's input and amp's output is connected to palstar's input). The only other connection is the "send" line from Icom to KPA. The amp is sensing and switching to the right band when the tuner is used (I use tuner when the amp is in standby, it does the switch nevertheless). It is small, silent, well made piece of radio gear. Future will tell, but for now I am very happy with this addition to my shack.