Something that affects my BRG performance, at least slightly, is whether the unit is really grounded or not. My function generator and power supply use earth grounds.
Many electrical outlets are poorly wired and are not really grounded. It is mostly a safety issue and appliances, lamps, radios, etc, will all work fine plugged into an outlet that is not earth-grounded, even three-pronged devices.
I noticed that there is now available at Home Depot a $3 (!) outlet circuit checker, made by Sperry Instruments. It is a little yellow box that plugs into standard 3-prong AC outlets in the home and has three lights, combinations of which indicate problems with the circuit (hot-neutral reversed, neutral open, ground open, ground-neutral reversed, etc).
I have one that is decades-old (which cost a chunk at the time,) but have misplaced it, so had not checked the outlets on which I was running the BRG. Turns out that most of the time in my home, I have been using a non grounded outlet.
This probably explains the difference I see in the beam at certain frequencies between running at home and running at my parent's. I would get a few pearls in the 500-700 range at home until I started using a grounded outlet. The beam also looks better - stays pure mauve over a wider frequency range (at less efficient freqs, will typically get a white/blue corona).
I recommend getting one of these devices and checking your outlets.
Just a reminder of something about which I have posted in the past. It may be important to ensure that the BRG be plugged into a grounded outlet.
One of my BRGs appears to function well when it is powered through an outlet which has no ground. It is a three prong outlet but the ground is not connected as evidenced by testing with a Siemans outlet checker, available at Home Depot for about $3. It runs at 100-110W with SWRs 1.2 - 1.3. It produces effects and can occasionally be felt. The beam looks fine and the audio tones can be heard starting about 1500Hz up.
When it is plugged into a grounded outlet it runs at less power (around 100W) and much worse SWR of 1.5-1.7. The beam looks the same or better as in the non grounded outlet. But, the audio tone is much louder and can be heard as low as 440Hz. The effect seems stronger and I can often feel it as opposed to when plugged into the non grounded outlet where I can only rarely feel it. Another BRG I built in the past appears to work equally well whether the outlet is grouded or not, the tones being strong either way down to 300Hz or so.
It is worth the $3 to get the checker to determine if outlets are properly wired. It also determines other wiring problems (swapped hot and neutral, e.g.).