<<< Where are you obtaining the latest 0219 variable caps--from the manufacturer or from Mike's Electronics? This is certainly a very interesting finding.
73, Steve >>>
During the Pandemic I have been doing a lot of FSL experimentation, and have been buying these new "N50 384P" variable caps from Mike's Electronic Parts in batches of 7. Around March I first noticed that one of 3" Baby FSL's recently constructed was outperforming one constructed in 2018, even though all of the components were exactly the same. The only difference was that the variable caps used in 2018 had a "0217" series number, while the new ones received in 2020 had a "0219" series number. Both of those were received from Mike's Electronic Parts, with Oren Elliott as the OEM. Kind of curious about this, I substituted another "0219" variable cap for a "0217" variable cap in another 2018 FSL design, and immediately got the same noticeable performance boost (sharper tuning, and a greater sensitivity peak when zeroed in on the radio's frequency, which only happened when you tuned the FSL to exactly the right point). This "0219" variable cap performance boost was most noticeable on the extreme low band frequencies (such as 530, 531 and 540), although it was detectable all the way up to 1700 kHz. The effect was enough to motivate this fanatical tinker to replace all the FSL variable caps headed for the Rockwork Cliff this summer, ensuring that they all have new "0219" upgrades.
This is the first time that I'm sharing this discovery with anyone, Steve-- I had actually considered keeping it a secret :-)