From Skipp: Here is the information on both the old and new versions.

The FL-6 follows a fairly common theme with VHF and UHF pre-amplifiers of 
that generation, including GLB and other brands.

The first version FL-6 active device is/was a 3N201 FET. While it might be 
a noisy device compared to a newer generation product, it is and was the 
technology of the time, being three or more decades past. My how time flies.

The second generation FL-6 looks like it moved over to using a bipolar
device, the "6033" diagram provided part number doesn't look like anything 
special I can recall from a normal mental fog. Maybe someone can do a quick 
ID if they're familiar with the circuit or device.

More recent brands and popular "home-brew" VHF pre-amplifiers have been 
based around the BF981 dual-gate MOSFET. Noise-figure-wise the BF981 
appears to be better than the older 3N201 and still fairly easy to obtain.

The newer package style SOT-103 is an improvement over the older 3N201
having a TO-72 (metal case) package. In a casual VHF preamp experimenter
situation, I still wouldn't have a problem playing with a 3N201 device. 
You just need to be mindful of the package device leads and all that's 
involved with them being "so long".

If you could deal with modifying the active device mounting and connections,
a bit of FL-6 improved performance could be realized by "working in" the
newer BF981. There might be relatively modest differences in the optimal
gate bias values, but there's plenty of decent working pre-amplifier 
examples found on the web. That is if your current active device doesn't 
appear to be working and you want to replace it (with something that does 
work).

In older times, using the FET could mean less noise, but also notably less 
gain compared to a Bipolar transistor. In fact, some older VHF pre-amplifiers 
by device used and applied circuit, could appear to be kind of numb or even 
not working well when given an initial glance/test.

Still in older times, a bipolar device (transistor) was generically assumed
by the rules of the era to have more gain (versus a FET) and possibly less
noise (depends on the specific device and generation). So the FL-6 switching
from an older Dual Gate FET to a bipolar transistor might have been made for 
the just described story.

See which one you have; don't be fooled by what you might think is measured
low performance being a bad device, but also understand you can fairly easily
improve both the original DG-FET or the later bipolar if you wanted to try 
your hand at a bit of home-brew upgrading.