RHF wrote:

FO&A,
.
Per DXing.Com = http://www.dxing.com/rx/sw8.htm
.
* Units produced after 03/31/95 (S/N = 5C) feature
a preamp circuit for the telescopic whip antenna.

Drake didn't add a preamp. They improved the impedance matching to the
whip antenna for better signal transfer (sensitivity).