The reason maybe, that yours was upgraded from a 38, and all that was done was important to sound improvement parts only, the circuit boards, to keep cost down.
If you read this from Stereophile, it says what the differences are, you should be able to see the differences if you study yours and compare, I had a very quick look and there’s not much I saw except for the board ID logo.
https://www.stereophile.com/solidpreamps/mark_levinson_no38s_preamplifier/index.html
This is the pic of a 38 (without transformer cover attached)
http://www.hifishock.org/galleries/electronics/mark-levinson/preamplifier/no-38-1b-mark-levinson.jpg
This is a pic of a 38S
http://www.hifishock.org/galleries/electronics/mark-levinson/preamplifier/no-38s-1-mark-levinson.jpg
Cheers George
If you read this from Stereophile, it says what the differences are, you should be able to see the differences if you study yours and compare, I had a very quick look and there’s not much I saw except for the board ID logo.
https://www.stereophile.com/solidpreamps/mark_levinson_no38s_preamplifier/index.html
This is the pic of a 38 (without transformer cover attached)
http://www.hifishock.org/galleries/electronics/mark-levinson/preamplifier/no-38-1b-mark-levinson.jpg
This is a pic of a 38S
http://www.hifishock.org/galleries/electronics/mark-levinson/preamplifier/no-38s-1-mark-levinson.jpg
Cheers George