When you place だけど in front of a verb, you must omit the declarative だ. You can not place だ between a verb and けど. だ (in this context) is only used with な ajectives and nouns.
For example:
土曜日だけど、仕事です。It is Saturday, but I have work.

静かだけど、ねられない。It is quiet, but I can not sleep.

行くけど、泳げないんです。I will go, but I can not swim.

As you can see だ is omitted in the third sentence.
Also, for な adjectives the な is not used, since we are not modifying a noun.

P.S. (these same principles apply to から, in the context of because or since.)

Hope this helps