[hoyquest]

Have anyone used National PE-247S on K20D? It is old flash used for flim SLR. No sure it is fine to use it on K20D.

[goldenzebra]

You should check the flash trigger voltage.
I'm not sure (and don't know) what is the maximum value for the K20D (you should ask PENATX service to have a qualified answer).

I read in one of the threads - Which trigger voltage have you verified to work? here (by Class A member) the following:
According to this thread (sorry, in German) "Wieviel Spannung verträgt die K10D?" Pentax confirmed multiple times a maximum flash trigger voltage of 30V for Pentax DSLRs.

To be at the safe side - 6v (and less) considered safe.
Yaniv