I wonder if anyone had any sources and books, preferably in English, regarding the short-lived Gemeiner Pfennig tax in the Holy Roman Empire. If anyone had any idea how it functioned, that would help as well. I'm also seeking information regarding the Reichstürkenhilfe, which as I understand was a tax levied during wars with the Ottomans, to pay for the cost of the Imperial Armies. I'm trying to do some work on my PoP timeline and a Pfennig tax plays a major role, so I believe I need to try and understand it a bit more.
Any other information regarding other special taxes that might be levied by the Emperor would be of use as well. I am pretty sure the Reichstürkenhilfe is the only one, but there may be others.