It's really fascinating... I bet you could see my eyes shining as I was walking through. We were guided by a very nice gentleman who still had memories of the Austro-hungarian empire and spoke very fluent German. He even did a bilingual German-English tour as there was a couple from Belgium.
The address is
Magyar Elektrotechnikai Múzeum
Kazinczy u. 21
H - 1075 Budapest
If I remember correctly that's close to the Opera M1 stop.
Their website
http://www.emuzeum.hu used to be Hungarian/German/English but I can't find anything but the Hungarian version now.
This museum was one of the two "triggers" for my very first tour to Budapest last summer. The second was the news of the UV streetcars going out of service with the closure of the Freedom bridge.
