Diode identification

[Peter Blackett]

Hi,
just wondered if any of you know an equivalent to the diode type 
1S1555   ?
seems to be a Japanese part [ used in a Yamaha keyboard ] .
after doing a web search I'm told it might be equivalent to a NTe 506 
[ I think this is a Usa based company that does equivalent parts ].
anyone got any suggestions .
the diode is used in a switching circuit with about 30 v dc on it .
Is there a book similar to the Towers tansistor guide but for diodes ?
regards Peter