Counterpoint SA-5000 P.S.U part identification needed

[Tubologic]

Hello,
I'm reparing the H.V regulator section of a Counterpoint SA-5000 preamp. Most semiconductors (all transistors and many diodes) were found dead. (shorted or open). Still I have a problem identifying D503, a strange device looking like a transistor in a TO-39 package with a cut lead. It is marked C.I.L 500/150 and this reference cannot be found in any know Semiconductors Databases. Very likely a diode or a selected zener ? This part is dead,measuring about 800 ohms both ways. So,here I'm stuck...
As I don't have the SA-5000 schematic (Impossible to find on the web and I'm not ready to pay $ 100.00 to Mike to get a copy) I don't know the exact function of this diode in the circuit ,nor can I devise a possible substitution. I would greatly appreciate If anybody here with some experience (or schematic) could help me to identify this part (D503) or advise a sub. The HV power supply in the SA-5000 looks quite complex (Tube rectification followed by a S.S pre-regulator and then tube regulation !) and know to be failure-prone. I figured out the sequence of (catastrophic) events who finally leaded to the complete destruction of the power supply (including the power transformer!) All started with an open (underrated) 470K bleeder resistor... but this is another (long) story. Looks like a over-complicated and poorly designed circuit to me. Thanks to all for your help and advices...

[ferrstein]

I have a parts list, I'll look it up this evening.

Or drop me a line. I'm new here so I can't email right away.

Great site, I hope to learn a lot here!