I am currently restoring a HeathKit SB-303. The receiver is missing Diode D513, G.E. STB-620 or IG1270, on the IF/Audio PCB. This is part of the S-Meter amp circuit. This diode is Stabistor. If you have the spces for this diode or have a source for it. Please advise. Also will consider purchasing the entiere IF/Audio PCB if necessary.