# Schottky diode as AM detector?

An old AM radio that passed down to me from my grandparents finally ceased to function after I accidentally dropped it and old parts inside got damaged. I ripped all damaged parts out and replaced them with modern equivalents. There is one thing I am having trouble replacing: the detector diode.

The original diode is 2AP9 (Chinese part, was THE detector diode in Chinese radio designs, similar to 1N34A,) a germanium detector diode that got shattered. I don't have any germanium parts any more (the germanium PNP transistors was replaced with silicon ones, but the amplifier is adjusted accordingly to make them work correctly after a few resistors get replaced)

However I do have a few Schottky rectifiers 1N5819. Are those good enough as detector diodes in AM radio? Do I need to adjust some caps and resistors to compensate the 110pF junction capacitance? (2AP9 have 1pF)

• I guess a BAT85 would be a better try. Maybe you have a G transistor left from which you could use the BE junction? – Wouter van Ooijen Jan 16 '15 at 16:42
• I dumped and replaced all old transistors actually. The 3AG1's have a planar BE junction and I am a bit worried about its junction capacitance. Those old parts didn't have such a specification! – Maxthon Chan Jan 16 '15 at 17:01
• @WoutervanOoijen That radio is older than me! I wouldn't trust anything in it at all (maybe except the PCB board itself) but I just didn't bother to replace all the caps and resistors. – Maxthon Chan Jan 16 '15 at 17:05
• Why not just try it? – Andy aka Jan 16 '15 at 17:27

• Those selling "1N34A" offers rebadged 1N4148 at inflated prices and the 0.7V drop will probably eat away the signal completely, since the receiver resonator is pretty weak. The board is probably 25-30 years old so it was all single sided THT. I will give 1N5711 a go. – Maxthon Chan Jan 17 '15 at 13:41