QUAD 303 NOISE

Hello All,

Having just completed a 303 revision I notice noise, At normal listening levels thnere is a hiss, white noise and a very low level hum. Increases with volume on both channels. Using a revised 33. When i substitute a 306 or 405-2 all is quiet. I have carried out only the dada revision. but all resistors meter ok. I have not touched any of the aging transistors . Can you point me where to look? I have installed multiturn trimmers and ril voltages are rock stadu 67/33.5 current is set at 10mV.

Hi EJP, 

The 33 has just had a full revision including all transistors changed to BC550. This noise doe not manifest itself when used with my 306 or 405-2. Could it be old 303 transistors on the way out? If so which ones should I replace first? Could it be resistors as all the 303 are old carbon types with the exception of the revision resistors. Regards Stewart