Hi and thanks for reading this post.

Not sure why but my quad 405-3 is making weird noises.

When switched on it works ok for the first five minutes then it makes a loud crackling noise for a second, a minute later it crackles again and this is loud, i had the volume low but it nearly blew my tweeters then it started to hum as well.

Not sure where these noises are coming from but I just had the amp boards serviced by the manufacturer so theoretically these should be okay, also i fitted a new 35 amp 200 volt Vishay bridge rectifier replacing the stock rectifier bridge, a 7amp PM7A2Q, and installed new smoothing capacitors, the stock ones were 10k uf each, due to tolerances the new ones measure in at 9k uf, the only component left untouched is the transformer.

Does the noise i am experiencing indicate a transformer problem, Is there any way you can advise.

By the way, i am measuring infinite resistance between the primary and secondary and 0.5 ohms across the secondary.

The secondary is actually two secondaries parallel connected and should be approximately 35 volts each with my voltmeter i am reading a fluctuating voltage which varies between 72 and 76 volts.

Many thanks in advance. John.