Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Crate G40C noise on power up.
Not more than 2 seconds of hum then amp works fine. 
Replaced caps  and diodes in power supply,  blown chip and JFET in chorus section. That works fine now as well.
Any ideas?

Did this 2sec hum happen *Before* you replaced parts?
If so the amp may be acting normal.
Phil.

Try disconnecting the speaker and measure the DC voltage reading on the speaker connections. Look to confirm a small 500mv to 1v on the output while metering it on power up. This will tell us if the noise is a DC offset on the output making noise. Sure this can be the amp working normally and as the pro's put it "The amp just wakes up stupidly".

So for that second or two the amps voltages are settling in and it is not perfect so it can make noises. I recently had a Fender amp that put out 750mv to 1v on power up which will then drop to 5mv after 2-3 seconds and it was not normal. However, tracking down the cause of the problem led to a tiny bit of shotgun part replacement, which we don't recommend. In my case I had suspicions that certain transistors were stressed in a failure of other transistors that I had already replaced. I WARN YOU THOUGH... that these types of symptoms will drive even the greatest techs crazy trying to trouble shoot the cause. In the end it may not be a repairable issue and the amp is actually functioning fine. I guess confirming Phatt's question is the best place to start.