GK 250ML Blowing Fuse

[sweatyk]

That has pretty stable timing. I'd say it's either related to the chorus, or some kind of outside electronic noise getting picked up.

I had everything turned off in the room and still got the noise. Could something be coming from the chorus circuit even when it is not engaged?

[sweatyk]

Also to note..... when I first power it on it's not there. But it faintly starts after about 5 to 10 seconds and gets progressively louder to what you hear in the video.

[The Dude]

I agree- probably chorus related. That said, it could be a chorus circuit problem, or the chorus could be reacting to an existing noise in another circuit. Is the noise there with the chorus off?

[sweatyk]

I agree- probably chorus related. That said, it could be a chorus circuit problem, or the chorus could be reacting to an existing noise in another circuit. Is the noise there with the chorus off?

Yes it is there with switches off or on

[Enzo]

Put your cell phone in the other room.

[sweatyk]

Put your cell phone in the other room.

I have.....and it still does it. Now would be a good time to own an oscilloscope

[sweatyk]

I would like to also note that once the shorted parts were replaced I had my guitar plugged into the amp when I powered it up. I felt like I had resolved the issues that were causing the fuse to blow. As a last action I decided to replace C51 & C52 due to their age. My thought on this was fresh caps will give a longer life span. A novice move on my part but thought it would make a difference. Once installed I powered the amp up with no input source so the caps could get some juice through them. That's when I noticed the latest cycle of chirping sound. So it could have been doing this prior to the 2 cap changes. I've been tempted to put the originals back in to see if anything changes. Thoughts or recommendations being I do not possess an oscilloscope?

[g1]

Listen for the speed of the chorus when on. Does it sound like the same repetition rate as the 'chirp' ? Or some multiple of it?
I doubt new filter caps could have caused this issue. Maybe something related to the work, but not the components themselves. So putting the old back in would be a waste of time I think.
Is it noticeable at normal playing volumes, or is it something you have to crank everything up to hear?

[sweatyk]

Listen for the speed of the chorus when on. Does it sound like the same repetition rate as the 'chirp' ? Or some multiple of it?
I doubt new filter caps could have caused this issue. Maybe something related to the work, but not the components themselves. So putting the old back in would be a waste of time I think.
Is it noticeable at normal playing volumes, or is it something you have to crank everything up to hear?

The volume has no effect on it. Always the same level. I guess if you play loud enough you won't hear it

[Helmholtz]

I would be more annoyed with the hum than with the faint "birds".

As a test you might wire the old caps in parallel with the new ones.

[52 Bill]

I would suggest checking or replacing the small filter caps for the power supplies that feed the chorus section. There are a few small radial caps that will fail and cause all sorts of odd problems and hums.

[sweatyk]

I would suggest checking or replacing the small filter caps for the power supplies that feed the chorus section. There are a few small radial caps that will fail and cause all sorts of odd problems and hums.

Thanks for the suggestion. I'll pull them and check their value and replace them

[sweatyk]

I can muddle my way through schematics but still have issues identifying signal paths. If I'm looking at the chorus circuit correctly C97 is one of the electrolytic caps.? The service manual list it as a 3.3 if @ 50V.......the one in the amp is 25V. I have a small surplus of 3.3 if @ 35V mini caps laying around. I'm sure they would be ok to use. What others in that circuit should I be looking at?

[52 Bill]

The chorus and echo stages are on page 10 of the schematic book. The filter caps that I was suggesting that you check and replace are C98 and C99. They filter the power supply voltage going to the clock circuit. It looks like they are 220uF caps.

[sweatyk]

The chorus and echo stages are on page 10 of the schematic book. The filter caps that I was suggesting that you check and replace are C98 and C99. They filter the power supply voltage going to the clock circuit. It looks like they are 220uF caps.

Well C98 and C99 were not this issue. Any guidance on where to start? Is something that would require an oscilloscope to further troubleshoot?