Fuchs Amp Sizzles, Ground Noise

[guitarmv]

Yikes!

My Fuchs Frost 100 started making an ungodly ground noise two days ago, seemed to work fine yesterday, and now today not only is the ground noise back, it is also sizzling (only when taken out of Standby).

Bad tube? Worse?

[izzybell2810]

Yikes!

My Fuchs Frost 100 started making an ungodly ground noise two days ago, seemed to work fine yesterday, and now today not only is the ground noise back, it is also sizzling (only when taken out of Standby).

Bad tube? Worse?

When You say "ground noise" I take it you mean it's buzzing/Humming?

Sizzling? Is this out of the speaker or a noise inside the chassis? Could you be a bit more specific.

Dave.

[guitarmv]

Dave,

There is a hum, which gets much worse when I take my hand away from the amp (like the ByPass switch) or off the grounded part of a guitar.

The sizzle is pretty much that, an uneven sizzly static.

Two days ago it was making the ground-related noise, yesterday it was fine, and today there is the ground noise and the sizzle.

Thanks!

[guitarmv]

Also, what I am calling ground noise is quite loud. At first I thought is was bad wiring in my guitar, but it did it with another. This time I noticed it without any guitar or cable plugged in.

[bnwitt]

Have you tried replacing your vacuum tubes with known good tubes? That amp is a little young to have other problems and If I know Andy it's built well.

[Enzo]

It won;t be the tubes, they wouldn;t know if he was touching the guitar or chassis.

Does the amp do this at other l;ocations? Are you plugged into an outlet strip? Are you SURE the outlet is properly grounded? Does the power cord third prong have electrical integrity back to the chassis?

[izzybell2810]

Also, what I am calling ground noise is quite loud. At first I thought is was bad wiring in my guitar, but it did it with another. This time I noticed it without any guitar or cable plugged in.

Is the Amp grounded properly? Check the ground wire is sound!

Dave.

[bnwitt]

It won;t be the tubes, they wouldn;t know if he was touching the guitar or chassis.

I was speaking more to the sizzle symptom than the hum.

[guitarmv]

It occurs to me that I did not check the clean channel, so I can hunt down where the problem is, as in tubes or otherwise.

BTW, regarding opening amps and the danger therein, I found an article describing a capacitor discharger using a 10W 5% High Ohm Cement Power Resistor 25Kohms 5%, but have not been able to find it again. I have some 10% 5w 250 cement resistor, can this, or a range of resistors, be used to make this discharger?

[guitarmv]

Yeah, it is making me wonder if the house itself is having a grounding issue. Nothing has changed here, all my power strips, etc, haven't changed

[guitarmv]

"Ground OK" on one of my power strips

[bnwitt]

If you leave your amp on (power switch and standby switch) with volumes up and unplug it from the wall while strumming on your guitar for 20 seconds as the sound drops off you will get the internal voltages down to around 20 volts. You can also ground pin 1 or 6 of V1 to the chassis with a jumper wire for 20 seconds (with power and standby switches on and the amp unplugged ) using the plate resistor as the current limiting device for the discharge. I would not use that 250 ohm resistor as the limiter as the value is too low. When you are done with either one of these procedures use you meter on voltage DC to check voltage at the DC output of the rectifier to make sure it is not still high.

[guitarmv]

If you leave your amp on (power switch and standby switch) with volumes up and unplug it from the wall while strumming on your guitar for 20 seconds as the sound drops off you will get the internal voltages down to around 20 volts. You can also ground pin 1 or 6 of V1 to the chassis with a jumper wire for 20 seconds (with power and standby switches on and the amp unplugged ) using the plate resistor as the current limiting device for the discharge. I would not use that 250 ohm resistor as the limiter as the value is too low. When you are done with either one of these procedures use you meter on voltage DC to check voltage at the DC output of the rectifier to make sure it is not still high.

Great info! Thanks

[loudthud]

Does the amp have a detachable IEC power cord? I've seen brand new cords that didn't make the ground connection. Try a different cord.

[guitarmv]

Alright, so I had taken the head out of the cabinet to have access to the tubes (freaking beautiful inside there) and then put it together, tried a different chord, and the problem isn't there.

I am going to wait until tomorrow before I let the tension out of my shoulders (over the possibility of having to ship this thing off-island). I will post if the problem persists.

Thanks for all the great help!!