Strange Brew

[USAPatriot]

...look what's inside of you.

Here's an oddity and even I can't explain it. Last week one of my preamp tubes in my JCA22H popped it's cork from some transient...I heard the pop inside the amp...and then all of a sudden I'm getting FM music through my cabs. Again. Dammit. So I found the offender in V3 and replaced it with one of the original China tubes for the moment and that cleared things up. While I was there I put in new power tubes, a set of electro-H's EL-84's, All is well and everything back to normal.

Almost. The strangest thing popped up and you'd never think to look for a problem here, but when I turn the crunch channel volume down...as in OFF...the music comes back, big time. It's not in the OD channel, it doesn't matter what the master volume is set at. But turn the crunch knob all the way left, and I hear rock n roll. Oddly, the JCA only picks up my favorite radio station in the area. None others. And if I nudge the crunch up away from zero by the slightest amount, the radio's gone.

What in the world? :scratchch

I don't actually care since who runs their crunch at 0 (?), but it's an interesting thing, nonetheless. -Rod-

 

[glassman]

Re: Strange Brew

That's odd.

AM radio reception in a guitar amp isn't that uncommon but FM reception requires a number of things to come together for it to happen. To demodulate FM in a guitar amp, you almost have to have some sort of parasitic oscillation in the MHz range to be able to access the carrier frequency. Then you'd have to have somewhat substandard grounding to be able to amplify it.

Weird.

 

[USAPatriot]

Re: Strange Brew

It IS wierd, Glassman, and yeah, I knew that. FM isn't as easily propagated as AM is. AM skips, isn't line of sight, is propagated and received in a totally different way than FM is...which makes me wonder about something else not mentioned. I have a few feet of steel wire that I have hooked to my GT-10 as a ground. If my amp gets too hissy due to dry air or whatever I just take my sock off and put my foot on the wire. Silence. I wonder if the wire is acting as part of an antenna circuit through the GT-10 and all the cables? Maybe turning the crunch knob all the way left puts the amp into standby mode and lets all the pieces work? I just have to nudge that dial for the music to go away, so it seems a reasonable explanation as unreasonable as the whole thing seems. I had FM radio come through my el-cheapo rolled steel curtain rods back in Colorado Springs sporadically for a number of years. Some things just don't have an easy explanation even when it's right there in front of me. -Rod-

 

[Toe-Knee]

Re: Strange Brew

It sounds like the pot isnt closing entirely and the grounding for the pot itself isnt 100%.

You can easily stop rf pickup in guitar amps by installing a 0.1ufcap from the sleeve of the input jack to ground this stops anything that is picked up between the guitar and the amp being amplified.

I had a similar issue to yours in my very first amp build and i just made sure the ground connection was solid and it was gone afterwards

 

[USAPatriot]

Re: Strange Brew

It sounds like the pot isnt closing entirely and the grounding for the pot itself isnt 100%.

You can easily stop rf pickup in guitar amps by installing a 0.1ufcap from the sleeve of the input jack to ground this stops anything that is picked up between the guitar and the amp being amplified.

I had a similar issue to yours in my very first amp build and i just made sure the ground connection was solid and it was gone afterwards

I'll have to check that out, thanks. It shouldn't even be happening, really. -Rod-

 

[Gearjoneser]

Re: Strange Brew

I have a few feet of steel wire that I have hooked to my GT-10 as a ground. If my amp gets too hissy due to dry air or whatever I just take my sock off and put my foot on the wire. Silence. I wonder if the wire is acting as part of an antenna circuit through the GT-10 and all the cables? Maybe turning the crunch knob all the way left puts the amp into standby mode and lets all the pieces work?

:scratchch

 

[USAPatriot]

Re: Strange Brew

:scratchch

It makes sense.

Do people still throw rocks at the trains running through Chatsworth Park? I seem to recall that car carriers were favorite targets of some of the local thugs there. I was raised in Woodland Hills in the 70's -Rod-

 

[Gearjoneser]

Re: Strange Brew

Do people still throw rocks at the trains running through Chatsworth Park? I seem to recall that car carriers were favorite targets of some of the local thugs there. I was raised in Woodland Hills in the 70's -Rod-

A few years ago, Chatsworth Park was closed with a big fence around it.
It's because they found high levels of lead in an area that's for picnics. Back in your days here and before, when they used to film westerns there, the amount of shotgunning created a lead problem in the soil. I wonder if it'll ever reopen. I like that park, and have even done band pics at that train tunnel that's famous in movies.

Also, the tunnel near Rocky Peak is where the worst train wreck in US history occurred. I was one of the only mountain biking witnesses of it, and had a camera. That was a few years ago. Maybe I'll PM you some pics of it when I get around to it.

 

[USAPatriot]

Re: Strange Brew

Yeah pics would be great! I remember the westerns but the lead levels? Solid lead doesn't leech into the soil that way. Yeah the pellets would be a hazard to anyone eating them, but that's not advised for pellets or anything else you find in the ground. Lead salts would be another matter. Too bad they closed the park. It's maybe the largest piece of open land in LA. Santa Monica State Park is larger but if you go to the "trailhead" up on old Mulholland, you can see what a joke that is. They designated it a park to keep developers out but didn't do any improvements to make it useful, sans a small portion accessible from Topanga Canyon, just a few acres. What a waste. -Rod-