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Dirty-South Blues Harp forum: wail on! >
So I am playing through my VHT Special 6...
So I am playing through my VHT Special 6...
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ReedSqueal
224 posts
Dec 19, 2011
7:36 PM
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Playing through my new-to-me VHT Special 6. All set at my usual settings. Turn down my mic volume to take a breather; then I hear Country music playing out of the amp speaker. WTF?
Very faint but 100% unmistakable and discernible, a local FM radio station.
I've played though amps in years past with a guitar and never have heard FM through an amp.
Any explanations?
Edit: I just assumed it was FM, maybe it's AM?
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Go ahead and play the blues if it'll make you happy.
-Dan Castellaneta
Last Edited by on Dec 19, 2011 8:18 PM
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FMWoodeye
148 posts
Dec 19, 2011
8:56 PM
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Sounds like something to do with electricity and radio waves.
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MJ
339 posts
Dec 19, 2011
9:24 PM
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"here ya go, something from Aiken Amps:
Q: My amplifier is picking up radio stations - what causes this, and how can I fix it?
A: RFI (radio frequency interference) is usually caused by bad cables, bad solder joints, long unshielded wires from the input jack to the first tube and/or bad ground, no "grid stopper" resistor on the grid of the first preamp tube, or no tube shields on the tubes. In some cases, RFI can get in on the AC mains. Possible fixes:
First, unplug the cable to see if the RFI goes away. If so, it is likely the cable or the guitar picking it up, or lack of grid stopper resistor on the first tube.
Try pulling out the preamp tubes and putting them back in a few times - they can have corrosion that is causing rectification of RF, and the wiping action of removing/replacing the tubes can help clean them in a pinch.
If it has isolated input jacks, put a 0.01uF cap from the *ground* side of the jack directly to the chassis at the closest point, such as on a ring terminal mounted behind a switch, or a on a pot or something. This will kill RFI deader'n hell in most cases. Ceramic disks from Radio Shack will work fine, or any kind of film capacitor. Sometimes you can test this to see if it is the cause by sticking a wire or paper clip on the metal body of the guitar cable where it plug into the amp and touch it to the front panel on a bare metal spot.
If it has no grid stoppers, put a 10K-68K resistor on the grid pin of the first tube, right at the socket.
Resolder the joints on the sockets, jacks, and components in the input stage.
If it has no tube shields, add them.
Install an internal AC power filter, such as those made by Corcom (available from Digi-key). You must use a filter appropriately sized for the mains voltage and current draw of the amplifier.
Install a clamp-on ferrite core on the AC cord right at the point where it is plugged into the amp.
All manufacturers should use one or more of these to insure they don't run into the same problem you've experienced. If the amp in question had isolated input jacks, the 0.01uF cap to ground right at the jack is usually the best solution. A "quick and dirty" test is to take a paperclip and touch it from the body of the cable where it plugs into the amp and short it over to the metal front panel. If this kills the radio station, the 0.01uF cap is the way to go. Of course, this won't work with a plexi front panel.
Randall Aiken"
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