I've got a Russian Red Bear MK60 head, and when I select the "high-gain" input with the overdrive, there's a constant rhythmic "tweet tweet" sound in the background.
When playing in a band situation, the noise is drowned out by the music, of course, but I wonder a) if it's a Bad Thing, and b) how to cure it?
Bob-I wrote:Perfectly normal. Everything I own does that, SS and tubes.
A million years ago that was caused by over the horizon radar stations prevalent along our coasts. We used to trap it out using a little notch filter in the line supply. I haven't heard it in years.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Bob-I wrote:Perfectly normal. Everything I own does that, SS and tubes.
Thanks for the reassurance, Bob
Skyboltone: so it's caused by radar??
tweet tweet
Well, in BobI's case it may be the darn Unicorns again...... but in yours it could be. Where do you live? Near the final approach corridor or departure path of an airport? Does it occur other than in your guitar amps? Tracking it down may take some creativity. Get some ferrite dounuts from http://www.amidoncorp.com/ and try running your transformer leads through them. Keep the 120AC leads as short as possible in the chassis. It's almost certainly RF induced.
I've heard funny artifacts from those touch on touch off table lamps too.
Good Luck
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Very interesting stuff. Is this RFI related to the use of a pair of small caps from the line and neutral to ground ahead of the PT primary, presumably to ground it out before it gets into the amp? I imagine the cap value must be small and calculated very carefully, no? What is the formula?
David Root wrote:Very interesting stuff. Is this RFI related to the use of a pair of small caps from the line and neutral to ground ahead of the PT primary, presumably to ground it out before it gets into the amp? I imagine the cap value must be small and calculated very carefully, no? What is the formula?
David, I don't have any of my old Ham references here with me. I don't recall how we used to trap out the over the horizon stuff years ago. Really, like maybe 30 years ago. It took a small choke and cap, in parallel, tied from either side of line to ground. A tank circuit tuned to an odd harmonic of the radar frequency. I think. The ferrite beads from Amidon are way easier. They are used in all kinds of electronic equipment, especially medical stuff, and don't interfere with the circuit.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
It's a weird one, for sure. And there was me thinking it was some kind of internal oscillation thing...
I live about 7-8 miles from a (provincial French) airport. We're playing out of town later this week - I'll turn everything up and see if it still tweets when we're 40 miles away...
I've had the same issue in a few of my amps, back where I used to live. It was in close proximity to the airport's Non-Directional Beacon, or NDB. The signal was a periodic morse code identifier. If you do live close to an airport or on the final approach or departure routes, that could be the problem. Try this link to locate airport navaid locations and frequencies in your area: http://www.airnav.com/ hth
choose your airport here and you will see the VAC (visual approach cart?)
radio beacons are named with 2 or 3 letters and the frequencie (FA375 for ex. and the morse code is FA)
they even got an English version on the home page
search in AIP then VAC or IAC for larger (instrumental approach) view.
your amp may have them...but input grid resistor makes a big change for RFI.
Two years ago my "new" 18w was iddling quietly in the tower control were i work(wonderfull place for radio pollution problems), and suddenly a pilot was speaking(shouting) through it
I put 47ks' on the V1 socket grid pins and now i could play guitar without being disturbed by the pilots
choose your airport here and you will see the VAC (visual approach cart?)
radio beacons are named with 2 or 3 letters and the frequencie (FA375 for ex. and the morse code is FA)
they even got an English version on the home page
search in AIP then VAC or IAC for larger (instrumental approach) view.
your amp may have them...but input grid resistor makes a big change for RFI.
Two years ago my "new" 18w was iddling quietly in the tower control were i work(wonderfull place for radio pollution problems), and suddenly a pilot was speaking(shouting) through it
I put 47ks' on the V1 socket grid pins and now i could play guitar without being disturbed by the pilots
cheers
Excellent! Who wants to be disturbed by pilots, after all?
choose your airport here and you will see the VAC (visual approach cart?)
radio beacons are named with 2 or 3 letters and the frequencie (FA375 for ex. and the morse code is FA)
they even got an English version on the home page
search in AIP then VAC or IAC for larger (instrumental approach) view.
your amp may have them...but input grid resistor makes a big change for RFI.
Two years ago my "new" 18w was iddling quietly in the tower control were i work(wonderfull place for radio pollution problems), and suddenly a pilot was speaking(shouting) through it
I put 47ks' on the V1 socket grid pins and now i could play guitar without being disturbed by the pilots cheers
Hi Klingo:
Do you guys use numeric radar transponders over there? When ATC radar sweeps an airplane in the US, there is a little light on the transponder that blinks twice. It's called interrogation. This occurs about every 15 to 20 seconds. That's what put me in mind of the old defence radar stations in the old days. As those monster antennas swept the horizon, they induced the primary frequency into every overhead power and communication wire for a 100 miles around. As this UHF signal traveled down the power lines and into electronic equipment, the power supply diodes would "detect" it and produce a product that was further amplified by the device. The sound was not so much a tweet tweet as a very regular buzz buzz. Anyway, marker beacons and ILS approach beacons are pretty tightly focused low power beams right down the runway center line and tilted up as in ILS and straight up as in Marker beacons. I think the Cap's problem is radar.
If the grid resistor business doesn't pan out, try ferrite beads.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Wow I never gave it any thought as to how many air ports I have around me + living 5 miles from the one at fort knox Ky. There is 3 things that will help this 1. aluminium 2 brass screen and ferrite dounuts. You can buy cheep aluminium roof flashing and put it inside the cab or use brass screen inside the amp cab or like skyboltone said you can Get some ferrite dounuts. Hope this helps some and Im sure to try one of them. I have 5 airports within 40 miles of me.
That little teety sound has drove me nuts and until now I didnt know what it was
Hope this helps out
Darrell
