Fender Deville has a static, radio signal like sound

[carl1987]

I had two shows in the past week, and i had to stop the set because my amp all of a sudden gets this terrible static sound that almost sounds like it is picking up radio signals. The volume of the guitar gets cut as well. I am able to turn the amp off then back on an the problem goes away. But a minute into playing it returns to the static/buzzing. It is not from any of my pedals because i have now tried the amp going directly in with just a shielded quarter inch cable. My output tubes are only 6 months old but my preamp tubes are pretty dated, can this be the problem?

[Ronsonic]

There are so many previous threads with detailed discussion of the rotten solder joints throughout the preamp section of those amps. It needs FX loop jacks cleaned and or resoldered and needs resoldering across the control panel.

The older ones have input jacks that tend to fall apart. THey are the ones that look like the FX loop jacks. Both type usually need more solder.

[km6xz]

The radio like signals, with reduction in desired signal level sure sounds like it IS radio. A strong RF field created by a transmitter will cause just those symptoms. There are several ways RF energy can get into the aamp; Input differential mode, common mode, ac mains coupling, speaker lead pickup etc.
The problem might only be your proximity to the RF source or it can be a combination of poor grounding, a nearby RF source and lack of high frequency bypassing in the input circuit of your amp. I would wager that it goes away when you move your amp to a different venue.
Does the gain control of the amp change the volume of the noise? Doe the ratio of desired signal to noise/RF signal change when adjusting the gain/volume control?

I had a neighbor kid having a rowdy party next door 6 months ago. The walls are 3 feet thick of brick but the sound system was powerful enough to make my apartment unusable whenever his parents were not home. But this one party was more obnoxious than most and at 4am on a work night I finally wired a large loop antenna against the common wall between my apartment and his and used my 100 watt transmitter to add a "little" RF to his mixer signal. It took 2 seconds for the system to be turned down after the blast of noise overpowered the sound source. A few minutes later, after the transmitter was unkeyed, the sound started up again so he got another blast. After 3 blasts, I've never heard his system again. Guitar amps have more gain and less shielding than hi-fi systems so are more impacted by RF sources.

[carl1987]

Thanks for the help fellas...but it is now happening at every place i try the amp at so I am going to say it has to do bad solder joints...not being close to an rf source. I took the back plate off the amp and everything looked pretty good...is there any possibility it can be old/bad tubes?

[km6xz]

It is not "bad solder joints", the catch all phrase techs use when they have not figured something out. It is not a tube, a failing tube very seldom increases in sensitivity to RF or the baseband modulation frequency. If anything picking up RF sources means the amp can amplify just fine, but the problem is almost always a problem that allows the amp to amplify the external signal that is being picked up by any one of a number of access routes. It can come in to the amp circuit by magnetic induction, rare however since the field drops off so fast as distance increases. It can come in by compromised shields at the input or any hi-z acces point. With amps with a lot of negative feedback...solid state amps...the speaker leads can be a good antenna. Bad cables and connectors are easy to identify...just unplug them and see if the interference goes away. Any effects loop units and cables are suspect as entry points. A change in position, antenna orientation or down-tilt of broadcast/amateur radio/public service transmitter etc tower can impact hearing now when before you didn't.
There are lots of thing to do to isolate the problem to the access point and treat that access point. What is done to treat it depends on what the nature or, and where it comes into the active high gain circuits of the amp. For example does the noise go away with any control changes and not with others? Which. Does shorting the input jack change anything, does shorting the guitar end of the cable do anything to the intereferrence? Does unplugging any series effects units(stomp boxes) from the amp input change anything. Any effects units plugged into the loop have effect? Speaker lead antennas can be bypassed by using a shielded dummy load and disconnecting the speakers...does it still react to RF?

[frankeg]

Not to discount what others have said but I've had bad pre-amp tubes that put out lots of static. It very well may be a bad tube. It's a simple subtitution job to find out. How long have you had/played the amp?

[carl1987]

i just tried the pencil tap test to my preamp tubes and one is absolutely "micro-phonic"...would replacing this be the solution?