CB radio

[wicked1]

I'm picking up CB radio on my amp. I did a search and found everything from "replace all tubes IMMEDIATELY or your amp will fry" to "Don't worry about it, it's common"

So, is it anything to worry about? If I don't have the ends of my interconnects plugged in to my preamp or dac I pick up very faint radio. As soon as a cable is plugged in to a grounded preamp, the slight radio noise goes away.
This CB radio comes in LOUD over the top of the music I'm listening to, but it's probably someone nearby w/ a little too much power in their CB tx.

This is in a pair of Ampex 620 monoblocks, which are 6v6 P.P.

thanks!

[DaveInVA]

I found the only way that really works in keeping out those pesky cabbage banders is to find the offending CB'er and push needles through his ant coax and cut the ends of the needles off. That will stop the interference...

Dave

[HollowState]

Originally posted by wicked1
but it's probably someone nearby w/ a little too much power in their CB tx.

Yea right! I've seen vehicles with several extra alternators hung on the engines and welding cables running back to amplifiers with a half dozen 8877s as finals.

[Miles Prower]

Originally posted by wicked1
So, is it anything to worry about? If I don't have the ends of my interconnects plugged in to my preamp or dac I pick up very faint radio. As soon as a cable is plugged in to a grounded preamp, the slight radio noise goes away.
This CB radio comes in LOUD over the top of the music I'm listening to, but it's probably someone nearby w/ a little too much power in their CB tx.

That is not good. The only way you could be hearing that radio is by means of detection. Detection means nonlinear. One or more stages of that amp are running in a nonlinear manner, and that's not helping the sonics one little bit. It could be a weak tube that's slipped towards cutoff enough to be functioning as a "plate detector", or it could just mean that the rig is close enough to be driving one or more stages into clipping. (In which case, a call to the FCC might be in order, but given the sad state of that ineffectual bureaucracy, the needle in the coax might get faster results.)

If it's coming in loud, then I'd take a look at the earliest stages for the fault. The detection is occurring up front and receiving substantial amplification.

[alexg]

Once I heard a CB radio on the public address system at LAX.

My cousin, who is into CB's uses those illegal CB boosters (don't know what they are called) and when he is parked in front of my house (when I still reside in Los Angeles), his CB conversation gets into my TV and into my audio equipment!

[Miles Prower]

Originally posted by alexg
My cousin, who is into CB's uses those illegal CB boosters (don't know what they are called) and when he is parked in front of my house (when I still reside in Los Angeles), his CB conversation gets into my TV and into my audio equipment!

They're called "linears", and most of the illegal ones (the FCC requires legit manufacturers of ham rigs to eliminate the possibility of retuning to the 11M band) are designed very badly. That's where your TV interferance comes from. Most of the VT-based designs eat tubes like corn flakes, which is why otherwise good audio finals like 6LW6s are so expen$ive. That's where all the NOS went since the big CB craze of the 1970s.

[Toobstheway]

Hey Wicked,
If you live very close to a major highway then you are pretty much left with trying to correct the problem within your amp. You cant stop all the truckers as a lot of them still run high power "linears". Now if you have a bucketmouth neighbor that is running illegal power just drop him a nice letter stating that you have recorded his conversation and if he doesn't stop you will submit the recorded proof to the FCC, that usually works. Trust me, I know as I have been on both ends of that issue. There is also the chance the guy may well be running within the legal limit of 4 watts but from some reason his CB is "washing" really bad. Washing meaning scattering stray unwanted RF.

[OzMikeH]

Originally posted by DaveInVA
I found the only way that really works in keeping out those pesky cabbage banders is to find the offending CB'er and push needles through his ant coax and cut the ends of the needles off. That will stop the interference...

Dave

I prefer putting the needles through the eyes.
I have nothing against ham freaks but morons causing problems with powerful hardware they installed just because they think it's cool need to be punished.
They are one step up from the idiots who shine laser pointers at landing aircraft.
If you are getting interference from an amateur radio operator they are almost always genuinely sorry for the trouble and will do what they can to stop the problem.

Shielded RCA cables will help. I figure they are a coaxial plug so you should use a coaxial cable. Many, many low and high end RCA cables aren't screened.

[w5jag]

Originally posted by wicked1


This CB radio comes in LOUD over the top of the music I'm listening to, but it's probably someone nearby w/ a little too much power in their CB tx.

This is in a pair of Ampex 620 monoblocks, which are 6v6 P.P.

thanks!

The easiest place for RF to get into your amp is the speaker leads acting as an antenna. A quarter wavelength at 11 meters is about 9 feet, so this length and multiples thereof should be avoided, and try to keep the speaker leads horizontally polarized rather than vertical, if your problem is in fact a CB'er.

A good start would be to try shielded speaker leads if your amp permits the shield to be grounded, and if that does not work, work backwards into the last stage of the amp looking for bad grounds, bad solder joints, etc., anything that can act as a rectifier.

Your statement that you also pick up RF with the line inputs open troubles me, but that's probably an unrelated problem to be fixed after you fix the CB problem.

Good luck,

Win W5JAG

[w5jag]

Another thing that occurs to me is that, if this is a "vintage" amp, one of the first things I do to any old piece of gear is to break loose EVERY ground conection in the device - tube sockets, terminal strips, I mean EVERYTHING, and put a drop of a good contact cleaner like DeOxit D5 between the chassis and whatever is fastened to it before it's tightened back up.

Flaky grounds can cause a lot of problems, and it's well within the realm of probablity that this can help your problem.

Win W5JAG