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Vintage threads from the first ten years

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Radio interference

3/11/1998 7:22 PM
Peter Festejo
Radio interference
Hey guys! I need your help!!! Earlier today I was in a studio laying down some guitar parts with my  
Matchless HC-30 head/2x12 Matchless cab. The problem however was that I was getting serious radio  
interference from the amp. I tried using different outlets, moving the amp around in the room etc. but none  
of these things helped at all. Is there anything I can do to avoid this extremely annoying problem or is this a  
function of the guitar or room itself (wall outlets, light fixtures, various electrical cables, etc.)? The  
interference became even louder and more noticeable when I switched my TS9 and Deja Vibe on. I usually  
get a small amount of interference in our rehearsal room as well but not at any disturbing levels. Are tube  
amps more susceptible/sensitive to this phenomenen than solid-state amps? While I'm on the subject, can  
anyone please recommend some good speakers to replace the ones in my Matchless 2x12 cab? I find the  
stock ones a bit too flabby/muddy in the bass and they seem to break up a bit too  
soon for my liking.I would like a little more headroom, a tighter bass response as well as sweet/smooth  
distortion characteristics. Any suggestions? All help and info appreciated greatly!!!!  
3/12/1998 2:53 AM
I don't know a lot but i got rid of a lot of radio interference in my old tube amp with new cords and the rest was cleaned up with a three prong plug installation.  
I live near the local tv and radio transmitter hill.  
You must have good cords and a mordern wall plug.  
3/12/1998 2:49 PM
To get rid of the radio interference you might  
try putting a small cap (100 pF or so) from the  
first input grid to ground.  
3/12/1998 4:02 PM

Maybe he has "too good" cord ,because it has not enough capacitance to block RF interference to ground ;-)  
3/12/1998 4:27 PM

Sometimes a poor solder joint in the right location will act like a semiconductor diode junction, and operate as an AM detector.  
This could be anywhere from the winding/eyelet connection on a pickup to the connecting cord.  
3/12/1998 10:35 PM

You might want to try to find a  
copy of Jack Darr's book Electric  
Guitar Amplifier Handbook.There is  
some good information on eliminating  
RFI in one of the chapters.
3/13/1998 2:55 PM
Steve M.

Just to expand a little on D.H.'s suggestion: one excellent (and cheap) way to get old out of print materials is to go to your local public library and ask for the book via Interlibrary Loan. You should have as much information on the book as possible to make the book easy to find. I've had good luck in getting both the 1st and 3rd editions of Jack Darr's book, the RDH4, and several old out of print hifi manuals. When I get the books, I usually photocopy them, which technically is illegal, but I believe that preserving access to information is more important than following outdated copyright laws that have not kept up with the times, but I digress.  
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