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Radio interference mod RP-65

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Chris Cohade (chrisco)
Username: chrisco

Registered: 07-2010
Posted on Thursday, July 29, 2010 - 06:49 pm:   

Hi, I'm new here. I bought a 112RP65 for $75 at a flea market last year and it works. I need a cap job (fuzz/fizz when using the high gain input). The main problem is I get lots of radio interference when the reverb is turned on or the gain turned up. Very little with gain and reverb on zero. I saw the musicman service bulletin #5 here, which has a simple mod and suggests replacing some LM1458N ICs with LF353Ns. Just wondering if anyone has done this and if it changes the sound of the amp? I see the 6L6 version of the amp has several LF353Ns already, mine is a 6CA7 model (I've got JJ KT-77s in it though.)
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Thursday, July 29, 2010 - 10:01 pm:   

Kool another kt user ! the service bulletin shouldn't change the sound,it's basically just using shielding and grounding to cure the prob .i only get abit of noise from mine (100rd) when the tv is on .i have not yet done the mod though.
Chris Cohade (chrisco)
Username: chrisco

Registered: 07-2010
Posted on Friday, July 30, 2010 - 09:54 pm:   

Thanks for the reply Bill. Would changing some of the ICs from LM1458N LF353Ns affect the sound? The bulletin says the 353s don't pick up radio. I live in San Francisco close to the radio towers and I'm picking up music sometimes. Also will this require other changes in the circuit because of changed values?
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Friday, July 30, 2010 - 11:03 pm:   

well, actually i've never tried the 353's,but there are many substitutes today for the 1458,some can thin a sound abit thin,but most you'll never hear a difference.theres a thread on here about good substitutes for the 1458 check it out .but i would have to believe most all ics made today combat rf.
Bill Traylor (bozzy369)
Username: bozzy369

Registered: 02-2008
Posted on Friday, July 30, 2010 - 11:06 pm:   

go to:Solid State Devices & Substitutions
look around in there lots of info.