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Post by amishengine on Jun 26, 2008 10:02:29 GMT -7
I've got a late 90's Prescription Rx that I run through a Badcat Hotcat 2x12 cab mismatched with a Celestion Gold and a stock 25w Badcat speaker. In the last week or so the amp has become unbelievably muddy. With my Les Paul Classic the Rx now breaks up at even the lowest possible volumes ... as low as 0.5 and down. I have a little more headroom with my 52' tele, but even then the amp is dirty even below 1. The EL84's in the amp are only several months old, but I went ahead and replaced all of the power tubes with JJ's and swapped out the pre-amp tubes one by one, checking the amp in between each swap. No change. The amp still breaks up at painfully low volumes ... and it's not a pretty break-up. It's thick and muddy ... I had all of the circuits checked in the amp and everything matches up to specs ... so I'm completely lost. Any thoughts? I really love this amp - when it's clean. Right now it's killing me.
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Post by awesome on Jun 26, 2008 11:02:56 GMT -7
did you change the rectifier yet?
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Post by kruzty on Jun 26, 2008 11:21:17 GMT -7
It is my understanding that a rectifier tube works or it doesn't, so it probably isn't that. You said you swapped all the pre-amp tubes - does that include the EF86? Also, is it the same in the high and low input?
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Post by awesome on Jun 26, 2008 13:14:48 GMT -7
well thats probably true kruzty, didnt think about it.
a blown speaker could probably cause the distortion/muddiness. never had to experience it myself, but from what i've heard from others that sort of sounds like it.
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Post by awesome on Jun 29, 2008 14:50:34 GMT -7
i think that they can be biased but mainly for if the tubes run really hot or cold ( not for normal rated tubes)
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Post by ajnewkirk on Jun 29, 2008 23:47:46 GMT -7
Sounds like a possible speaker issue. I'd look at the speakers & wiring.
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Post by amishengine on Jun 30, 2008 20:54:08 GMT -7
Thanks for the speaker suggestion ... but that was the first thing I checked ... I hooked up my buddy's Maz 18 into my cab ... and she was clean as a whistle all the up, even with my LP. It's definitely something in the Rx ... I'm hoping just a biasing issue. I'm having my amp guy take a look at it when I'm home from tour next week ... just wanted to see if anyone had any suggestions while I'm on the road ... Thanks so much for the suggestions! Any help is highly appreciated ...
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Post by benttop (Steve) on Jun 30, 2008 21:02:39 GMT -7
I really doubt you have a biasing issue. Your amp is Cathode biased. For that reason the bias should always be perfect.
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Post by prsnstrat on Jul 1, 2008 7:05:51 GMT -7
I'd ship it to the Doc for a complete physical.
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Post by zane on Jul 1, 2008 7:06:17 GMT -7
I'd email the Doc.. or ask Myles in the "ask the experts" section...
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Post by Fiestared69 on Jul 1, 2008 7:56:56 GMT -7
I've got a late 90's Prescription Rx that I run through a Badcat Hotcat 2x12 cab mismatched with a Celestion Gold and a stock 25w Badcat speaker. In the last week or so the amp has become unbelievably muddy. With my Les Paul Classic the Rx now breaks up at even the lowest possible volumes ... as low as 0.5 and down. I have a little more headroom with my 52' tele, but even then the amp is dirty even below 1. The EL84's in the amp are only several months old, but I went ahead and replaced all of the power tubes with JJ's and swapped out the pre-amp tubes one by one, checking the amp in between each swap. No change. The amp still breaks up at painfully low volumes ... and it's not a pretty break-up. It's thick and muddy ... I had all of the circuits checked in the amp and everything matches up to specs ... so I'm completely lost. Any thoughts? I really love this amp - when it's clean. Right now it's killing me. Well If you have a late 90's Rx then you should not be running an EF86 as this amps preamp section is 3-12AX7's and that could be your problem!!
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Post by amishengine on Jul 11, 2008 6:03:24 GMT -7
I ended up swapping all three 12AX7 pre-amp tubes with 12TX7's (much lower-gain) ... this seemed to help significantly. When I plug into the Lo input channel the amp really sparkles and breaks up where it should ... I'm really happy with it now ... but this is obviously not a permanent fix ... any thoughts?
micah
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Post by Fiestared69 on Jul 11, 2008 7:14:22 GMT -7
If it is still breaking up to early I would look at your rectifier, depending on what you have in there some rectifiers will sag allowing and amp to break up sooner! you might try a cooper cap to stiffen it up a bit!
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Post by amishengine on Jul 11, 2008 14:25:03 GMT -7
thanks! i'll give that a whirl ... appreciate it!
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Post by Jim @94 Amps on Jul 14, 2008 21:13:16 GMT -7
You probably had/have a bad preamp tube or need a power tube refresh. Rectifiers usually work or don't work. Don't assume a new tube is a good tube when trying to trouble shoot bad tubes.
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Post by hdahs143 on Aug 27, 2008 22:11:20 GMT -7
If tubes didnt fix it, you may have a problem with the phase inverter circuit. Your amp tech should be able to fish that one out in no time.
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