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Posted: Mon Sep 14, 2009 6:40 pm
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Joined: Mon Sep 14, 2009 6:08 pm
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Sorry guys, this is a question i have about my hrdx. I have read that some of you guys hate this amp. I am beginning to see why. I have a 96 amp, very road worn. I bought it used about 6 mths ago. It started to have a crackle about a month ago. Shortly after that, I had a lack of volume and very knarly fuzz on the clean channel. I noticed it at low volume at first. It also has a pretty good hum on the drive and more drive channels. This being my first tube amp I thought it was just normal. I found Justins site and realized that this is a pretty common thing. Being pretty handy with a vmm and solder gun I found and replaced an open 82 k resistor on the valve board. ( I believe it was r57) This did help with the fuzz I was getting, but the crackle was still there. It seems like it comes up after the amp warms for about 10 minutes or so. I did replace the 2 - 5 watt 470 ohm resistors, off the board, to no avail. I was checking some voltages at the 3.3 volt power transformer input on the valve board. I am not sure but I believe I may have shorted those 2 together when I was checking the voltages. It gave me an imediate feedback voltage sound through the speaker. I shut it down. Now, when I turn it on, it gives me this major feed back type sound after about 5 minutes. The sound is almost like an open ended jack that is plugged in to the amp and you are touching with your hand on the other. only MUCH louder. Any help would be MUCH appreciated. I am sorry to be so long winded, I just wanted to give you guys all the facts for a good educated guess.


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Posted: Mon Sep 14, 2009 7:27 pm
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Joined: Fri Jan 02, 2009 3:17 pm
Posts: 1986
You might find your answer here , but if not you might want to post on the fender discussion page at the "amp, mods, repairs and projects" section .There are people there that repair amps for a living. I know there is a guy there named willie who is very knowledgeable and others too who are quite helpful.Good luck.


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Posted: Mon Sep 14, 2009 9:05 pm
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Joined: Fri Jun 26, 2009 6:53 pm
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Location: Harvard IL
Yeah, Bigdaddy sounds like positive feedback. Don't know which component you refer to concerning a 3.3 volt power trans input. But I work on the older amps. If you're talking about the 6.3 filament heater circuit off the power trans, then I would pull out all the tubes and check that you are getting about 6.3 ACvolts at the filament pins on each socket. If the valves are mounted to the board, I would check all the traces for continuity and make a visual inspection. With some luck, you just toasted a tube. The fact that it takes 5min to produce the feedback is interesting. Good Luck! ART


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Posted: Tue Sep 15, 2009 5:56 am
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Joined: Tue Jan 27, 2009 3:41 pm
Posts: 1257
The best source of amp information ont he web is The Fender Forum (not to be confused with the FDP). There are several guys there who are not just tinkerers or kit-builders, but people who can actually design a circuit... look for answers for the guys who call themselves "Kap'n" and "NTBluesGuitar." They are the real deal.

http://www.thefenderforum.com/


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