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Post subject: Vibro King Amp
Posted: Thu Nov 26, 2009 8:08 am
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I have been plagued with bad luck concerning the Vibro King amplifier. It has such a beautiful voice however, I have series issues with both the Vibro King amps I have owned. The first amp, was the fourth amp built and I am happy to say that fender stood by me when I pointed out a design flaw in the string that supported the reverb circuit. The next Vibro King, serial number 2517 is also a lemon. I have exhuasted every resource trying to remedy a thermal issue which results in a 'crackle' within minutes of use. I have explored different types of tubes, analyized the strings in the schematic, paid authorized fender repair shops to fix the problem, taken the amp to the amp tech's to the 'stars' and no-one can fix this problem. Has anyone else experienced these problems and found a solution? If so, I would greatly appreciate your advice. Thankyou. :shock:


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Posted: Thu Nov 26, 2009 11:14 pm
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Hi Mark, I'm an old guy amp tech, if it's OK I'd like to ask a couple of questions about the arcing noise. Does the noise occur consistently, so that every tech has been able to analyze it ? It happens only when a signal is applied, right, and if the amp has only been on for say 3 minutes, it will arc? Finally were all of the transformers(reverb and choke included) swapped out or hipot tested? When you say"string," you are talking about a circuit block or section of the amp, right? It's very curious to me that the arcing couldn't be isolated by the use of a scope or even the old transistor radio method. I've seen similar problems in '60s amps, where you could just touch them and cause an arc, yours isn't affected by any movements, right? ART

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Posted: Fri Nov 27, 2009 6:52 am
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Hi Art, Thanks so much for your interest and speedy reply. The 'arcing ' noise of the Vibro King seems to take a few minutes of playing before it begins. I believe all the amp techs have heard this noise and, finally a tech to the 'stars' pointed out resistorsand capacitors that he felt were too inferior to be part of the Vibro King and recommended an American brand of resistors by Sprague. Lastly, I am not certain wether or not the hotip procedure or transformer swaps were made however, I will inquire on Monday. Thansk again Art, much appreciated.
Kind Regards, Mark


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Posted: Sat Nov 28, 2009 8:07 pm
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Sorry to hear of your bad luck with these amps. I have had mine for 5 years and never had a single problem. The only noise I ever get is when I have the speed/intensity knobs in use, especially the intensity, and I can hear a pulsating noise when I am not playing. To me is sounds sort of like an arc type of noise. I'm sure mine is just a normal part of the vibrato. I think these amps are the best of the best. I Hope you get your issue figured out soon.

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Posted: Sat Nov 28, 2009 11:14 pm
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Hey Mark, the"inferior caps and resistors" were replaced, right? The hipot(high potential) transformer test is usually a last resort because of the cost, in the case of a newer amp, it's more expedient to replace the transformer. If the entire amp has been gone over thoroughly, then the transformers need to be checked by testing or substituion, whichever way is easiest and cost effective. I'm guessing the problem is more mundane, like caps, resistors, wiring, solder joints, or pots. ART

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