Home Up AMPEG SVP-Pro AudioTronics Carvin DMX MX3282A eDrum kit



This is an instrument tube preamp utilizing four (4) 12AX7s and one 12AU7 tube.

We think it has an intermittent something some where inside.  It cuts out in the middle of a set.  Usually the third or last set of the night.  Just enough to ruin any trust in this pre-amp.  So it I took a look at it for my good friend a bass player.  

After burning this unit for many hours over many days and tapping around the unit I observed two possible intermittent items.  The power cord receptacle on the rear chassis or the female plug end or the front panel input jack.  The power did not come on when I first plugged in the rear power cord connector.  I fussed with it for a minute then it has not failed since. The other possibility was a dirty 1/4 inch front panel input jack.

I cleaned all the connectors and pots.  Then I set about testing the tubes on a Hickok tube tester.  All tube tested good and above GM spec.  

I decided to replace the input and two output connectors.  They get the most abuse.  I do not like the weak tin material they are made of.  I suppose the original plastic and tin made for easy installations.  But I prefer the good old silver plated heavy duty (commercial grade) Switchcraft connectors. 

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This suspected jack was cleaned with De-Oxit and resoldered. 
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The new input jack
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Wired and installed. 
IMPORTANT NOTE.  Use a short cover screw.  The original shorted to the phone jack solder tab.  
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New Output jacks insulated with ACE Hardware fiber washers and O ring (not seen) to center the connector in the panel hole.
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New output jacks wired in with high temperature & voltage stranded Teflon coated wire. 
These are Switchcraft Silver plated commercial grade jacks.   The input jack is number 502-14B 3 conductor 1/4" phone.  The output are 502-11, two conductor phone. Don't forget the insulating washers for the output connectors. 
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Board interconnections resoldered. 
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Any high stress joint was resoldered. 
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I am listening to this pre-amp as I update this page.  I have an FM radio as the input source and amplified computer speaker as the output. Not the best acoustic response but good enough for a long hard burn-in!
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All other controls and the rear AC power receptacle have been cleaned and lubed with De-Oxit. 
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Tube test results.  The 2nd to last column is the the Cathode activity test with a reduced heater voltage. 
The last column is the minimum GM to be good.
All tubes passed. 

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