Egnater Tweaker 40 Power Transformer Problems

April 04, 2014

The Egnater Tweaker 40 is a cool little tube amp with a huge amount of flexibility in the tonal options available.  The front panel is full of switches that change the functionality of the other controls and really offer a wide palette of tonal options for the adventurous guitarist.

All of this is great, however, we have been seeing a fair number of power transformer failures in these and not due to the typical situations of operator putting in too large of a fuse or other typical transformer failure scenarios.  In fact our latest experience involved a unit that would only intermittently blow the fuse and a strange 'crackling' sound that was not always accompanying the fuse failures.  After further inspection we found an intermittent short in the transformer windings making a transformer swap necessary.  We are seeing these kinds of transformer issues more frequently among those products that utilize parts sourced from certain overseas countries known for 'low prices'.

It is our preference in these cases to go ahead and put in some real quality parts and in this case that meant slapping in a Mercury Magnetics transformer. This is a definite upgrade and Made In The USA!!  Mercury transformers are built rock solid and have always produced a tonal improvement every time we have used them.  For this reason we use them frequently and feature them in many of our custom builds as well.

Due to the way the transformer is mounted and some heat related issues from the arcing coming from the transformer, we needed to remove the front PCB assembly for some additional room to work and some necessary repairs to the solder joints.  The old transformer was removed to prep for installation of the new transformer.

The design of this amplifier necessitates the use of a transformer with multiple primaries as well as multiple secondary windings so it is important to understand the wiring as well as make sure that the amplifier schematic and transformer diagram are verified to have matching color codes. As is sometimes the case there are slight variations and the appropriate changes were implemented for proper and safe operation.

Due to the large number of wires and the tight space constraints it was imperative to pay close attention to wire routing and bundling in order to make sure everything fit and just as important wire routing can have a huge effect on the overall noise level of the amplifier.  As with the original transformer we installed heavy duty heat shrink sleeves to the bundles where they were routed through the chassis for protection and a neat finished look. These wires all had to be terminated with spade connectors and bundled to be routed to the proper locations in 'harnesses'. 

Once everything was hooked up with circuit board reinstalled, the unit was given a proper bench test including bringing up power on a variable AC supply to safely and properly verify all circuit voltages.  New tubes were installed at this point and the output tube bias was adjusted for proper calibration.  After verifying operation with a signal generator and scope it is time for the fun to begin.  The amp was put through its proper paces with all functions tested by playing guitar through it into a Marshall 412 cabinet.  Another problem solved and another great result from Mercury Transformers.