Mercury Magnetics Epiphone Valve JR Upgrade Kit Build Part Two

The re-soldering of the components to the main PCB is a fairly simple task, there is not too much that you need to be on the look out for. I had mentioned in part one that you will want an iron that has a variable temperature control; this really comes in handy when you are soldering the resistors and caps. You don’t want to overheat these components as you may damage them and degrade their performance. A high quality iron is one of the most important tools for this kind of work; it will make all the difference in the world in terms of ease of use and component damage. I also recommend that you look at getting some high quality solder. I use Cardas Quad Eutectic Solder and it is very easy to work with. This solder flows very quickly and has saved me many times from damaging components. The Cardas solder is a tin/lead/silver/copper mix and it is what I use for all of my cable and electronics projects.

Adding the resistors to the 6V6 tube socket is easy, but you will want to ensure that you have a pair of needle nose pliers. It can be tricky to navigate inside the chassis when you have the main board inside, and you’ll want to be extra careful that the iron tip doesn’t hit anything important! You might also notice that when the directions call for you to widen some of the holes on the PCB that the drill bit they call for may not widen out the hole enough. We found that some of the wires were a little too thick for some of the holes, so Phil ended up stepping up to the next bit for some extra wiggle room.

The center tap lead of the power transformer ends up being soldered to the underside of the main PCB board. The directions are not 100% clear on how to go about this, but with a little reading we found that you would need to scrape off some of the coating on the board till you get to the trace below it. For this part, you’ll need to go slowly and may not want to use the Dremel, as you will not want to cut or damage the trace below.

Once you have completed all of the steps on the board, it is helpful to double-check your work to make sure there are no cold solder joints or messy wires. This is the time to do any clean up on the board and neaten the wires. The directions include tips on making the interior nice and neat.  Again, stray wires can cause you an unbelievable amount of trouble. You may also want to verify continuity on the trace cuts and the new parts that you soldered.

The other piece of equipment you’re going to need for this modification is a Variac and if you don’t own one, you’ll need to borrow it. So why exactly do you need one? The variac will allow you to slowly bring the amplifier up to its operating voltage so you can monitor the amp using a voltmeter to ensure that everything is working correctly. In this case, we pulled the fuse and metered across the terminals to ensure the amplifier was maintaining its correct working voltage. Had the voltage gone past the correct level we could quickly and safely cut the power and not damage the amplifier. If there is an issue you will see the voltage spike well above the recommended level as you are turning the variac up. Also, if you happen to start smelling smoke as you turn the variac up then you’ll want to immediately kill the power and double check everything.

After we verified that the amplifier was working at the correct voltage it was time to plug in and turn it up! Right from the get go, you could tell that the Mercury Magnetics kit had brought new life into this little amp. The tone was immediately complex and rich, not loud or brutish, but smooth and inviting. There was also the immediate feeling of success; there is just an all around good feeling when you complete a project and hear it working for the first time.

Next up, the shootout!