Monthly Archives: March 2014

Installing the Circuit Board and Completion.

With the leads all wired the next step was to drop in the board and wire it to the tube sockets, potentiometers, and transformers. This was time consuming for me as I have raging O.C.D. so every wire must be just right. I took my time and I am happy with the lead dress.

*** WARNING – THE VOLTAGES INSIDE OF A GUITAR AMP CAN KILL YOU! Even adfter the amp is unplugged the capacitors can store lethal voltage. Learn how to drain caps by clicking here.***

I did some preliminary voltage testing as described in the Metroamp 50 Watt Kit Instructions. My voltages were slightly different because of the transformers and layout I was using, but I found correct voltages on the internet. Everything looked good. With a speaker attached, I biased the power tubes to 40ma as suggested by Chris Merren.

Now the final moment – I plugged in my hot rodded Tele and flipped the standby switch. The amp came to life. What a great St. Patrick’s day present! I goofed around a little with the amp and the tone is unreal with a beautiful aggressive and full crunchy sound. I let it burn in for a while, hitting a chord every now and then.

But all is not perfect in paradise. I noticed the amp has a slight hum even when no guitar is plugged in or even if the master volume is turned down. It is almost too small to complain about, but this is to be the keeper amp of my life. I must track down the source of the hum to make the amp perfect.

Yes, I know I am nuts.

I will do some research and hit the forums for some ideas.

Stay tuned.

 

Adding Wire Leads to the Circuit board

Soldered the components to the turret board before adding the wire leads. This is actually the incorrect order of normal wiring as soldering the leads to the turrets can introduce heat into the resistors and caps possibly damaging them. I encourage you to wire the leads first and then mount the resistors and caps. Since it was too late for me to do this, I clipped an alligator clip to each component just above the solder joint to act as a heat sink and dissipate the heat away from the component. It worked well because when I felt the components right after soldering they were hardly warm to the touch. I like to solder using very high heat. Around 750 degrees on my Weller WESD51 digital readout soldering iron. The idea to to get in and get out quickly so the heat does not have time to spread to other parts of the circuit.

I used a pair of standoffs on the mounting holes to provide a stand for the board when working on it so the component leads would not get bent.

I used 22AWG PTFE wire and left the tails slightly longer than normal.

*** NOTE – I later changed all of the wire to a thicker 20AWG. This wire holds its form better when bending and may provide increased signal flow. I also later routed the wire through the perfboard and soldered the wires on the top of the board by wrapping them around the lower portion of the turrets. This was done for two reasons: strain relief (prevents the wires from breaking when pulling on them during assembly) and the ability to see the wire actually connected to the solder point. ***