There are few things that make a gear heads heart skip a beat like the two words “vintage gear”. There is something about the sounds, smell and appearances of musical equipment of yester-year that make us feel giddy and nostalgic. So when my friend and long- time client Paul Feltman contacted me, I knew something cool was coming my way.
Paul who is the guitarist and founding member of the band “The 18 Wheelers” (www.18wheelers.org) is a huge vintage gear fanatic and collector of vintage guitars. His collection ranges from Telecasters, to Les Pauls and everything in between, including a pretty retro Sears Silvertone with original amp case and a 80s Van Halen Charvel replica. Paul had been holding onto a 1953 Gibson GA-20 amplifier for some time waiting for someone to get it back into functioning order. The amp had been purchased along with a 1960s ES-330 and had been previously serviced rather poorly. Paul contacted me and we went ahead and got her sounding like she deserved. Follow me in my journey as I restore a legend and piece of history.
The Gibson GA-20 was produced in various configurations between 1950 and 1961. Our specific model was advertised producing 12-14 watts powered by two 6V6 tubes in the power section, and two 6SJ7 tubes in the preamp section. The rectifier section houses a 5Y3 while the phase inverter is a 6SL7. The speaker is a Jensen p12r which sounds nice and twangy on a single coil pick up, and thick and creamy on a humbucker. The sound this amp produces inspires a guitarist to run nothing between it and their guitar except a cable to link the two. The GA-20 isthe sound I hear in my head when someone refers to vintage amp tone. It overdrives easily and breaks up exactly where you want it to. Add a little reverb and like Paul says, you enter tone heaven.
After making arrangements with Paul I brought her home and quickly began diagnosing issues. The initial look over left me speechless. There were wires everywhere! Caps had been moved around, resistors were bloated and the original filter caps had been replaced with newer Sprague atom caps, and even that had been twenty years ago. This poor little amp was in despair and in need of some serious tender love and care. I pulled my fluke meter and scope out and began tracing components in the schematic. I quickly discovered a few things. The first of the problems was that the previous tech had pretty much wired a separate input into the amp and tried to bypass the input jacks all together. I don’t understand why, as the original inputs worked just fine, regardless of capacitor and tube degradation. I removed the input he installed and excess wire and when ahead and slowly powered her up with a Variac. Low and behold we had a sound! You could tell she needed service, but she was functioning properly.
I went ahead and measured capacitance on the removed filter caps and noticed they had floated. I repeated the procedure with every cap, and resistor in the amp. After determining what had to be replaced I made a list. All the filter caps were replaced with new Sprague atom caps, along with many of the carbon resistors that had bloated and cracked. The cataloging was tedious, but well worth it. The original grey tiger tone caps were replaced with proper value Mallory caps, which were scoped and measured to be installed in the correct orientation. The original Jensen p12r was removed and stored carefully and replaced with a reproduction p12r from none other than Jensen. The potentiometers were carefully cleaned, along with all the inputs. The output transformer was tested, and confirmed was working correctly. The output transformer was also relocated beside the new speaker as opposed to being mounted right on the speaker. All the burnt out tubes were replaced with new old stock, except the power tubes which we replaced with Mullard 6V6 units. For safety reasons we went ahead and replaced the 2 prong power cord with a modern 3 prong grounded cord. To add the finishing touch, we had a new leather handle and mounted it using brass screws which will age as gracefully as every other component had.
With all the components in place and grounding double checked, we plugged our little GA20 into a Variac and slowly powered it up. As expected there was not a single issue. She powered right up, and as soon as those tubes warmed up we were in “tone heaven”. The clean sounds were bright and chimey, the overdriven break up sounded like something right off a 50s record, and everything we did to it surprised us further and further. We had resurrected a living legend. This amplifier which had been produced over sixty years ago was alive and well. We called Paul up and arranged delivery. As soon as he plugged it in and heard what came out a huge grin took over his face. He looked at me and said “man, what a great tone”. Those four words are always enough to justify my hard work and attention to detail.