Okay, this is weird. As I was pulling together notes (from back in the day), in order to logically discuss my initiation into the world of tube amp modification, I stumbled upon the fact that today is the anniversary of placing the winning bid of $125 for a Silvertone 1483--circa 1965. This fact was in a 2002 e-mail response from Steve Schneider, who planted the idea of snagging an amplifier with a little more oomph into my susceptible mind. I met Steve , way back in the day, through the Harp-L harmonica community and we had corresponded by e-mail a time or two about various topics of interest to the two of us. Eventually, we met in person when we both joined a chapter of the Harmonica Organization of Texas (H.O.O.T.). For me, Steve was the MVP of the chapter. He conducted valuable workshops on the inner workings of the harmonica and how to DIY with tunings, gapping, sealing, and anything else we'd could possibly want to know. Frequently, Steve would bring along one of his many vintage amplifiers and we would have great fun sucking and blowing through them. Then, Steve would get up and most of our jaws would drop during his exhibition of immaculate tone and mastery of amplified harmonica playing. He was the first harp player that I had met that actually owned a Sonny Jr. I.
Anyway--Steve tossed out a few amp choice ideas that I might consider in a move up the volume ladder, and possibly do so relatively inexpensively. He felt that a 1483 held promise as far as changing its stripes from a bass amplifier, that Sears and Roebuck called it, to a suitable mid-sized harp amp. I really didn't expect to win the ebay auction when I saw a candidate for consideration posted, especially since it was my first time to bid on the online site, but I did and Steve assured my that "I Too" could be my own amp tech.
This first ebay experience also gave me my first indication that there is a distinction between what I consider "works fine" means and an ebay seller's definition of the phrase. Since Steve was the proud owner of numerous vintage amplifiers and out of necessity began to study what makes them tick, or in some cases not tick, and how to optimize them for harp playing and since he was indirectly responsible for this purchase, I informed him to be careful with future advice because I expected him to hold my hand and guide me through the entire process of tweaking a vintage amp. And he did.
Between the time of placing the winning bid and the amp's arrival, I had to scurry around for a suitable cabinet of speakers since this 1483 deal was for the amplifier head only. The original incarnation of these amps had the head hardwired by a length of speaker cord to a cabinet with one 15" speaker. The amp head could conveniently be stored inside the speaker cabinet for transport. Fewer of those combinations are still intact due to the flimsy particle board construction of the cabs. A local music shop had an old Sunn combo amplifier with two 10" speakers and the owner only wanted the head out of it and agreed to sell me what was left for a very reasonable price, so I grabbed it, figuring that I could aways upgrade later. With that purchased, I only needed a blueprint to harp amp heave, so I scored a copy of a schematic online that I simply needed to print out--I realized quickly that it might as well had been in Greek.
The Silvertone arrived in excellent cosmetic shape for a piece of equipment almost four decades old. I followed Steve's advice and brought the amp up to power slowly with a homemade light bulb variac. When the time arrived for a test run, it proved to be a very disappointing moment and I thought, "Okay, so this is how this is going to go". A dull roar began to emanate from the amp and permeate the living room. Sounded pretty much like what my first amplifier sounded like when a power tube went south. So, I ordered and waited for a complete set of tubes instead of trying to figure out which individual one was the culprit. Since one of the tubes was actually labeled Silvertone, it indicated maybe that most of the tubes were original.
When the tubes arrived and were installed, I began the testing in earnest. I plugged in my Crystal Balls JT30 microphone (more on mics later) and began blowing and sucking the blues from channel one (the 1483 has two channels that mirror each other) and got a pretty darned loud tone going on. A little cleaner tone than I was looking for, but pretty darned loud. I put it through its paces and was liking what I heard, until I plugged into channel two which wasn't audible in the least. Bummer! But at least I had channel one to play around with, until further advice from Steve.
Steve offered possibilities for troubleshooting the problem and also turned me on to Don Destefano, who had assisted him a time or two. Don didn't really know why channel two would be dead, but also offered possibilities. None panned out. THEN as I poked around in the amp, attempting match up what I was seeing on the schematic with reality, I noticed a wire running from channel one to channel two that I couldn't find on the schematic. Steve lauded my discovery as a first step in understanding the importance of reading schematics. He suggested clipping the wire, which I did, and voila!--instant sound that was musical. Hey, maybe I could be an amp tech. I probably need to mention that Steve and I live no closer than 70 miles from each other and that most of his direction was taken over e-mail contact. I've got a sizeable book of those conversations printed out in a folder.
I told him that the amp didn't sound too bad as it was, but he insisted that we could do it better after hearing it at a H.O.O.T session and using it as a workshop topic--so we set out on that journey. Without going into great detail, I think I recall that the first move was to install new filter caps, then to replace the two prong power plug, fatten up the bass response with beefier coupling capacitors between gain stages, then we swapped out resistors to lower preamp voltages, fattened up and modified the inputs to have distinctly different channels, and re-biased the power tubes to run hotter for a warmer tone. Each of the mods were done incrementally and each one made the amp sound mo' better than before and I'd be ready to call it quits after each one. Steve had much better ears for amp tone critiques, so he would invite me out to where he was involved in assisting in running a fine jam session. He would plug my 1483 into his speaker cab, play a few rounds through it so I could hear it myself, tape me playing through it, comment on the fact that it was a worthy harp amp specimen, and then send me back to the drawing board to improve it even better. I had to work the mod tweaks and scheduling time to get over to the jam with the preoccupation of making a living, so time would lapse between "live" test runs. We kept at this well over a year, maybe going on two, and the amplifier improved in the tone department with each mod suggestion. Today, I think it would match up favorably with quite a few good harp amps today. Of course, I haven't mentioned that the Sunn cabinet speakers basically sucked, so I'll have to post about exactly what I had to do in that department and the story of "The Python", that is pictured at the top of this post.
By Request These Are Some of the 1483 Mods:
Coupling capacitors C17 and C18-- .1mfd Orange drops
Channel Two input to grid leak--5meg resistor with a .022uf cap in series
R41 & R24--3.3k for each
Cathode Bias Resistor--180ohm to warm up the 6L6s