REPAIRING MY FAVORITE GUITAR AMP OF ALL TIME! | 1956 Gibson GA-20T

In this video, we'll look at what I believe is the greatest vintage recording amp of all time. I have owned 3 amps with this exact circuit - two from 1959 and one from 1960. Every time I have sold one, I have regretted it and bought another one. This specimen is a 1956 Gibson GA-20T and it belongs to my friend, Steve Wilson, former touring amp tech for Stevie Ray Vaughn, Charlie Daniels, Greg Martin, etc. This model was later named "Ranger" when the Gibson cosmetics changed from two-tone to tweed in 1959-1961. This is the earliest iteration of this model, which featured a two-tone "oatmeal and buffalo hide" covering and was made between 1956-1957. It's one of only 338 made in 1956 and has dual channels and cathode-biased push-pull 6V6 output for about 12W, slamming an original Jensen P12R to its limit! Channel One sports a 12AY7 in the V1 slot with dual inputs each using one half of the tube. This channel has a deep, ballsy breakup which begs for double-stop blues bends. Channel One alone is probably good for a Top 10 spot on anyone's "Greatest" list, but Channel Two is what really sets this beast apart. This channel uses a 5879 pentode, which was far more commonly found in old reel to reel circuits of the day. The RCA Receiving Tube Manual has some example circuits utilizing this tube near the back of the book, and singles it out as a great circuit for hi-fi and microphone preamp applications. "Guitar Amp" is conspicuously absent in RCA's list of suggested applications, but obviously the Gibson designers knew something RCA didn't - that this tube would produce a PERFECT overdriven lead guitar tone in an era when "overdrive" was usually avoided at all costs. In fact, Gibson had made some obvious efforts to reduce this channel's overall gain and bass through the use of cascading high pass filters (HPFs) on Channel Two. They probably did this in order to help preserve the Jensen P12R and not receive a ton of returns of this amp for blown speakers. The HPFs used Sprague Bumblebee caps from the factory, which was probably an effort to use up old stock. In fact, the big brother to this amp - the GA-40T Les Paul - has BOTH channels using a 5879 tube in the first position, and Channel One omits these HPFs, using instead a single .01uf coupling cap. This delivered more bass and more gain to the upgraded Jensen P12Q speaker. Channel Two of the GA-20T Ranger also featured one of the best sounding tremolo circuits ever produced by Gibson, or anyone else for that matter. This circuit utilized a 6SQ7 octal oscillator tube - undoubtedly another attempt to use up old stock of this octal type tube at the factory. This oscillator produced a creamy tremolo that smoothly undulated in and out of tube saturation because it varied the bias on the 5879 pentode. While the GA-40T Les Paul amp had a bit higher gain and featured a larger cabinet and upgraded speaker with more power handling, the GA-20T has to take the cake as the better of the two for recording studio use. The full tube saturation begins to occur no matter which channel you're plugged into at around halfway up the dial and only gets more intense the more you crank it. The lower efficiency P12R has a magnificent cone breakup that perfectly compliments the tube overdrive. Humbuckers and P90s are particularly suited to this amp, which makes sense since it's a Gibson. The overall volume never rises to a painful level even fully cranked, and yet it can still somehow keep up in a blues or rock trio situation with bass and drums. This amp came to my bench with a non-working tremolo and possible issues with Channel Two. We'll repair all its issues and learn everything we can about this fascinating circuit. Then we'll play it with my Zio and 1952 Les Paul! STEVE'S CAVE OF GEAR: SRV's AMP TECH & His ALADDIN'S CAVE of GEAR! 1952 Gibson Les Paul: WTF!?! He's MODIFYING an ORIGINAL 1952 GIB... 1961 Gibson GA-20T Teardown & DEMO: 1961 Gibson Tweed Ranger GA-20T Teardown &... 1959 Epiphone Century EA-25T: Recapping Vintage Guitar Amps - When is "K... D-Lab GA-20T Repair: Vintage Gibson GA-20T Combo Tube guitar am... 1960 Gibson GA-20T: 1960 Gibson GA-20T Ranger Amp DEMO 1973 SG Special & Gibson GA-20T: HOLY GRAIL TONE! - 1959 Gibson GA-20T Rang... 1964 Supro Bermuda & Gibson GA-20T: HOLY GRAIL BLUES TONE 2 - Supro Bermuda & ... SHOW YOUR SUPPORT 1: Become a Member on Locals: https://theguitologist.locals.com/ 2: Donate via Paypal: https://paypal.me/guitologist?locale.... 3: Buy Merch: http://bit.ly/GuitologistMerch 4: Send in Viewer Mail. (Contact Me for details at [email protected]) 5: Purchase an ad! (Rate sheets available upon request at email above.) 6: Buy something from a sponsor and tell them I sent you. 7: Stand in the middle of the street naked screaming "LONG LIVE THE GUITOLOGIST!" Then when the cops arrive, tell them about my channel. 8: SUBSCRIBE TO THE FIXOLOGIST CHANNEL: @fixologist1