Last Centerfold Of Skylark Circuitry

6 10 2008

With this last photo of the GA-5T’s circuitry, it’s time to move onto another dusty old amp.

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Skylark vs. Champ?

22 09 2008

I’ve run across many references of the GA-5/GA-5T being billed as Gibson’s answer to the Fender Champ, but with so many versions of both to consider, that’s a hard statement to reconcile. As far as this version of that Gibson amp is concerned, the Skylark has completely different tubes than any of the Champs and while the circuitry is a bit similar here and there to some of the Fenders, it’s different enough to distance the two. Here’s more photos of the Skylark’s guts.





More Skylark Circuitry Photos

14 09 2008

New capacitors mingle with old resistors amid 42 year old wires coming from the power transformer.





Skylark: Taking Off Her Top

9 09 2008

Pulling out the chassis, the Skylark is one clean machine internally. It’s a pretty basic circuit with crisp connections and logical layout on a small, thin eyelet board. No transistors, no integrated circuits, just resistors and capacitors wired beautifully point to point, the way nature intended for guitar amplifiers.





If It’s Valves You’ve Come For…

6 08 2008

The 6BQ5, also known by it’s European designation of EL-84, is renowned as one of the most prized tubes among amp designers and it’s characteristically sweet tone is the foundation of the Skylark’s sound. The other valves in this amp aren’t so familiar. The 6EU7, which Gibson used a fair bit in different 1960’s tube amps, is a low noise alternative to the more commonplace 12AX7 but the two preamp valves are of equal gain values and overall are ,very similar. The 6C4 tube was used in many applications, such as organs, ham radios and even TVs but Gibson used them in amps as either rectifiers or in this case, a phase inverter.





It’s All About The Glass

5 08 2008
gibson-ga-5t-9

As can be seen here with the photo turned upside down, there are four tubes in the Skylark; a pair of 6BQ5, a 6C4 and a 6EU7. Going from left to right, the 6EU7 serves as the power tube and its faint red RCA marking is barely legible. Next is the phase inverter, a 6C4 bearing the yellow script “made in USA for Ampeg by Sylvania 939 JFO”. The first 6BQ5 in the lineup sports the “RCA electron tube” marking while its partner 6BQ5 makes do with “RCA USA”. The tubes are old but after warming up a bit, still kick out a toneful 4 or 5 watts.





A Peek Under The Skirt

4 08 2008

 

 

 

 

 

 

 

 

 

The Skylark is a pretty clean machine under the bonnet; four tubes, three pieces of iron, an old tremelo switch footpedal and big ol’ 10 inch generic speaker. The power transformer is a bit rusty but looks original? Stamped on it is the sequence “TF-105-P 9966606”. The output transformer bears “TF-504-0 549-6538” while the choke is branded “TF-1001 D 757 6549”.  The underside of the chassis has “insp by 152246” printed on it with the “15” being larger than the following numbers.