Here is a link to the raw scan :  4 Meg PNG

And one in a more palatable 290K size

Smaller but very decent GA-5 Crestline Schematic

So where to begin? The first thing is details. This schematic is full of details that I have not seen on GA5 schematics before. Some are trivial (it includes part numbers) and others are very useful (the output tranny is 8k/8 Ω).

Secondly, topology. This amp is significantly different in some design details.

Third, local interest. This is GA-5 but the topology matches my GA-5T, so I have a better idea of what was original in the amp that I have on the rack at this moment.

I have slurped every GA-5 Schematic I could find and I don’t think I’ve ever come across one like this, so I am kind of excited to show this. Naturally, it is my scan of a very old document. This image is in the public domain. I didn’t even watermark it.

Enjoy, and I’ll be commenting further on the details shortly.

Skylark Faceplate with plenty of rust (click for fullsize image)

Now it’s not going to matter one bit if I don’t do anything about the looks, but it would be nice to get her cleaned up. There is no way I am going to be able to clean around the silk-screened lettering or lines. So the whole thing is going to have to come off. I don’t even know how you clean these things.

Now, the chassis is actually just a single piece of metal, bent and punched. I’m not sure if it’s steel or aluminum but either way, it’s easily bendable.
Here is a picture of one out of the cabinet :

5T Chassis out of cabinet and looking from behind

So I suppose I could just have one remade. That would surely cost more than the amp, but I’d come out of it with the specs for new metal, which would be a good thing for anyone else trying to do this. Then I would need to get the art redone or redesign something. Again.. favors or money and no improvement in the sound.

I’m leaning towards leaving it, for obvious reasons, but very early in the process I’ll have to make the decision.. anyone have any thoughts?

This is a Gibson Skylark in the “Crestline” series.  It is one of the many amps released with the GA-5T model number.   This was made sometime in the early 60′s as the later model “Whiteface” amps would be released in ’65.   This is not as popular as the true Class A SE Skylarks from the 50′s so it cost me $202.50 with shipping a couple of years back.  It’s not working right now and I’ve decided to refurb it.

When it worked (which it actually did at some point) it had the best tremolo I had ever heard.   It is so weird that Gibson tremolo is the shame of high end amp world these days.  They used to do it brilliantly.   However, I don’t like trem, so it’s going out..  in it’s place is a Master Volume.   I’ve read all the gasbags saying “It’s not the same!  You won’t get .. “  but the truth is I don’t care.  It makes a good sound.   If I get a different sound from 11 on both dials, great!  That’s just more versatility to me.

Here is the plan in general :

• Use the original  Iron, Speaker, Cabinet and Chassis as much as possible
• Mod back to original GA-5 specs, removing tremolo circuit.   except as noted below.
• Replace all discretes using original bone stock values
• Add Standby switch (hopefully I can do this with a rotary switch like they have now)
• Use multiple parallel caps for filtering ( a la TUT5)
• Add Master Volume before the Phase Splitter
• Add Pentode/Triode/Other switch
  • Pentode – Standard operation except provide 1k flameproof resistor for each screen
  • Triode – Put the screen in the plate loop (keeping the 1k resistors)
  • Other – Lower the voltage supplied to the screen (should be something between the other two in terms of breakup)
• “Galaxy” grounding, again, a la TUT5
• Careful layout and use of shielded wire on the signal path.

Should really be doable in a weekend if I have the parts, but I really want to nail this build, so I’ll take my time.