Tweaking the GA40

mad dog

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Great fun this holiday weekend. Time for some further experiments with this tattered old tone monster. Had it running JJ 6v6s, with a Weber Cali paperdome ceramic speaker. And sounding very good too. But I kept reading about NOS tubes, and got curious about speakers. So picked up a set of NOS RCA 6v6s from the early 80s I guess, and a JBL D123 alnico speaker. The JBL was alleged to be a "holy grail" for low wattage amps, with "3D" clean.

First tried the tubes. As good as the JJs are, these RCAs are on another level. Definitely the right move. Then had to take the amp apart, pulled the baffle and replaced the speaker studs to fit the thicker framed JBL. All that trouble, and it didn't move me. Sounded good, but lost volume and bass. I could go for lower volume if the tone is right, but less bass is not good (IMHO 6v6s don't deliver the most solid bass to begin with..) With everything in pieces, I decided to see how the Cali would do in my Twilighter 260, which has two Cannabis Rex speakers. Loud, clear, smooth, but I keep looking for more mids and richness in that amp. Turns out that's exactly what the Cali delivers. (It's a rather warm tone I find.) Then, to complete the musical speakers game, put the CRex into the GA40.

BINGO. Game over. It's all the good stuff already in the amp, only louder, more clear. The Cali sounded good, but this CRex is way better. Especially with humbuckers, which can mush out in amps like this. I was getting these fat, gainy tones, early BB King maybe, every note right on the edge of feedback but still clear. The bass is tight, a huge improvement. What a cool amp!
 

capnjuan

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Hi Michael and congratulations on your 'musical speakers' exercise; always gratifying when you get it going your way. Just a comment on Gibson's policy of sparing every expense possible .... If you have the model with the decorative 'LP' script, this might not apply but if your baffleboard is like those in other Gibson amps, it's a sheet of 1/4" plywood with 1/4" X 1" or so plywood stiffeners around the edges; besides keeping the grillcloth off the baffle, the stiffeners help produce a better joint when the baffle is fastened to the cabinet.

I routinely replace baffleboards with 1/2", 9-ply, Baltic Birch plywood on eBay. If they don't need it when they come in the door, they will in the not-too-distant future. I don't so much get more bass; I get better bass - tighter, more articulate, crisper, snappier. If you mess up getting the old grillcloth off, the aftermarket has oxblood and oxblood/yellow stripe Gibson grillcloth. It's a pretty good piece of work but, for those of us who suffer from bouts of Obsessive Compulsive Disorder ... I also like to add a wiring strip using one of the output transformer bolt holes, terminate the output transformer leads on it, and then connect some #14 or #16 OFHC speaker wire for the speaker drop.

Mindless tweaking? Well ... maybe ... but Gibson wasn't a company to provide overbuilt output transformers and, over the years, the speaker drops, despite the insulation, will get a light coat of corrosion on the outside of the wiring. The outside is where the signal runs; not necessarily through the wire's cross-section. I agree that you can't do anything about the wire in the transformer's windings but they don't corrode and stiffen over the years like the drops. Anyway, for the effort I put in and for the not too much time and money it takes to replace the speaker feeds, I don't have to listen to the signal being pushed through two cheesey, slightly corroded #18 or #20 wires. I also think it produces a little more width and depth ... 'soundstage' as the 'Ophiles might call it. CJ
 

mad dog

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Cap: I certainly can see what you're saying on the wires. Why didn't I think of that?? The baffle is a touch flimsy for sure, not bad though. Wouldn't a full half inch thick baffle change the sound?

I guess this old character (the amp I mean) has a bit more tweaking in store ...
 

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mad dog

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Harsh maybe, true, certainly. Here's what I have. Pre speaker change. You'll have to imaging the Cannabis Rex in there:

GA40 front:
GA40_frontjpg.jpg


GA40 back:
GA40_backjpg.jpg


Beat but sweet detail:
GA40_front_lower_railjpg.jpg


The tweed actually flaps at the bottom on the sides, barely hanging on underneath. It's such a mojo rich old thing, I'm loath to change anything cosmetic. There may be some runic curse awaiting ill-considered actions. Plugging in reveals why it looks well-used, and puts cosmetics into perspective.

So I treat it with care. After all, it's almost as old as I am!!!

MD
 

capnjuan

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mad dog said:
The baffle is a touch flimsy for sure, not bad though. Wouldn't a full half inch thick baffle change the sound? I guess this old character (the amp I mean) has a bit more tweaking in store ...
Hi Michael: yes, it will change the sound; tighter, drier, woodier, less flubby bass. You are free to disagree but I approach these things with two thoughts in mind; first, as always, I wanna know if love is real .... and what would the amp sound like if some of the cost-driven manufacturing constraints were lifted. Said another way how, if at all, can the amp be altered to get the best possible sound without messing with its 'ampness'. In the pic below, a wiring strip has been added to the right of the new output transformer on my GA8 (threaded ad nauseum here); I later changed the strip to terminate the green/4ohm tap on the strip too. The speaker drops leading away are #16 oxygen-free, high-conductivity ... 'stereo'-grade stuff:

transformerdeck.jpg



This view shows a new Baltic birch baffleboard and 12" Weber (originally fitted with a 10"):

chassisviewnew02.jpg



The National Association of Really Cool Guys Who Buy and Sell Vintage Amps (NARCGWBSVA) has yet to publish standards and guidelines about the violability of vintage gear but I think it's worth keeping in mind that back in the day, Gibson was not only competing with Fender, each Gibson model was competing for its position in the product line. It wouldn't be in Gibson's interests to go all-out on the build standard for the GA8 for example because, if it sounded too good, it might interfere with sales of GA14s and likewise the de-tuned GA40 LP which they called the GA20T couldn't sound too good otherwise it might steal sales from the higher-margin GA40.

As far as I'm concerned, if cheesey 1/4" plywood baffles were such a good idea, then that's what Victoria, Clark, and the other boutiques would use; Gibson used them because they were the least-cost option and didn't add quality speaker extension cables and 12" speakers because they were building 'down' to a price-point, not 'up' to a quality standard. My GA8 was in very poor condition when I got it; now ... well ... I doubt there's another GA8 on the planet that sounds as good as mine. The poor as-received condition was an opportunity for me to apply boutique standards to a unique circuit and I have more in the tubeset than the amp cost new.

Having either a beater or a museum piece makes these decisions easier; if your amp is in average condition - whatever that is - then ... all that's left is deciding if you wanna know if love is real ... Best Wishes, John


Footnote: Loctite Household Repair to tab down the tolex ... J
 

mad dog

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[quote="capnjuanall that's left is deciding if you wanna know if love is real ... Best Wishes, John[/quote]

Cap: You truly have cut to the heart of the matter. I too would like to know ... IS LOVE REAL????

You're very right about comparative build quality, and about the wisdom of exploring logical mods to old gear. I'm already in violation with some purists just for appreciating high efficiency ceramic speakers -- or at least trying them -- in old tweed type amps. It doesn't always work, but is working in the GA40.

My concern with baffle swaps was not in the vintage correctness area, more wondering whether I'd gain something, but lose something else tonally by going that way. The stock baffle is actually rather nice. I do like the way the grill cloth is offset from the baffle wood. Great touch. The wood itself is dry, light, yet strong enough to carry the heavier ceramic speaker. So I'm wondering, maybe some of the great sound in this amp is in fact the cabinet size and construction, including baffle set-up? The only way to really see is to construct an alternate baffle ... do one with your specs, swap it in with the same speaker, see how it sounds.

That is an excellent idea. It would also give me an excuse to try something else, a 15" speaker. Always been curious how that would sound. Now I could pursue that, IN THE NAME OF LOVE (and science.)

Thanks for your thoughtful comment.s

MD
 

capnjuan

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mad dog said:
... I'm already in violation with some purists just for appreciating high efficiency ceramic speakers -- or at least trying them -- in old tweed type amps. It doesn't always work, but is working in the GA40.
I promise that I will not out you to NARCGWBSVA...
mad dog said:
My concern with baffle swaps ... wondering whether I'd gain something, but lose something else tonally ... It would also give me an excuse to try something else, a 15" speaker.
"What to leave in ... what to leave out.." Bob Seger Your amp will take a slightly larger sheet but still less than $40 delivered. Double-threaded speaker studs from Mojo here Mojo doesn't give the length of these; but if they are long enough, you can use them to bolt your baffleboard to the cabinet too ... would depend on the thickness of the batten. Ampwares (RIPenalServitude) used to carry the longer ones ... More likely than not, your original baffle uses a threaded 'nail'; flat head, threaded shaft, and those pesky flat washer nuts. If you can't find the double-threaded screws that are long enough, PM me with your street address. I have several old Gibson baffles (I keep them around to enhance my chances of membership in NARCGWBSVA); I'll take the fasteners out and send them to you. Grillcloth here, part # S-GSG1

mad dog said:
Now I could pursue that, IN THE NAME OF LOVE (and science.)
I note you have them in the correct sequence! Needless to say you have to check whether you have enough clearance for a 15" speaker; it may require lowering the center of the hole; can go as far as the lip of the speaker resting on the bottom batten; otherwise you have to cut the batten (frowned on at NARCGWBSVA; a GA8 is one thing, your amp ... that's another matter altogether). Good luck! J
 

mad dog

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John:

"Pesky" fasteners, man is that the truth! Homo Habilis here was stumped for a bit before solving the puzzle of how to get those off.

Thanks for the info, and for the links. Your help is much appreciated.

MD
 

capnjuan

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You must be referring to the little knucklebusters that hold the baffleboard to the cabinet ... I'm talking about these little pain-givers:

nutwasher.jpg



The litle flat washernut fastens the 'nail' to the baffleboard and keeps it from turning as the nut is tightened. These little Martins, short of splitting the wood, are near impossible to remove. I can't tell from the pics whether your baffleboard lays back from perpendicular. If so and if you mess with this, remember to tilt the blank back 10-15 deg from vertical and drill the holes level; that is, parallel to the ground. Otherwise no fit good. If I send you my mounting bolts, there will only be 8; the pics of your amp suggest 10 needed; 2 extra on the vertical dimension. J
 
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