Here is my GA40 build...check this bad boy out

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fzfwyv
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Joined: Tue Mar 07, 2006 10:37 pm

Here is my GA40 build...check this bad boy out

Post by fzfwyv »

Well...here it is and it rocks.

First off, I know it looks like a rats nest in there, but I put this thing together carefully, in sections, and this amp is quiet as shit! I mean hardly noticiable nosie floor even with both of those 5879's in there.

The build follows the schedmatic pretty close. I did my own layout from the schem. I know it doesn't look organized but it is. A few minor tweaks...on channel 1 I added a 3 position bypass switch to alter the "contour"...basically fat to thin. I also added a jack and switch for the trem. I have a simple on/off footswitch I plug in there to turn the trem on or off.

And the trem...WOW! It's great, it's lush and there's no freaking thump or noise...how cool is that!

I only have two inputs, one for each channel. I can use an A/B box and plug into both at the same time which is really cool too. I like this amp quite a bit...no mush or flub.

You can get some clean on the trem channel, which sounds a little more crisp than the normal channel. Both have their unique tone.

I had some work tweaking the voltages. Channel 2 (Trem) is spot on to the GA40 voltages. Channel 1 is lowered more than the GA40 down to Divided by 13 FTR 37 voltages...makes channel 1 sing.

I recommend this as another great option for a low watt build

here's the pics:

[img:1306:980]http://mywebpages.comcast.net/rszmagaj/ga40_1.jpg[/img]

[img:1306:980]http://mywebpages.comcast.net/rszmagaj/ga40_2.jpg[/img]

[img:1306:980]http://mywebpages.comcast.net/rszmagaj/ga40_3.jpg[/img]

[img:1306:980]http://mywebpages.comcast.net/rszmagaj/ga40_4.jpg[/img]

[img:1306:980]http://mywebpages.comcast.net/rszmagaj/ga40_5.jpg[/img]


-Rich
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Colossal
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Re: Here is my GA40 build...check this bad boy out

Post by Colossal »

Really cool Rich! I'll bet it sounds great. Nice choice of components. Top notch!
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M Fowler
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Re: Here is my GA40 build...check this bad boy out

Post by M Fowler »

I like it nice work to my eyes. I do enjoy the PTP builds though. :)
phalanges
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Re: Here is my GA40 build...check this bad boy out

Post by phalanges »

That's a beautiful bit of component sculpture.
Congrat's
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KT66
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Re: Here is my GA40 build...check this bad boy out

Post by KT66 »

Nice job Rich, not a rats nest at all - and the PTP is cool. Why only 2 Jupiters - only on one channel ? Looks like the resistors are the mil spec ones from Westlabs and that's a Plexi chassis, right ?
Ryan

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http://Classictubeamps.com
paulster
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Re: Here is my GA40 build...check this bad boy out

Post by paulster »

Are they the PRP GP1 resistors or the PR9372 audio grade ones? Both look the same.

I love the GP1s but haven't tried the PR9372s yet.

Nice build. Like it a lot.
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daydreamer
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Re: Here is my GA40 build...check this bad boy out

Post by daydreamer »

WOW. what a beautiful amp.

I'm starting to look at designs for a first build, and I notice the transformers on each design are arranged differently.

Are those transformers arranged like that for convenience or for a more technical reason (noise suppression or something)?

What do you attribute the absence of noise in your build? This is probably the single biggest thing I'm looking for.
"Too young to know, too old to listen..."

Suze Demachi- Baby Animals
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Structo
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Re: Here is my GA40 build...check this bad boy out

Post by Structo »

Nice looking amp.

Now you need a nice combo cab with a 12" Jensen or similar.


What is the orange electrolytic cap on the filter board?
Tom

Don't let that smoke out!
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KindaFuzzy
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Re: Here is my GA40 build...check this bad boy out

Post by KindaFuzzy »

I really liked the ga-40 circuit when I built one for a friend. On mine the tremolo got kind of weak as you turned the volume up though, so I used the 6sq7 as a mixer with local feedback, and rewired the trem channel 5879 to be a bit brighter and thinner sounding. It worked out well, especially when the channels were jumpered.

How do you like the sound of the input choke?
fzfwyv
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Re: Here is my GA40 build...check this bad boy out

Post by fzfwyv »

KT66 wrote:Nice job Rich, not a rats nest at all - and the PTP is cool. Why only 2 Jupiters - only on one channel ? Looks like the resistors are the mil spec ones from Westlabs and that's a Plexi chassis, right ?
The Jupiters are used in the PI, I figured I'd give them a shot. Honestly I can't say whether thay make a difference but maybe one doay I'll do an all CC resistor/Jupiter cap build. It would be interesting.

Yep, they are mostly PRP resistors, 1watt. Some are 1/2 watt. I've done builds with them before and think they are a good mix of tone and tight-tolerance, low noise resistor.

I mounted the trannies based on the chassis. It was a Weber chassis and I had to drill a few extra holes to accomodate the trem tube and one of the 5879 tubes.

I think they combination of resistors and getting lucky on a grounding scheme keeps the noise level really low. That's one thing that I'm very happy with is the low noise floor.

The orange electrolytic is a 22uf Ceriatone cap I had laying around. The others are F&T.

The best thing with this build is trying the different voltages for the 1st channel. Playing with the dropping resistor to adjust the voltages just right was fun. I have the B+ down to about 211 to the 1st channel. This is what I measured on my FTR 37 as well.

-Rich
dehughes
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Re: Here is my GA40 build...check this bad boy out

Post by dehughes »

Agreed. Nice component choices. Love the build. Wish I could hear it in person.
Tempus edax rerum
loctal
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Re: Here is my GA40 build...check this bad boy out

Post by loctal »

That is a nice build! Glad to hear its quiet. I'm working out a GA75w build. Great seeing the old gibsons getting some love.
Cliff Schecht
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Re: Here is my GA40 build...check this bad boy out

Post by Cliff Schecht »

loctal wrote:That is a nice build! Glad to hear its quiet. I'm working out a GA75w build. Great seeing the old gibsons getting some love.
I have a hard time remembering which Gibson model does what, aside from the obvious R/RV/RVT tags. Why did you choose that particular model to build? Goofy tubes and a pretty simple design IIRC.
Cliff Schecht - Circuit P.I.
fzfwyv
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Re: Here is my GA40 build...check this bad boy out

Post by fzfwyv »

Inspiration came from two places:

1) My /13 FTR 37 click channel (heavily based on the GA40)

2) Victoria Electro King reviews & pics that I've read

And from what I hear coming out of my amp I think I made the right choice. The bonus is the trem channel which has a different character and the trem is pretty fun to play with.

The whole amp sounds different than the Marshall 18 watt and the Tweed Deluxe, both of which I've built and enjoy.

I would recommend this amp to anyone looking for something different and a reasonably simple 6V6 build.

-Rich
loctal
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Re: Here is my GA40 build...check this bad boy out

Post by loctal »

Rich,

I have been admiring your GA-40 all week. My question for you is how do you like the effectiveness of the tone control being as it is part of the phase inverter?

thanks, Ephraim
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