Gibson GA40T Les Paul Schematics

[gingertube]

HELP.

The local Guitar God is in the habit of asking me to build him amp clones.

So far I've done a Trainwreck and a (sort of) Tiny Terror for him. He recently played a vintage amp he loved and tells me it is a Gibson GA40T Les Paul, he wants one but does'nt want to pay the several thousand bucks they were asking for it. I've agreed to look into building him one.

I can find schematics for a GA40 Les Paul, and for a GA40T which are quite different beasts but can't find a GA40T Les Paul. Can anyone point me in the right direction?

Off for the next few days will check back Monday next week.

Thanks,
Ian

[BLT]

There doesn't appear to be a GA40T Les Paul. It seems to be one or the other; a GA40T Mariner or a GA40 Les Paul.

[Stevem]

Off the top of my head I would agree, the Les Paul models or that era never came with tremolo!

[Dingleberry]

There is two different schematics for GA-40 Les Paul amp. Earlier models 54' - 56' had 6sj7 preamp tubes and 6sn7 p.i. and from 56' (iirc) they used 5879 preamp tubes and 12ax7 p.i. Pair of 6V6's cathode biased in the power section. Both of them has tremolo. Never have heard one of the earlier ones, but the 56' GA-40 is probably my favorite amp ever. Chewy fat singing tone and really sweet tremolo. GA-40T is a totally different animal.

[Richie]

The Gibson amps can get confusing. You may have to ask your friend more details in what the amp looked like.. But basicly most of them were the same except in construction from hard wired, then to eyelet boards, or different looking cosmetics of the outside, or the LP logo to the 2 tone, tweedy looking ones. lots of info in this video.

https://www.youtube.com/watch?v=YIeJ4NaTapQ

You might also ask your friend, which channel he liked best. The amp has 2 channels that use the 5879.

Another route is ask your friend if he has tried a GA20T. Its very similar to the GA40, except it uses a 12AY7 for one of the channels. Which you can tweak some and use a 12AX7. And pick which channel your friend liked in the GA40,and use that one for the 5879. Lots of really great sounding Gibson amps out there. Also use a good speaker for that amp.
I have a friend that has a few of the different GA40s, and the GA20T. Your friend might need to check out a GA20T too..

[Lindz]

Any idea which schem applies to the 58? I found a few online. like that one best and would not mind taking a crack at that circuit

[Craig B]

There is a youtube of what looks like a GA-80 but the owner calls it a GA-40. Is that the same amp?
Craig B

[Gainzilla]

This could be it. Followed the youtube link, watched it (pretty cool, btw), dug around a bit... Kinda makes me want to give one of these a crack.

Interesting tidbit, the cabs were made of redwood throughout the entire time these amps were in production (like '54-'61). The circuit changed, and the cab style changed, but it was always with Redwood. Lighter, and possibly more resonant. Anyway, I digress...

[Richie]

Here is some info. I would say[but just guessing] it would be the GA40..
So, you'd have to ask your friend to be sure that is the correct model.

Buffalo amps use to build a clone of the Gibson amp,and also Victoria.

According to the 1958 Gibson catalog it would be the 2-tone amp,and it would have the eyelet board. Lots of pics and info on these amps on the net.

Also if you have ever worked on these, the signal caps are on the underside of the board,and a pain to get to to if you need to replace them.

http://www.gbase.com/gear/gibson-les-paul-ga-40-1957

http://www.gbase.com/gear/gibson-ga-40-1958-brown-tan

http://www.vintageguitarandbass.com/gib ... 958_30.php

http://www.classictubeamps.com/schemati ... ematic.pdf

http://s159.photobucket.com/user/mad_do ... k.jpg.html

http://www.victoriaamp.com/amplifiers-2/

[gingertube]

Thank You all,
Further investigation has showed that this is the one he wanted.
http://bmamps.com/Schematics/gibson/ga40.pdf

Now to order in some 5879, I have everything else required (I will first try some Brimar 6BR7 I have in stock).

Cheers,
Ian

[Richie]

Might get a few of the 5879, and go through some to find a good one.

[gingertube]

There is two different schematics for GA-40 Les Paul amp. Earlier models 54' - 56' had 6sj7 preamp tubes and 6sn7 p.i. and from 56' (iirc) they used 5879 preamp tubes and 12ax7 p.i. Pair of 6V6's cathode biased in the power section. Both of them has tremolo. Never have heard one of the earlier ones, but the 56' GA-40 is probably my favorite amp ever. Chewy fat singing tone and really sweet tremolo. GA-40T is a totally different animal.

So we want the '56 circuit -
Take a look at the schematic to see what is "different" about the GA40 Les Paul:
An "old fashioned" basic paraphase phase splitter (for that fat tone?), not even the later self balancing version.
AND
An interesting tremolo done by modulating the B+ and screen voltages to the pentode input tube.
That tremolo scheme probably means that sticking with the 5879 pentode will be easiest.

Cheers,
Ian