'52-'54 GA-40 Schematic

[Jack Hester]

This is my first post here, and I haven't had a chance to do much browsing. In the past couple of years, I've begun re-learning my earlier training in tube amps. I am better than 30 years removed from that time, and am enjoying the return. I did do some searching here (and quite a few other places) for a better schematic of the earliest GA-40 Les Paul amps, and keep coming up with the same bad quality one. For the most part, I have the schematic drawn out using ExpressSCH, where I broke it down to three separate drawings. Power Supply, Pre-Amp, and Tremolo/PI/Power Amp. The component values, for the most part, have been entered. But, there are still a few that I had to guess at. So, I'm curious if anyone had found a better resolution schematic of this vintage amp. When I am sure that I have my drawing finished and accurate, I plan to post for all who have had the same problem as I. Thanks for any help.

Jack

[oc disorder]

Hi Jack and welcome to the forum..
I don't know the model... not too many here downunder but
in a previous posting on this forum http://music-electronics-forum.com/t11316/ Fyl provided this link for a GA 40 :-
http://www.harpamps.com/gibson/pg_0181.jpg
This forums search engine (top right) can be invaluable sometimes !!!

It seems to be from the Gibson Amplifier master service book
which used to be on Schematic Heaven nearly 180 megs of it !
I'm sure if you 'oogle it someone will have it available for download should you need it for reference.

Schematic Heaven have some GA40's too but maybe they are the hard ones to read
eg
GA-30rvt Invader
GA-35rvt Lancer
GA-40 1954
GA-40t Crestline
GA-40 Les Paul
GA-45rvt Les Paul Preamp
GA-45rvt Poweramp
GA-46
GA-50-60-70-80

http://www.webphix.com/schematic%20h...om/gibsonamps/

Hope thats at least some help and hope it goes well for you.

Keep us posted!

[Jack Hester]

Hi Jack and welcome to the forum..
I don't know the model... not too many here downunder but
in a previous posting on this forum http://music-electronics-forum.com/t11316/ Fyl provided this link for a GA 40 :-
http://www.harpamps.com/gibson/pg_0181.jpg
This forums search engine (top right) can be invaluable sometimes !!!

The one I need is not the typical like you have posted in the above link. I'm thinking that '54 was a crossover year, with the one I'm looking for ending, and the one above becoming the design for later models. The schematic, that I'm trying to find a better resolution for, has a 3-position switch for frequency, and no depth control. The later ones, like the above link shows, has a frequency pot and a depth pot. But thanks for the response. I'm thinking that I will have to make a correct drawing from the real thing. But at least, there will finally be a hi-res drawing with component listings, when I'm finished.

Jack

[Jack Hester]

Made a new schematic that I can read.........

I made this schematic by marking up a poor copy printed from one of the many that I downloaded. I compared values from two different originals amps, one having untouched original components. So, I was able to get legible values for the ones on the drawing. I am posting my finished drawing so that others will have something better to read. A couple things to note. I found that C16 and C17 are both 20uf, in the same can. I left the drawing as it was, for these. But, both the amps that I checked were the same for these values. Just a Gibson thing, I guess. Also, I didn't draw the PT on my layout. It's a fairly straight forward connection.

One thing that I will do, the next time that I have my hands inside one of them is to take voltage readings and make a chart. Don't know when that will be. Maybe sometime this year, I hope. Anyway, hope this makes life easier for someone else troubleshooting theirs. Have a good one.

Jack