Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => PC Express and JSchem - Schematics and Layout diagrams => Topic started by: tubenit on December 24, 2012, 11:43:30 am

Title: Gibson GA-77
Post by: tubenit on December 24, 2012, 11:43:30 am

Thanks to DummyLoad and Willabe for this contribution!

With respect, Tubenit

Title: Re: Gibson GA-77
Post by: mk_716 on October 04, 2021, 05:40:58 pm

Hey Tubenit,
   How are you?

   Thinking about building this with the reverb/tremolo (GA-77RVT) - thinking about using this as a starting point - do you have (or know of) a layout for the RVT version?   This is what I'm thinking about...  I'll probably replace the 7199 (unobtainium) for the 6U8A and use 12a*7 for the EU7s.

   I've read the Willabe build post too, I'll probably re-work the tone stack based on his observations... (Hi Willabe, read lots of your threads!)

   Schematic:

     https://el34world.com/charts/Schematics/files/Gibson/Gibson_ga77rvt_crestline.pdf


   Thanks in advance for your help.

m.

Tubenit p.s.  I'm in the finishing stages of the 6k6 with a switchable FX loop and PPMIV - It's not done, but nearly so - I'll post a build thread up in the Low Watt thread.   It's fantastic!  Chimy, articulate - exactly what I was after for a pedal platform - thanks so much for the design and layout - I used Doug's stock board into the bargain.

Title: Re: Gibson GA-77
Post by: Willabe on October 05, 2021, 05:15:40 pm

That GA-77RVT is a very different amp than a GA-77. It won't sound anything like the GA-77 I built. It's not a GA-77 with reverb and tremelo added, if that's what your looking for? I'm not saying it's not a good amp, I don't know.  :dontknow:   

See if you can go on line and find out some more about how that amp sounds before you commit to building it. I think some of the Crestline series amps are not as highly favored by Gibby amp fans? You have to watch out though because some guys think ANY vintage amp they buy is great, because it's vintage!   :icon_biggrin:  They buy an old amp, crank it, it distorts and "man this thing sounds sweet!"  :l2:  Compared to what?

I think part of it is just wanting something old, to be part of the crowd, bragging rights.  :dontknow:  Which is fine, "Hey look at what I got. Wow that's cool!" There's a whole lot of old vintage amps, and guitars, that aren't great sounding, that the price has gone through the roof because of this. It's vintage, it's gotta sound great!  :undecided:

There's a lot going on in that RVT, it will take some time to lay the whole thing out properly. It's not a beginners build. I don't know how many amps you've built from scratch including the layout? Not trying to talk you out of it, just want you to think it through.

Title: Re: Gibson GA-77
Post by: mk_716 on October 05, 2021, 08:14:14 pm

Hey Willabe,
   Thanks for the reply and the advice.   I'm still up in the air about it myself.  I did read a few good things about it. 

   I'm going to build a 6L6/EL34 something in a 2 x 10 combo cab I have.    I have a good friend that was an amp tech for decades really dug the Crestline models, then I read your thread and it got me thinking. 

   All the stuff I've been building have been something old, lol!  And yeah, that's part of it.  I'm trying to look outside the Fender/Marshall world a bit - but it's tough to get info on some of these more obscure amplifier lines/models.

   I've done a few scratch builds (from schematics), adapted a few existing designs and did a few by the book from proven designs/layouts.   Most of my builds take me forever to finish anyway, I tend to research stuff to death before I build anything, often going down rabbit holes and never getting built (this may be one of those).

   I'm looking at 2 channel designs, I've got the speaker/cab, iron, 6L6s and 6550s.   I am no longer gigging, I build the amps for my own entertainment/intellectual interest. 

   I'm open to suggestions, thanks again for looking out.

mike

   

Title: Re: Gibson GA-77
Post by: Willabe on October 06, 2021, 10:07:35 am

Mike, you should read these if you haven't yet;

Lead dress;

http://www.geofex.com/Article_Folders/lead_dress/lead_dress_in_tube_amps.htm

Grounding;

http://www.valvewizard.co.uk/Grounding.pdf

Title: Re: Gibson GA-77
Post by: mk_716 on October 06, 2021, 10:19:27 am

been there, done that!

I actually like the debugging/fine tuning part!   I used a valvewizard/tubeswell ground lift in my Revibe build.  I probably learned more about grounding/lead dress on that Revibe build than any of the amps I've built.  Finally finished the carpentry on the cabinet for it, painted it the requisite black this week - as soon as it's done gassing off I've got some silver tolex going on it.

Lead dress is part art/part science - every build I've gotten better. 

Thanks W!