Jump to content
Gibson Brands Forums
Sign in to follow this  
robroy

help for my '61 GA-5T

Recommended Posts

Thanks for checking in! I recently acquired an awesome ga-5t that just began to act up: upon startup in begins crackling and then an ugly squeal..... that stops after a few seconds and then it's quiet again and remains that way until I turn it off.

 

I haven't had this amp very long, maybe a little over a month now. I just had a grounded cord installed and I wonder if something done then might be contributing to the problem. It wasn't having this issue right after I had that done but within a week or so.

 

I'm a total newbie with a few tools..... are there some obvious easy things to look for or should I just take it back to the repair shop? thanks much!

Share this post


Link to post
Share on other sites

You could try swapping the tubes out, one at a time, with new tubes and see if that fixes it. But it's quite likely that old components inside the amp are causing the problem. You'll want to bring it to a good shop and have them replace any electrolytic capacitors that are beyond their service life, which is like 10 years or so. Sometimes it's best to just strip out lots of the old stuff and replace it. If you could post a pic or two of the inside of the chassis maybe I could give you some tips on what to look for. Include the new 3 prong wiring so I can double check that work. [thumbup]

Share this post


Link to post
Share on other sites

It does appear to be a 1961 model. The power transformer has been replaced at some point. Here's a link to the schematic. If you don't have a copy print it out and keep it. You could even make a small copy and glue it to the inside of the cabinet somewhere if there's not already one there.

 

http://el34world.com/charts/Schematics/files/gibson/Gibson_GA-5T_61_Skylark.pdf

 

It looks like the electrolytic capacitors have been replaced. So the first thing to do is to replace the three tubes. You'll need (from left to right) a 12AX7 preamp tube, a 6BM8 power tube and a 5Y3 rectifier tube. I'd recommend a Tung Sol 12AX7, a Electroharmonix 6BM8 and a JJ 5Y3. Tube Depot is usually the best place to buy them if you don't have to pay Tennessee sales tax. Other good suppliers include Amplified Parts and The Tube Store.

 

https://www.tubedepot.com/products/tung-sol-12ax7-new-production-preamp-vacuum-tube

https://www.tubedepot.com/products/electro-harmonix-6bm8-eh-power-vacuum-tube

https://www.tubedepot.com/products/jj-5y3s-rectifier-vacuum-tube

 

You don't need to have them do any of the optional stuff like 'burning in the tubes' or 'matching the triodes.'

 

The other thing is that the 3 prong plug is wired wrong. That's not uncommon for somebody to do that. When the cord was replaced, they should have hooked up the new black and white wires differently that they used to be, so the juice coming in on the black wire hits fuse holder before the a/c power switch. Ignore the ground switch in the diagram. You don't have one - your's will be wired as if the ground switch is removed and the wires bypass the switch. The side of the fuse holder gets wired to the power switch and then from the power switch to the transformer and then on to the rest of the amp. See this diagram. Again, the new black wire from the power cord needs to be hooked up to the tip of the fuse holder. The side of the fuse holder is then wired to the power switch and the other side of the power switch still goes to the black transformer wire. The black transformer wire that used to be hooked up to the side of the fuse holder gets hooked up to the white wire from the new 3 prong plug wire.

 

Let me know how you make out. [thumbup]

Share this post


Link to post
Share on other sites

I got the wiring squared away today... the repair was graciously done for free! thanks again for the explanations and diagram. When I started it up afterwards the god-awful squeal was much shorter in length and not as intense... still there though. I have no idea why that would have changed but it did. I ordered the suggested tubes and they're on their way so I will start swapping them out soon. I have also been thinking about getting a replacement speaker to have on hand and would welcome suggestions for that.

 

here she is before I had the cord changed:

 

IMG_3474_zpsw0znpgmn.jpg

 

IMG_3475_zpsmijyxdsr.jpg

Share this post


Link to post
Share on other sites

ok, here's the latest: I put new tubes in and it ran quiet but the tone was not what it was before so I used deoxit on the old tubes and put them back in.... there is some crackling still on startup and even a little hesitation with the volume dial (?) but then it all quiets down and sounds great. Somehow I have lost my tremolo though! It was working fine when I got the amp less than two months ago but now there's no tremolo at all. I think it might have been damaged somehow when the grounded cord was hooked up incorrectly but I'm really not sure and I'm at a loss for how to fix it. Suggestions are welcome.

Share this post


Link to post
Share on other sites

Well, RobRoy sent his amp over for service and we did a recap and got the tremolo working. The speaker's not in very good shape but it sounds pretty good thru the 12" Weber Alnico here in the shop. We'll give it a little more TLC and see if we can't get everything up to snuff.

 

http://www.youtube.com/watch?v=UWp5VxP2eVE

Share this post


Link to post
Share on other sites

What a beautiful amp!

 

I have a Skylark from 1963 (Crestline, no tremolo) and I love it more than most things I own!

The tone is sensational. Just what I want - I don't even need any pedals!!

 

Very sound advice about getting the amp properly serviced. It's definitely worth it.

 

Hope you have many, many great hours playing through it.

 

Best,

 

Nick

 

---------------------

One Flight Up Music Studios Sydney

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...