Restoring/repairing a Gibson GA-50

B. Adams · #1 06-06-2018, 08:51 AM

Long story short, the other day a friend of mine gave me a 1950-ish Gibson GA-50. I'm told that it was bought new and used as the PA system for bingo night in his parents local VFW hall until it closed in the mid 80's. His dad thought it was worth keeping so he saved it from being thrown away, and now it's sitting in my house.

It's all original except for new rubber feet. The leather handle has rotted away, but otherwise it's in excellent condition. However, being around 70 years old and probably never maintained, it doesn't work very well. The old paper condensers are probably the biggest problem, they're very obviously bad. It's noisy and hums like crazy, and I'm a little scared to even turn it on, but it works.

I'd like to get this thing going again, but I'm not sure where to start. I'm comfortable doing the work myself but I'm not sure where to source vintage or vintage-style components. I don't want to change the character of the amp by adding modern components. Due to that, I'm wondering if I'd be better off sending it to someone who regularly deals with vintage amps.

Two questions:
If I do this myself, where would be the best place to source components and parts?
If I send it to someone, who should I choose to do this work?

This isn't the best photo, but here it is:

muscmp · #2 06-06-2018, 10:45 AM

that is in great shape. i have a 1948 ga50t that has the tremolo.
do not even turn it on. especially if you know it hasn't been on for a period of time. the electrolytics will need replacing and possibly the some of the other caps and resistors. if you turn it on, there is the possibility that a cap will go and take out the power transformer.

that amp is a classic that was used by jim hall for years. it has two speakers in it. one 12 and one 8. usually jensens.

i've repaired mine as well as my other amps and i'll be glad to give you any assistance you may need.

around the july 4th holiday period you'll find companies such as amplified parts and tubedepot offering discounts on their products. register with them now and peruse their site. you can even find a strap as a replacement.

great find. PM me if need be.

play music!

B. Adams · #3 06-06-2018, 10:50 AM

Thanks for the advice! You'll definitely be hearing from me.

I haven't turned it on, and I don't intend to until it's been worked on. Everything I said about it's sound was based on what my friend told me about the last time he turned it on. I can't wait to hear what it sounds like once I get it back up and running again.

Now to start looking around for parts. This should be a fun project.

muscmp · #4 06-06-2018, 11:46 AM

here is the link to amplified parts. a lot of people use these F&T caps. you'll need three 10uf and one 20uf according to the schematic. the 22uf will be fine.
https://www.amplifiedparts.com/produ...CBrand%3DF%26T

you'll probably want to replace some of the signal caps also and may need to replace resistors. i don't worry about trying to find vintage caps that may or may not be in good shape. i'd rather have the most reliable components i can get and that would be the modern ones.

check that the speakers' cones are ok, too.

schematic

http://archive.gibson.com/Files/schematics/GA-50.pdf

note that the tubes are probably the metal type and as long as they are tested ok, i'd keep them.

play music!

The Growler · #5 06-06-2018, 10:30 PM

Sweet! That's a beauty.

clintj · #6 06-07-2018, 10:47 AM

I'd be looking at a full replacement of every electrolytic cap (+1 on F&T or Nichicon), measurement of other components to find broken or wildly out of spec parts (carbon comp resistors can drift quite a bit, or even crumble away when overheated), and that probably needs a death cap removed and a proper three prong power cord installed correctly.

I do some restoration and repair work on amps over in Idaho, but if you want a top notch tech I highly recommend Psionic Audio in Tennessee. Lyle there is very good and routinely deals with classics like yours.

And as said above, if one of those caps shorts out it can do quite a bit of expensive damage. Leave it unplugged until it's serviced, please. The thought that you can "reform" a vintage cap that old is bunk; the issue is that the electrolytic liquid evaporates slowly over time and no amount of conditioning will reverse that.