• From: Greeley, CO
  • Registered: 2007-02-10
  • Posts: 10

Topic: Gibson GA-5T Skylark hum problem

I recently bought a Gibson GA-5T amp off ebay.  The guy who sold it to me said it had a hum, but he never said it was as bad as it is.  When I received it, I turned the volume and tremolo knobs to 0, plugged it in and turned the power on.  After about 10 or 20 seconds, a loud hum comes from the speaker.  Being a novice (this is my first tube amp), I didn't really know where to even begin looking for the problem, and read somewhere that it may be just a bad tube.  I purchased a new set of tubes, installed them and the amp did the same thing.  I finally resorted to letting it sit for a few days to drain any remaining electricity stored inside, and proceeded to open the back armed with a can of compressed air and a can of contact cleaner.  I tackled all of the dirty stuff and proceeded to power the amp back up and still, to my dismay, it hummed.  Like I said, I'm a novice and I know it would be best to take it to a repair person, but I don't know anyone who does amp repair in my city.  This amp is from the 1960's and looks entirely original, so I don't think anyone else has messed with the insides.  It even has the original speaker and two-prong cord (I know I should install a 3-prong for safety purposes, and any info on that would be appreciated).  The tubes are as follows:  (1)6X4, (2)6AQ5A, (2)6EU7.  Any info you guys could give me would be greatly appreciated!


- J -

  • From: Almancil, Algarve, Portugal
  • Registered: 2006-09-02
  • Posts: 6,205

Re: Gibson GA-5T Skylark hum problem

Toney,

Just a thought here. If it only has a two wire chord there is no earth to unit, perhaps it should have an earth to the chassis. I have know other electrical appliances hum when the earth contact is broken.

Roger

"Do, or do not; there is no try"

Roger Guppy's Website

  • NELA
  • Honoured Member
  • Offline
  • From: West Monroe, La. 71292
  • Registered: 2007-11-28
  • Posts: 1,303

Re: Gibson GA-5T Skylark hum problem

That is very possible, Roger but if it is "double insulated" (like in most of today's power tools) it does not require a "ground". With what little knowledge I have on electrial equipment I just don't think a "double insulated" tool was manufactured in the '60's. Toney, maybe you need to check to see if the electrical cord has been replaced prior to your purchase.

Nela

NELA's Website

  • badeye
  • The Blues Fixer
  • Offline
  • From: Cape Breton Island, Canada
  • Registered: 2006-09-02
  • Posts: 3,381

Re: Gibson GA-5T Skylark hum problem

You may have the wrong Southpaw.  Southpaww51 said he was a newbie. Southpaw41L would be Toney. no.

CSI...Badeye.

one caper after another
  • From: Almancil, Algarve, Portugal
  • Registered: 2006-09-02
  • Posts: 6,205

Re: Gibson GA-5T Skylark hum problem

Ooops sorry southpaww51,

I must learn to read properly lol

Roger

"Do, or do not; there is no try"

Roger Guppy's Website

  • From: Greeley, CO
  • Registered: 2007-02-10
  • Posts: 10

Re: Gibson GA-5T Skylark hum problem

just an update everyone, I found out that the amp just needs a few capacitors replaced.  does anyone happen to know where I can find some caps (and it looks like a couple of resistors) for this particular amp?

  • From: Madeira Beach, Florida
  • Registered: 2007-12-05
  • Posts: 3,312

Re: Gibson GA-5T Skylark hum problem

southpaw51,

You can probably just bring the bad components to your local radio shack and they will likely have (or can order) replacements. Be sure to label or draw a diagram (or take a photo) of the wiring before you remove them to ensure you install the replacements in the right place!

Rule No. 1 - If it sounds good - it is good!
  • From: Greeley, CO
  • Registered: 2007-02-10
  • Posts: 10

Re: Gibson GA-5T Skylark hum problem

topdown,
 
    Great idea, I hadn't yet considered that.  I will get out my soldering iron and let you know how it goes.

  • From: Greeley, CO
  • Registered: 2007-02-10
  • Posts: 10

Re: Gibson GA-5T Skylark hum problem

Hey everyone, thought I'd let you know that I picked up a few caps from torres engineering, threw them in the amp, and it's working perfectly now.  I did, however, wonder why the amp doesn't seem to break up very well.  It definitely gets loud, but it only breaks up a little even when I have the amp cranked to 10.  Does this have anything to do with the fact that the filter caps I put in were of a higher voltage than the originals?  I've read reviews that this amp is supposed to start breaking up around 5 or 6, but mine just sounds clean...... I can use a pedal, no problem, but I was just wondering if this is indicative of a more  serious problem