Gibson GA-5 Skylark tone mod

[Resonator Guy]

I recently purchased a Gibson Skylark amp on ebay that was cosmetically just about mint. When I received it, the power cord was badly chewed and very brittle so I replaced it with a new three pronger. Fired it up and of course it worked very poorly. Loud, loud hum that howled as you turned it up. I got my new electrolytics from AES yesterday, did the cap job and tried it again. At first I figured I had done something wrong because there was no hum, no white noise, nothing. But I plugged a Melody Maker in anyway and it worked beautifully, except I found it somewhat bright sounding. Not harsh, just real bright. I know I can adjust the tone control on my guitar, however, with a lot of them that kills the tone.
Are there any easy changes that can be made to this beauty that will make her sound more mellow? I don't want to add tone controls or anything like that, just cut the brightness a bit.

[dkevin]

Ear Piercing GA-5

I have several of these amps and they can be made to calm down on the treble end with a little care.
First, with the schematic in hand, make a layout drawing and compare the actual components with the alleged components. It is not uncommon for Gibson/Kalamazoo to make all sorts of undocumented changes to the schematic.
Next, look for the #$%$@ 102C84 Sprague network. It is a combination of resistors and caps sealed in epoxy. Usually it is located at the volume pot. If you have one, kill it on sight.
I have found that a mix of Mallory 150's and Orange Drop 716P's works best in these amps. That is, make the first interstage cap an Orange Drop and the remaining one(s) Mallory 150's.
If you are still too thin, look for an undocumented .1uf cap on V1B cathode bypass. If it is there, get rid of it and the amp will open up.
Lastly, consider a speaker change if you have done all of the other work first. I have found the Gibson Ultrasonic speakers (10 inch Alnico) to be tolerable if the rest of the amp is squared away. But if you do decide to go with a different speaker, try a Fender blue alnico. MMMMmmmmm!

[Jazz P Bass]

Gibson sparkle

Hate to say it , but that is the way the amp was designed.
It is what it is.
That being said, I would up the value of that 250uuf capacitor (250picofard).

[Resonator Guy]

GA-5 sounding better all the time

Thanks guys. I don't seem to have one of those resin coated items mentioned. I will experiment with a few different caps.
What value(s) would you suggest trying to replace the 250uuf cap?
BTW, my wife says that if it is supposed to sound that way, then I must have done it right, so leave it alone, but we can't do that, can we.
I did try it with a couple of darker sounding guitars (teles with humbuckers) and it does sound pretty darn good.

[J M Fahey]

Don't butcher it please.
Sell it to somebody who appreciates it and buy something else.
Just my two cents.

[Resonator Guy]

I don't believe changing a cap would ever be considered butchering anything. Did my posts sound like I wanted to ruin it? I don't think so.

[dkevin]

Re; Butchering amps

I know this is probably a tender subject... but...
In my opinion, an amp that is almost universally panned for being "too thin and shrill- especially at higher volumes" is not a sacred cow. I am not convinced that leaving it as is (unmolested) enhances its value when it looks nice on the outside but is not tolerable to play or hear.
This is precisely why I gravitated to Gibson amps in the first place. They (especially the Crestline series) are not highly prized for their tone as designed. They are point to point wired and easily modified. They provide an excellent platform for experimentation and as previously mentioned, can be greatly improved.
If anyone desires a closet queen to serve as an investment for the future, there are other amps that will always be in high demand if never (and I mean never) have any components replaced. Gibson amps, and in particular, this Gibson amp is not one of them.
Oh. and by the way, this may be the "Way it was designed" but it can and does sound better.

[J M Fahey]

Hi resonator guy
You're right, you did not, that's clear, but I saw some of the hair rising suggestions, which were *not* just "changing one little cap" .
By the way, I would also have suggested raising that 250pF to 500pF, but not more.
Why? , because the small magnet, small coil, thin paper speaker is the big limiting factor there, coupled to an undersized transformer.
The bass cut is intentional.
Besides, remember Gibson designed for big fat dark guitars (their own), not exactly for bright jangly Fenders.
Sending more bass than what can be supported does not mean more bass, but farting or muddying.
Why didn't I say so? Because it had already been suggested.
But:

look for the #$%$@ 102C84 Sprague network. It is a combination of resistors and caps sealed in epoxy. Usually it is located at the volume pot. If you have one, kill it on sight.
I have found that a mix of Mallory 150's and Orange Drop 716P's works best in these amps. That is, make the first interstage cap an Orange Drop and the remaining one(s) Mallory 150's. <-- Why?
If you are still too thin, look for an undocumented .1uf cap on V1B cathode bypass. If it is there, get rid of it and the amp will open up. <-- "open?"
Lastly, consider a speaker change if you have done all of the other work first. I have found the Gibson Ultrasonic speakers (10 inch Alnico) to be tolerable if the rest of the amp is squared away. But if you do decide to go with a different speaker, try a Fender blue alnico.

qualifies as butchering, at least in my book.
I'm sure if you need all that, you'll be happier with another amp, or, even better, building one from scratch.
And please, don't be that sensitive, no insult was meant and if you found it so, I apologize in full.
<--I prefer to use these.

[Jazz P Bass]

Vintage Gibson Skylark

I would have thought the "do not butcher" came from the heart.
You have a pristine , classic amp there.
You should feel proud of it.
You may well find the amp cannot put out bass tones well.
They consume more of the available power & require a "better" speaker.
That is what I said about the amp being engineered that way.
Do the future members of this forum a service (and all vintage amp lovers) and document any changes. Make a copy of the schematic & any changes made. Keep it with the amp.


30 years from now a post to this forum.
Hi. I have a Gibson GA Skylark & it does not sound crisp enough.

Enjoy the amp

[roughcut studios]

How do we figure out where to draw the line between, how much is it worth, and do we want to USE it for what it was made to do? Are we wealthy enough to invest in history, or are we scraping up the dough for an amp to play and simply want it to sound sweet and be reliable enough to really use? Are we robbing future generations by changing worn out caps and off value resistors?
How do we decide what to do with our vintage gear? This is a very hard question for me, as I tend to want to be able to enjoy using my collection of stuff,(valuable or not) rather than just look at it and wish I could use it. My present dilemma is what to do with a very early McIntosh hifi amp (20w2), which I have been told by someone that to change any part and make it safe to use would reduce it's value by 80%!!!. Nice paperweight! What to do???
Will this question ever be able to be answered?

[Jazz P Bass]

Modified Amps

Mod the Mac & enjoy it
Document the changes.
I repeat: Document the changes.
Keep the parts.
I have a 1962 Bassman that I had to replace a few caps on.
They are in a bag, safely tucked away in the back of the amp, with a copy of the schematic, with notations of what was done.
(Why in the world I have to keep bad parts is beyond me!)
I saved the 2 prong power cord & the death cap.
I had to redo the tolex because some fool back in 1972 wanted a black amp.
Should I keep the scraps of black painted tolex?

[Resonator Guy]

Allright, we will right finished to this one.
Thanks for the clarification, JMF, and JazzPBass, your suggestions are generally right on.
New JAN power tubes and a Mullard rectifier are in it now and I think I am done. My Les Paul Special sounds great through it as well as several others. I may up the value of the cap at some point but right now it is working great and looking even better.

I still have three amps near my work bench that others have "fixed" in the past. I am continuing to fight my way through them and I do document all my changes.