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Topic: Info needed on old Gibson Amp............ |
Jerry Hayes
From:
Virginia Beach, Va.
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Posted 4 Apr 2008 12:02 pm |
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I just got home from a flea market with a little treasure for $100. It's an old Gibson all tube amp with one 12" speaker. On the top plate it says "Gibsonette Tremolo, model GA-8T, serial #101701. It works great and the tremolo sounds killer. The front grill cloth is missing and there's been one of those round metal speaker cover grates added. Here's some info I'd like to have if anyone knows........
What approximate age is the amp......
What color was the original grill cloth and is it available anywhere.
What the wattage is.
Was there originally a logo on the front of the amp and if so, are they available anywhere.
Approximate value of the amp....
Any help would be greatly appreciated. Here's a few shots of it!
 ......JH in Va.
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Don't matter who's in Austin (or anywhere else) Ralph Mooney is still the king!!! |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 4 Apr 2008 1:40 pm
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Approximately 1960, 1961, or possibly as late as 62. They had a 10" speaker early, then moved to 12". You should also be able to look at transformer or pot date codes. Should be 6BM8 tubes, which are basically a 12AX7A triode preamp and 6BQ5-type power tube in the same bottle. The grille cloth should have been a brown-red type, similar to tweed Fender amp - at least the two I have owned did. The nameplate is one of those plastic Gibson logos - the earlier version had a bit thinner logo with no backing, the later one had backing. I see the logos at vintage guitar shows from time to time, and I think they're using something similar in some of the more recent Gibson amps, so it may be possible to get a repro. The original speaker should be one of the cheapie Jensens, either P12S, P12T, something like that. Here's a pic, later version logo:
http://www.informatik.uni-bremen.de/~dace/gg/GA-8T_front.jpg
There's a schematic of the 2-6BM8 version here:
http://www.drtube.com/guitamp.htm#Gibson
They say 9 watts - probably about right. It sort of looks like perhaps the entire baffle was replaced. That same site has a bunch of pictures, here's one from the back that shows the plywood baffle:
http://www.informatik.uni-bremen.de/~dace/gg/GA-8T_rear_02.jpg
This is a truly great amp. IMO, the finest sounding tremelo I ever have owned. I sold my '60 10" speaker version to one of the guys I still work with - he still uses it - I bought it ages and ages ago. I replaced it with a GA-20T Tweed Ranger - also great.
Value is very subjective. Last version of the VG price guide I have lists these for $400-575, but that's in excellent original condition, which this is nowhere close to. But still - you did great for $100. |
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Jim Peters
From:
St. Louis, Missouri, USA, R.I.P.
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Posted 4 Apr 2008 2:39 pm
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Jerry you are very lucky. That is a great little amp! Mine got misplaced by my son, it is gone forever. JP
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Carter,PV,Fender |
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Jerry Hayes
From:
Virginia Beach, Va.
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Posted 4 Apr 2008 2:42 pm
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Dave, thanks for all that good information, I really appreciate it a lot........JH in Va.
_________________
Don't matter who's in Austin (or anywhere else) Ralph Mooney is still the king!!! |
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Rocky Hill
From:
Prairie Village,Kansas, USA
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Posted 5 Apr 2008 7:08 am
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The Gibson amp behind me in my picture I got in 1968. I use it everyday! It's a Gibson Scout GA-17RVT. Great amps, you got a great find.
Rocky |
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Jerry Hayes
From:
Virginia Beach, Va.
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Posted 6 Apr 2008 1:58 am
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I've heard that these can be wired up so there's a three prong power cord. Is that really possible and is it hard to do? I think I'd like to have a ground in the amp to avoid unexpected zaps from time to time. The power cord which is now on the amp looks like one of those brown extension cords you can buy in the grocery store..........JH in Va.
_________________
Don't matter who's in Austin (or anywhere else) Ralph Mooney is still the king!!! |
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Rocky Hill
From:
Prairie Village,Kansas, USA
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Posted 6 Apr 2008 5:24 am
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I've got to that on mine also! I take my meter and check the chassis to ground every time I move it. I make sure the chassis isn't hot, lets say my amp has lit me up more than once.
Rocky |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 6 Apr 2008 7:13 am
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Any amp can be properly wired with a grounded, 3-prong power cord. I think this should be done on any amp except a pure collector item that's not used seriously - and done by a qualified tech so it's done correctly. The worst thing you can have is an amp you think is properly grounded and isn't.
Till you get that done, get a 3-to-2 power cord adapter which has polarized blades, which mates with a polarized receptacle. Using an AC voltmeter (range around 120 VAC or a bit higher), check the voltage of the chassis with respect to a true ground and orient the adapter so that the voltage is near or at zero. The other orientation is reversed-ground, and the chassis sports the full 120 VAC line voltage. Not a good idea. But this should be a temporary solution, IMO. Further, anyone that doesn't understand what I'm talking about here simply shouldn't plug the amp in at all until the amp is properly grounded.
The other thing people sometimes do is figure out which is the correct orientation and mark the plug corresponding to the polarized blade. But this is even more problematic, since sometimes old wiring doesn't have polarized receptacles and that old plug will just fit in fine either way. Having the polarized adaptor plug at least alerts you to the fact that there's an issue.
Be careful with this - a reversed ground, on either your own amp or someone else's amp or the PA, can get you electrocuted. I don't, personally, know anybody that's been killed by this, but they're out there, and I have seen people get shocked very badly. |
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Jerry Hayes
From:
Virginia Beach, Va.
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Posted 7 Apr 2008 11:15 am
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I remember when I first started playing out and all the amps were only two prong. If we'd get a buzz from the amp we'd just turn the plug over and it seemed to work but that was a long time ago....JH in Va.
_________________
Don't matter who's in Austin (or anywhere else) Ralph Mooney is still the king!!! |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 7 Apr 2008 5:51 pm
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Yeah, I've used a bunch of amps that way myself. If the only potential danger was a reversed ground, that would be one thing. But there are other potential problems that cause your chassis to carry lethal voltages.
For just one example, suppose a capacitor or some other amp circuit element that was supposed to present a high resistance between the B+ (main DC supply voltage - in a tube amp anywhere from 350-500 or even 700 volts DC) and the chassis suddenly shorted out for some reason. Yup - you guessed it - you now have that voltage on the chassis. If your guitar has a string ground - a wire that connects your strings to the ground leg of the guitar circuit, which connects directly to the chassis of the amp through the guitar cord - then you are directly exposed to that voltage. Unless there is some path with a much lower resistance to ground than through your body, then a significant current may well flow through you if you are not highly insulated from ground. A good amp ground is that alternate low resistance pathway to ground, and can save your butt.
I always yell at bandmates if they play barefoot. That often guarantees that their body presents a low resistance to ground. I ask them if they ever heard about the admonition to never play with electrical applicances while in the bathtub. If there's a serious electrical fault onstage, it can be about the same thing. And I've seen some doozies of electrical faults.
BTW - if it bothers anybody out there that I sometimes play with people who sometimes play barefoot - remember that I can't control them anymore than they can control me.  |
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