Ben Eckroth Posted November 12, 2012 Share Posted November 12, 2012 Hello all. Like the title says, a friend of mine has given me her late father's Gibson GA-55V (along with his L-forty-something that was unfortunately stored in an attic for the last 20 years) because she's moving and would rather someone have it that plays....instead of them just sitting in a corner unused. Needless to say, I'm rather excited. From doing research, I've found that they made this amp between 1954 and 1958, shipping only around 480. It has a nifty little vibrato unit that plugs directly into your guitar's output and has a switch along with two controls, "frequency" and "intensity" The only source codes I've found so far are on the speakers, which are both Jensens--one made in '55 and the other in '54. There is also a code stamped on the transformer, but I cant make it all out, and spent the last couple hours playing her....so she's rather hot...I'll hopefully get in there later after everything cools down. Sorry, I just had to vent my excitement to someone because my girlfriend thinks I'm a nut-ball. Getting to the things I'm curious about: 1) Does anyone have experience with this amp....because finding information on this guy is pretty hard. My TUBE AMP BOOK doesn't even have the schematic for it. 2) It clearly says ninety-something watts but every resource says it is only 18. I'm just curious about this....I really don't care what the wattage is. 3) Anyone know where I can find a user/service manual for it Any help would be greatly appreciated. Thanks Ben Link to comment Share on other sites More sharing options...
Grog Posted November 15, 2012 Share Posted November 15, 2012 Hi, I have the Gibson Master Service Manual, it only has a GA-55 & a GA-55RVT. Is the vibrato unit separate from the amp? Link to comment Share on other sites More sharing options...
Ben Eckroth Posted November 15, 2012 Author Share Posted November 15, 2012 Here are a few pics: The little box I'm holding is the vibrato unit (missing a knob). It's wired into the first instrument input and from the research I've done, Gibson decided not to include the V model or the schematic for the vibrato unit on the amp schematic because so few were made. If anyone could verify that information...it would be awesome. I found this one Guitar Center's Vintage page....the description says GA-55TV...but if you look below the standby knob it clearly says Ga-55 V. Looking at the upper right picture, the little black box mounted below the back panel is the vibrato unit. It plugs in to a 1/4" jack mounted inside the back panel but the jack just has its lugs wired together so it doesn't go anywhere. The wire coming out of the unit is what's wired into the first input. I don't know if this is done so you can plug into the first input and still use the vibrato....I'm really not sure. Guitar Center Gibson GA-55v Anymore information you may have would be appreciated. Thanks Link to comment Share on other sites More sharing options...
Grog Posted November 16, 2012 Share Posted November 16, 2012 Here is whats in the Gibson Service Manual for the GA-55 PS............ It looks like I'm maxed out on my upload quota, PM me your email address & I'll email it to you. Link to comment Share on other sites More sharing options...
DavidRamey Posted November 18, 2012 Share Posted November 18, 2012 here is some info for you Gibson Garage Link to comment Share on other sites More sharing options...
Ben Eckroth Posted January 16, 2013 Author Share Posted January 16, 2013 Thanks for all the input! I've pretty much found all of that information already. Here's my next concern: I'm thinking of taking the original speakers out, and using reissues because I'm afraid to damage the original ones from the fifties. Think that's a good idea? Or am I just being over paranoid? I originally though the amp had Jensen field coils in it because there's a transformer mounted on one of them, but it's actually the OT. Had I taken the time to read....I would've noticed the speakers have "PM SPEAKER" written directly on the magnet cover. Again, thanks in advance Link to comment Share on other sites More sharing options...
Ben Eckroth Posted January 29, 2013 Author Share Posted January 29, 2013 Also, I'm finding conflicting information with the number of tubes. One resource says it has 9 tubes (which it does), but only states the two power tubes, the rectifier tube, the inverter, and two preamp tubes-which by my count is only 6. There are three more "metal" tubes that are (what I'm going to call) spring-loaded. I have to push them towards their sockets and slightly twist them to remove them. I believe they are 6j5 tubes, I'm just trying to figure out what exactly these little guys do because even the schematic for the ga-55 from Gibson omits them. Link to comment Share on other sites More sharing options...
Willabe Posted February 24, 2015 Share Posted February 24, 2015 I know this is an old thread but the GA-55V schematic is in the 3rd and 4th edition of the Jack Darr book; Electric Guitar Amplifier Hand book. I don't know if it's also in edition's 1 and 2. But there looks to be at least 2 parts connections in the schematic that are drawn wrong. The B+ supply string between the phase inverter(PI), 6SC7, and the mixer, 6SN7 is missing a connection 'dot'. And an added wire connecting 1 of the PI plates to the wiper of the vibrato channel volume. Willabe Link to comment Share on other sites More sharing options...
Beckroth Posted May 28, 2016 Share Posted May 28, 2016 Thanks Willabe! This is incredibly helpful as the schematic I originally referenced was missing the entire vibrato section. Although, someone else told me it was identical to the vibrato used on some other models (of which I can't remember at this point). The amp has been playing well for the past few years but has developed a serious hum as well as the audio gradually fading in and out, as well as some scratchy pots. I'm hoping the audio issue is just a bad tube somewhere. The power tubes have been replaced but I haven't messed with any of the other ones. My current project is to tear it down, repair what needs repairing, and give all the components a designation on the schematic so It's much easier to troubleshoot in the future. If it's to anyone's interest, I will post pictures of the board with overlaid designations, as well as an updated schematic when I'm finished. It will take me a while though.... Thanks again! Link to comment Share on other sites More sharing options...
badbluesplayer Posted May 31, 2016 Share Posted May 31, 2016 Thanks Willabe! This is incredibly helpful as the schematic I originally referenced was missing the entire vibrato section. Although, someone else told me it was identical to the vibrato used on some other models (of which I can't remember at this point). The amp has been playing well for the past few years but has developed a serious hum as well as the audio gradually fading in and out, as well as some scratchy pots. I'm hoping the audio issue is just a bad tube somewhere. The power tubes have been replaced but I haven't messed with any of the other ones. My current project is to tear it down, repair what needs repairing, and give all the components a designation on the schematic so It's much easier to troubleshoot in the future. If it's to anyone's interest, I will post pictures of the board with overlaid designations, as well as an updated schematic when I'm finished. It will take me a while though.... Thanks again! I'll be interested to see what you find out. Link to comment Share on other sites More sharing options...
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