Jeddy-3 Posted April 3, 2013 Share Posted April 3, 2013 Hello Everyone, A good friend recently gave me his '65 GA-75 amplifier. Does anyone here have the same amplifier? I know it's very rare. The amp sounds pretty good but could be better. It hums a great deal. I know from someone on TDPRI that the power tubes are mismatched and he stated that that alone could be the source of the hum. I talked to someone else who said that the filter capacitors might need to be changed. Lastly, the markings of the 4-selector switch on the amp's control panel have been rubbed off over the years. I'd love to know what it is supposed to do. 1.Can anyone here have the manual for this amp, or a copy of it? I already have the schematic. 2.Does anyone have any specific tube recommendations that they prefer in the amp? 3.Can anyone who has the amp possibly send a photograph of the top of the control plate and the inner chassis electronics? Mine appears to have had the electronics "messed with" and the job was pretty messy. I'd love to see that the inner chassis should look like so that I can restore it to factory spec. Any help would be greatly appreciated. The amp was free so I don't mind spending a little money getting the old girl back in business. I hear that the clean tones are quite nice, which is good because I've been getting into jazz guitar. Thanks so much for any info anyone can provide. Quote Link to comment Share on other sites More sharing options...
Grog Posted April 3, 2013 Share Posted April 3, 2013 Hi Jeddy, I don't have this amp, but I have a collection of amps from this era. I tried to buy one of these a number of years ago on ebay & came in second best. It looks like most of your caps have been changed, except for two. They might be the culprits, or like you said, it might be a tube. This amp is quite rare, only 181 were shipped like yours. 74 were shipped with a 15" JBL. Enjoy your amp! GA-75.pdf Quote Link to comment Share on other sites More sharing options...
PartsPvt Posted June 7, 2013 Share Posted June 7, 2013 I have (since 1967) a '67 GA75 Recording..2X10s. Mine is the only 1967 made 1 of 1.. Not totally original..but close. New caps and tone mod Selector is OFF STANDY ON ON (reverse ground) Mine is converted to three prong now though. A friend did the mods years ago. Quieted it further at idle..as we used it in studio. An amazing sounding beast.. Also note the speaker jack..and another extension speaker jack With the tone stack mod it KILLED my Twin Reverb..both clean and nasty ..both LOUD though. I use it on Neck pickup on my 355 Stereo..mod'd Traynor YBA1A for bridge.. With the Les Paul Custom it screams..with my '65 ES175 the big box just is buttery.. You did good.. Very Rare and quite amazing sounding..for RnR or Jazz..great in studio. Your 1965 is 1 of 17 made. GA-75 Recording (Crestline) 25W 2x10" or 1x15"? Guitar Combo Speakers: 2x10" Inputs: 2+2 Channels: 2 Volume Controls: 2 Tone Controls on Each Channel: Bass, treble Tremolo: No Reverb: No Tubes: 6 (Pre (2x6EU7, 1x6CG7 (aka 6FQ7)), Pow (1x6L6 PAIR + 6C4)) Diodes: 3 Extension Speaker Jack: No Monitor Jack: Yes Watts Output: 25 Shipping Totals: 1963: 58, 1964: 91, 1965: 17, 1966: 15, 1967: 1 Schematic with 2x 6EU7, 1x 6C4, 1x 6FQ7 & 2x 6L6GC (1963 or later) http://www.0rigami.com/gg/amps2.html#GA-75_75W Quote Link to comment Share on other sites More sharing options...
GA Ampman Posted August 8, 2013 Share Posted August 8, 2013 I have a 1964 GA 75L it is a amazing amp the switch is off, Stand buy, On and On with polarity switched. they had a two prong plug was original so you needed it to kill the hum and stop from getting shocks. If you still need pictures let me know and I will send some. For Tubes US made NOS are worth the money and in a Gibson amp they will last for 20 years. Quote Link to comment Share on other sites More sharing options...
jmj5150 Posted August 19, 2014 Share Posted August 19, 2014 I am currently rebuilding a 1963 Gibson GA-75 and need some advice on the caps I replaced below. I followed the schematic as best as I can but still confused if I connected the 20uf capacitor to the diode correctly. I am going to put a VVR3 in place of where the monitor jack is to get distortion at lower levels. Quote Link to comment Share on other sites More sharing options...
PartsPvt Posted September 19, 2014 Share Posted September 19, 2014 Just saw your PM..sent you more pictures. Hope it helps.. Mine breaks up nicely...but at some high levels.. A beast ans a beauty of an amp... Quote Link to comment Share on other sites More sharing options...
jmj5150 Posted September 28, 2014 Share Posted September 28, 2014 Just saw your PM..sent you more pictures. Hope it helps.. Mine breaks up nicely...but at some high levels.. A beast ans a beauty of an amp... Thank you for sending me the pics How did you get the JBL speakers to fit in the cab because I have 2 Fender JBL D110F that won't fit due to output transformer size. Did you replace the output transformer with a smaller one? Quote Link to comment Share on other sites More sharing options...
Fouzyamp Posted January 31, 2020 Share Posted January 31, 2020 Hello Je suis en France et je viens de finir de restaurer mon Gibson ga75 de 1965, j'ai changer les condensateur électrolytiques ainsi que le cablage qui était très abîmé...et maintenant il sonne a merveilles, et est très silencieux (aucun bourdonnement) les tubes de puissance sont des sylvania et les preamp des RCA et milliard. Sur votre photo il me semble que les condensateur 10uf a coté du pont de diode sont câblé a l'envers( le + dois être a la masse) En tout cas merci d'avoir poster ces photo qui mon aussi aidées a la restauration de mon ga 75 Cordialement Benj Quote Link to comment Share on other sites More sharing options...
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