59Panhead Posted December 19, 2014 Share Posted December 19, 2014 Hello, from Roxboro, N.Carolina. I found this forum while searching for some Thor amplifier parts. Which led me to see what others may have posted about them, and then what others may have posted about the GA-40's. I have two complete Thor amps and one totally trashed one, three early GA-40 Les Paul amps, and two of the next model GA-40 Les Paul amps. I am not a practicing musician. I only play guitar well enough for my own enjoyment, and to know when I have an amp in proper working condition. The amps that I just listed are not the only ones that I have. Just a few of the Gibson models. I was making mods to the trashed Thor, when I noticed that the Power/Polarity switch was broken beyond repair. I bagged it up for parts, and started my search for another switch. I don't generally mod old amps. Just restore them to their proper working condition, and stop there. I have not touched the other two Thors, as there are too many projects ahead of them. Neither work, but are complete. This one is a chassis (complete), faceplate panel (broken switch), and two speakers (one with a 3" tear). The mods include a Bias level pot and component changes to center the pot when the correct Bias is set on a set of JJ 6CA7 tubes. I have old stock tubes, but no NOS. Figured I would set if for modern tubes. Along with this mod, I added an external test Jack to measure plate voltage. Another mod was to add a Passive Effects loop. I installed a Hum Balance pot, as I have had success with these in other amps, original and project builds. There's still a low level hum, but I read where another fellow said that he installed a .022uf cap on each leg of the Primary lines, hot and neutral, that cleaned this right up. I may have read that here, but I don't remember. I will give those a try, when I replace the Power switch. Found a suitable replacement (I hope). Lastly (for now), I installed a thermistor on the line feed to the Primary. I like a nice slow startup on a cold amp. On this little amp, the current draw is so low that the thermistor never really gets hot like they would on one that draws closer to 2 amps. So, the resistance value drops my line voltage to something close to original specs. I measure my line voltage to be 123-124vAC, and after the thermistor, 117-118vAC. The ones that I use are rated for 3A. Anyway, I'm starting to browse the forum, and will comment and hopefully contribute to some of the topics. Looking forward to my stay. Have a good one. Jack Link to comment Share on other sites More sharing options...
the dog Posted December 19, 2014 Share Posted December 19, 2014 Hello, from Roxboro, N.Carolina. I found this forum while searching for some Thor amplifier parts. Which led me to see what others may have posted about them, and then what others may have posted about the GA-40's. I have two complete Thor amps and one totally trashed one, three early GA-40 Les Paul amps, and two of the next model GA-40 Les Paul amps. I am not a practicing musician. I only play guitar well enough for my own enjoyment, and to know when I have an amp in proper working condition. The amps that I just listed are not the only ones that I have. Just a few of the Gibson models. I was making mods to the trashed Thor, when I noticed that the Power/Polarity switch was broken beyond repair. I bagged it up for parts, and started my search for another switch. I don't generally mod old amps. Just restore them to their proper working condition, and stop there. I have not touched the other two Thors, as there are too many projects ahead of them. Neither work, but are complete. This one is a chassis (complete), faceplate panel (broken switch), and two speakers (one with a 3" tear). The mods include a Bias level pot and component changes to center the pot when the correct Bias is set on a set of JJ 6CA7 tubes. I have old stock tubes, but no NOS. Figured I would set if for modern tubes. Along with this mod, I added an external test Jack to measure plate voltage. Another mod was to add a Passive Effects loop. I installed a Hum Balance pot, as I have had success with these in other amps, original and project builds. There's still a low level hum, but I read where another fellow said that he installed a .022uf cap on each leg of the Primary lines, hot and neutral, that cleaned this right up. I may have read that here, but I don't remember. I will give those a try, when I replace the Power switch. Found a suitable replacement (I hope). Lastly (for now), I installed a thermistor on the line feed to the Primary. I like a nice slow startup on a cold amp. On this little amp, the current draw is so low that the thermistor never really gets hot like they would on one that draws closer to 2 amps. So, the resistance value drops my line voltage to something close to original specs. I measure my line voltage to be 123-124vAC, and after the thermistor, 117-118vAC. The ones that I use are rated for 3A. Anyway, I'm starting to browse the forum, and will comment and hopefully contribute to some of the topics. Looking forward to my stay. Have a good one. Jack Welcome to the forum....I have a 74 shovelhead.....I know a little off topic but I like panheads.... Link to comment Share on other sites More sharing options...
59Panhead Posted December 19, 2014 Author Share Posted December 19, 2014 Welcome to the forum....I have a 74 shovelhead.....I know a little off topic but I like panheads.... And, a bit off topic back at you. I have a '76 Shovelhead FLH, that I bought new in January of that year. I would take cross-country trips on it, as a younger man. It's been in every state, but Rhode Island, Hawaii, and Alaska. Totaled it on 01Sep04, when I center-punched the side of a minivan. I have the parts to put it all back together. Just too many other projects ahead of it, I guess. The '59 has always served me well. It's stock. I always call it my rolling restoration. Jack Link to comment Share on other sites More sharing options...
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