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gibson ga15rvt and ga20rvt amps
gibson ga15rvt and ga20rvt amps
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Old 11th October 2014, 11:25 PM   #1
muscmp is offline muscmp  United States
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Default gibson ga15rvt and ga20rvt amps

both amps need some work.

1. ga15rvt has an electrolytic that is green at the solder joint. do i just resolder or replace the cap? see image below.

2. ga20rvt needs quite a bit. it has incorrect power transformer, T1. incorrect choke, L1. needs output transformer, T2. also needs recapping.

the ga20rvt probably wouldn't get more than $300-400, so is it worth it to buy new parts(i don't trust ebay used parts) from heybour, mercury or hammond IF they are available?

recommendations?
thanks,

Click the image to open in full size.

ga20rvt schematic.

Click the image to open in full size.
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Old 11th October 2014, 11:51 PM   #2
shanx is offline shanx  Canada
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These amps are a labour of love to restore, so I think it depends on if you want a working servicable amp, or a museum piece. If museum piece then on the GA-15 you may not want to touch anything. \The GA-20 has been modded so need to evaluate if its working, maybe just bring up to scratch on electrolytics, etc. You have not detailed if they are actually working on not, so you would need to get more details, pictures of the amp etc..
Edcor is reputable and reasonable cost for transformers and chokes.
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Old 11th October 2014, 11:57 PM   #3
muscmp is offline muscmp  United States
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Quote:
Originally Posted by shanx View Post
These amps are a labour of love to restore, so I think it depends on if you want a working servicable amp, or a museum piece. If museum piece then on the GA-15 you may not want to touch anything. \The GA-20 has been modded so need to evaluate if its working, maybe just bring up to scratch on electrolytics, etc. You have not detailed if they are actually working on not, so you would need to get more details, pictures of the amp etc..
Edcor is reputable and reasonable cost for transformers and chokes.
i'd like to have working serviceable amps. the ga15 works fine so would probably only need that cap and a couple others replaced, if necessary.

the ga20 needs, minimum, the output transformer before i can even plug it in.
thanks,
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Old 12th October 2014, 11:32 AM   #4
shanx is offline shanx  Canada
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Is the output transfo missing or blown? BTW I would recommend converting the ac mains cord to a 3 wire properly polarized and grounded plug.
If you have the OT then may be possible to get it rewound...
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Old 12th October 2014, 03:53 PM   #5
muscmp is offline muscmp  United States
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Quote:
Originally Posted by shanx View Post
Is the output transfo missing or blown? BTW I would recommend converting the ac mains cord to a 3 wire properly polarized and grounded plug.
If you have the OT then may be possible to get it rewound...
the OT is missing, and, yes i will change to a 3 prong cord.
thanks,
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Old 13th October 2014, 07:33 PM   #6
muscmp is offline muscmp  United States
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Default input impedance for output transformer

i checked with edcor and they need to know the input impedance for the output transformer. i know that the output is 8 ohm but i don't know the input. how do i find that out?
thanks,
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Old 14th October 2014, 04:34 PM   #7
costis_n is offline costis_n  Greece
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If one electrolytic is dead, better change them all, they are of the same vintage....
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Old 14th October 2014, 06:13 PM   #8
muscmp is offline muscmp  United States
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i found that i need 8-10000 ohm input on the output transformer. unfortunately, the edcor appears to be larger than the original and with 4 screw holes so i may have to just attach only two of the four or look to hammond or heybour for the OT. mercury is just too expensive for this project.

costis: yes, i'll definitely replace the electrolytics.
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Old 25th October 2014, 12:47 AM   #9
shanx is offline shanx  Canada
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Don't know if you have chosen which supplier, but you should be fine with Hammond or Heyboer. Surprised that Edcor did not have a tranny frame that would be compatible though. Better I think not to have to start drilling out the amp chassis.
PS Do you think the market price 300-400 range for that amp in working condition may be a little low? I have no idea what the outside looks like, and I'm not in a position to do anything other than ask.
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Old 25th October 2014, 01:10 AM   #10
muscmp is offline muscmp  United States
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Quote:
Originally Posted by shanx View Post
Don't know if you have chosen which supplier, but you should be fine with Hammond or Heyboer. Surprised that Edcor did not have a tranny frame that would be compatible though. Better I think not to have to start drilling out the amp chassis.
PS Do you think the market price 300-400 range for that amp in working condition may be a little low? I have no idea what the outside looks like, and I'm not in a position to do anything other than ask.
i got the hammond 1750e at a decent price thru amplified parts. since there was no output transformer in the amp, i'm having to rely on the schematic. there are 3 wires, blue, brown and red. i can figure out the output to the speaker but the input/primary has me confused. obviously i need to get it correct.

the outside is in great shape except for a couple of small holes in the grill cloth.
thanks,
mikeB.
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