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#1 2012-05-07 17:05:10

beedoola
Member
Registered: 2009-05-24
Posts: 58

Just got a Gemini I; needs some love

I got a Gemini I, at I think a fair price with a Weber Bull Dog speaker.

It has the 2 prong cord and I'd like to put a 3 prong in there, how would I do it/any diagrams for it?

Also the large can cap ( I'm guessing) is stock, what is a replaceable value to use?

Also..the choke...how can I gauge it's reliability? Looks beat..

The Trem also doesn't not work, not sure what the deal is.

Also; what caps should be changed? Any particular parts to go-to in replacing? The .1 uf caps look pretty old and there are a few ceramic that look bad - the material wore off or melted off onto other components.

http://i157.photobucket.com/albums/t54/Beedoola/301b76e1.jpg
http://i157.photobucket.com/albums/t54/Beedoola/2f4226f9.jpg
http://i157.photobucket.com/albums/t54/Beedoola/14f5a6b9.jpg
http://i157.photobucket.com/albums/t54/Beedoola/e8729921.jpg
http://i157.photobucket.com/albums/t54/Beedoola/b530e221.jpg

Last edited by beedoola (2012-05-07 19:45:59)

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#2 2012-05-07 20:07:40

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Just got a Gemini I; needs some love

Wow,  someone did a real number on that one.   

That ain't a choke,  that's your output transformer.... Looks like it might've failed at some point and some body cut it open and re wired it or something... Can't tell from the photos... Is it burned anywhere? 

The can should be a 70x40x40.  450v. 

When I do those I find a place to mount an axial 80 uf 450v on the tag board,  and then use a 50x50  for the remaining 40 uf sections.

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#3 2012-05-07 20:08:49

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Just got a Gemini I; needs some love

I'd leave the coupling caps alone unless they are failing

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#4 2012-05-07 21:41:20

beedoola
Member
Registered: 2009-05-24
Posts: 58

Re: Just got a Gemini I; needs some love

There is some electrical tape around the output transformer. The amp works but I'm not sure if its 100%

Will do on the can. What about the addition of a 3 prong cord, any links on line to a diagram?

And the trem, I'm not really sure where to start with that. I have the footswitch but someone cut the connector so I installed a TRS jack on the back of the chassis and a TRS plug on the foots with; the reverb works, switch works for it but I get noting with the trem with the switch or with the controls.

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#5 2012-05-08 08:25:44

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Just got a Gemini I; needs some love

Have you tried swapping the tremolo tube?   Its possible the bulb in your optoisolator is dead.   If you have a scope toucan check and see if the oscillator is working....

Three prong.... 
http://theguitarfiles.com/guitarfile644.html

That explains it for a fender....  But it's pretty much the same thing for your ampeg.

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#6 2012-05-09 18:59:47

beedoola
Member
Registered: 2009-05-24
Posts: 58

Re: Just got a Gemini I; needs some love

yeah I tried a different 12ax7; when I engage the trem with the footswitch, there is a faint clicking sound- the LFO I'm assuming, the speed changes when I adjust the speed control. This mean I have a bad bulb in the term unit? If so; can I replace just the bulb or do I need to find a whole LDR/LFO whatever thing. If I can replace it; what is the bulb spec?

Also, can the output transformer impedance be measured when the amp is off? - like a speaker can be measured without power. If the OT can be measured when the amp is off; I think mine is messed up cause I'm not even getting 1ohm on my DMM. The speaker is supposed to be 8ohm I think -its measuring 6.7 or more.

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#7 2012-05-09 22:23:57

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Just got a Gemini I; needs some love

The transformer should measure less than an ohm on the secondary.   That is normal.   You need to put a test tone through the transformer to really test what's going on.

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#8 2012-06-03 17:17:59

beedoola
Member
Registered: 2009-05-24
Posts: 58

Re: Just got a Gemini I; needs some love

hangman wrote:

I'd leave the coupling caps alone unless they are failing

I was wondering if any of them were problematic like in the V4s - I think it was the .01 glass caps or whatever they are, in the V4 that you mentioned often go bad, so I swapped those out in my V4. I wanted to know if there were any components that were a go-to, to replace when servicing these.

I'm gonna order the 50/50 can and the 80uf axial soon.

I get a loud pop when I turn the amp off, do I need to wire a cap in somewhere on the power switch to stop that? I added a three prong cord...

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#9 2012-06-30 19:07:00

beedoola
Member
Registered: 2009-05-24
Posts: 58

Re: Just got a Gemini I; needs some love

Is there a way to test the Vibrato module to determine whether its messed up or not? I tried swapping in a new tube but that didn't help - all I get when the term is engaged is a very light, barely in audible click of the LFO - does away when I bypass the Vib.

Is this vim module the cheapest alternative as a replacement for the stock?

http://www.fliptops.net/catalog/p-10008 … s-tm1-m1-r

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#10 2012-07-02 17:43:22

hangman
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From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: Just got a Gemini I; needs some love

Do you have a scope?

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#11 2012-07-03 19:59:07

beedoola
Member
Registered: 2009-05-24
Posts: 58

Re: Just got a Gemini I; needs some love

I do not but my buddy might. If I'm able to use one, what should I be looking for/how do I conduct the test?

**Edit. Sorry, I forgot you suggested using a scope already. If the bulb is bad, is it possible to open up the Opto and replacing the bulb?

Last edited by beedoola (2012-07-03 20:15:23)

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#12 2012-07-16 14:51:03

beedoola
Member
Registered: 2009-05-24
Posts: 58

Re: Just got a Gemini I; needs some love

I recapped my Gemini today, just wanted to make sure this was right, I used the schematic linked below... Hangman - I used the method you mentioned with the dual 50/50 and the 80uf Axial.

http://www.drtube.com/schematics/ampeg/g12-jp.gif

http://i157.photobucket.com/albums/t54/Beedoola/a941d722.jpg
http://i157.photobucket.com/albums/t54/Beedoola/a26ac63b.jpg


ALSO,

When I got this Gem, the Volume pot and guitar IN for Channel 2 had both been connected. I reconnected the Volume pot but I had a question about the Resistors for each input. The schematic I linked above appeared to be dead on for the Filter Cap but not for the inputs, the schematic below seems to be like my Gemini.

http://imageshack.us/f/199/ampeggemini1schematic.png/

Are the "Accordion" inputs the ones that the 100k to ground?

Last edited by beedoola (2012-07-16 14:52:17)

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