Unknown Ampeg Gemini modificationss

[Queen*Son]

Well I took the amp out anticipating a new tm1 for the tremolo and I wanted to look at some of the mods that were done.. of the 3 1/4" jacks 1 is for the pedal and the two in the middle are for a 4ohm and 8ohm out. There is a switch in between them that runs to something I haven't seen on another gemini. Maybe we can figure it out? I'm green, but learning. Also I found that the trem intensity pot is 3m, but seems original.

Edit... I can't upload any more pictures..

[Jon Snell]

I have absolutely no clue without at least detailed photographs and preferably a schematic of the work done.
No pictures are uploaded.

[Queen*Son]

Let's see if this works.
https://ibb.co/G7ZDHz8
https://ibb.co/9WQvG0T
https://ibb.co/tsm2ztr
https://ibb.co/zbXQd3W

[Jon Snell]

I would say it has been bodged and you have your work cut out to return it to standard.
Looks like bias has been mucked around with as has the reverb.
Good iuck!

[Queen*Son]

Hmm, I'm not necessarily trying to get it back to stock it sounds as good or better than my original Gemini... Weird, reverb works great. I'm curious about that first picture, if you see there is something along that wall, with a white box on it, thats what the switch runs to, not sure what for though.

[Queen*Son]

And not sure about the other legs to that speed pot, also bizzare that it works... I think?.. Now I'm second guessing myself. What would a cathode bias mod be for? it doesn't appear to me missing anything from that circuit, just a few things added? haha. Thanks for pointing out those oddities as well, I never would have noticed them, this is helping me learn a lot about my amp. Thank you.

[Queen*Son]

Also from what I see there is ever only 1 wire connected to that leg of the pot.

[Delta362]

On the pot with the white wire going to the wiper, is the right leg soldered to the pot's metal housing to pick up a ground? If so, that could be why we don't any other wires on it.

[Queen*Son]

Delta, I did a quick Google search and haven't seen any Gemini with more than one wire soldered to that pot, and I'm not an engineer so I'm sure what you're thinking is correct! How about that first picture with the weird round pot and the white upside down box, thats what the switch runs to... hmm. Also Jon pointed out that bizzare cathode bias thing? not sure what thats about maybe someone was trying to make it fixed bias?

[Queen*Son]

It looks like that white wire goes to that weird little bread board piece?

[The Dude]

Hard to tell for sure, but that "white box" looks to be a coupling cap routing AC voltage to the bias supply circuit. What AC voltage do you have on either/both sides of the cap? Also, it looks like one side of it isn't soldered very well.

Edit: Someone probably changed it from cathode bias to match this schematic.

https://drtube.com/schematics/ampeg/g15-jp.gif

[Queen*Son]

Hey Dude! just held a flashlight under the amp by the switch and I see an old engraving that says auto cathode on one side.. can't make out the other side..any guesses? I'm just now really learning about tube amps and bias etc.

[The Dude]

My bet is that it's switchable from cathode bias to adjustable/grid bias. Who knows how they labeled it.

[Queen*Son]

You got it! kind of cool or super lame? I'm not mad at it honestly and I bet my guitar player friends will like it for more headroom. Plus it will be nice to play the rhodes through and not HAVE to be dirty, it stays really clean, and loud, especially with the 2 10s. I wish they were labeled so I knew if they should be 4 ohm or 8ohm lol. Thanks dude! I can't wait to install the new tm1 module.

I've got 2 things noticed.. The treble switch doesn't engage the treble boost, and the tremolo speed pot is pretty fast even at low, and then full speed at full, but not much in between. hoping the tm1 solves that.

[The Dude]

......especially with the 2 10s. I wish they were labeled so I knew if they should be 4 ohm or 8ohm lol......

Measure them with a DVM. DCR will be slightly less than actual impedance.