About to aquire a Gemini I

[Doug Olitsky]

Hangman-

I'm going to be acquiring a Gemini I this week. Its been in a basement, long forgotten about for over 20 years. I'm going to rebuild it even before I power it up. I'll hit the power supply and all 'lytics.

While I'm in there I'll swap out all the film caps w/ Mallory 150's, any beatup looking resistors and all resistors in pwr supply and bias. Will pull the tone pack and put discreet components like I did for my Gemini II and VT22.

rewire the 7199 for 6U8A

I do have a question about the pwr spply. The Gemini I is quite similar to my Gemini II and I was thinking of beefing up the pwr sppply like I had done to my Gemini II.

Gemini II Pwr Spply filtering beefed up a bit as follows...
80 uf upped to 110uf (2x 220 in series w/ bleeder resistors)
40 uf's upped to 47uf
20uf's upped to 30uf

changed the 470ohm screen resistor to 1k ohm 5watt

On Richie Johnson's (of NY Repair & Guitar) suggestion I put in a 10k ohm 50watt resistor for the screen voltage... to bleed off the excess voltage and get it down to 430v again.

Is it a good idea to give my Gemini I the same treatment or just do as you had suggested in "that other ampeg site" and 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.

*** Gemini II mods for reference ***

[Hangman]

I think doing the filter caps is important. I don't think that beefing up the values is needed in the gemini 1. That being said, i have a g12 and I upped the value to 100uf I think.... though I may have done 64uf. (dual 32uf in parallel) I'll have to check when I get home. I upped other values from 40uf to 50uf and from 20uf to 32uf but that was more an issue of multi can capacitors. I only use F&T, don't trust the JJ caps,and don't trust the CE caps, so F&T makes them in Dual 50 and dual 32. those were the options i had. If F&T made exact replacements in that form, I would've used them.

I definitely don't think 50W resistor is necessary for the screen supply. thats a lot of unnecessary heat/power dissipation for what amounts to a pretty minor change in voltage. The 7591s can take it, why bother?

the 470 ohm resistor for the screen supply on the g12 is fine. honestly its probably fine on the gemini II.

I tend to think of the Gemini I as one of ampegs finest designs, Ive done some experiments with mine and I always end up putting it back to stock. (aside from the minor changes in the filter caps)

Hangman-

I'm going to be acquiring a Gemini I this week. Its been in a basement, long forgotten about for over 20 years. I'm going to rebuild it even before I power it up. I'll hit the power supply and all 'lytics.

While I'm in there I'll swap out all the film caps w/ Mallory 150's, any beatup looking resistors and all resistors in pwr supply and bias. Will pull the tone pack and put discreet components like I did for my Gemini II and VT22.

rewire the 7199 for 6U8A

I do have a question about the pwr spply. The Gemini I is quite similar to my Gemini II and I was thinking of beefing up the pwr sppply like I had done to my Gemini II.

Gemini II Pwr Spply filtering beefed up a bit as follows...
80 uf upped to 110uf (2x 220 in series w/ bleeder resistors)
40 uf's upped to 47uf
20uf's upped to 30uf

changed the 470ohm screen resistor to 1k ohm 5watt

On Richie Johnson's (of NY Repair & Guitar) suggestion I put in a 10k ohm 50watt resistor for the screen voltage... to bleed off the excess voltage and get it down to 430v again.

Is it a good idea to give my Gemini I the same treatment or just do as you had suggested in "that other ampeg site" and 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.

*** Gemini II mods for reference ***

[Doug Olitsky]

Thanks for posting the advice. Always best to ask. I'll keep it simple and follow your lead, since you have gone through w/ experimentation and have gone back to original design.

Let me know if you did 100 or 64uf.

I'll post some mug shots one amp is acquired.

Doug

[Hangman]

Thanks for posting the advice. Always best to ask. I'll keep it simple and follow your lead, since you have gone through w/ experimentation and have gone back to original design.

Let me know if you did 100 or 64uf.

I'll post some mug shots one amp is acquired.

Doug

Im out of town right now, won't be back until the 15th.
if you have a blue check gemini, there isn't as much room for putting the dual F&T cans, I recall saying to use the 80uf Axial F&T, but I always forget that those are 450V rather than 500V.

I'd say replace the multi-can they originally had in there with the dual 50 or dual 32. then use the axials as you have been for the rest of it.

[Doug Olitsky]

No rush, once back after the 15th you can give me the details. Hope your trip is a fun one.


Got amp home last night. Overall its nice. No dolly and one metal foot and metal corner missing. Will have to find replacements. Maybe tubes and more has the correct hardware.

Was the the dolly optional???

I opened it up and all looks good. No signs of stress on any of the components and all the tubes are original and test good (bugle boy and sylvania).

Other than the 'lytics and death cap are there any parts I should change as preventative maintenance? Resistors, caps, etc.

I was going to swap out the green and yellow CDE caps, but should I leave well enough alone if they are part of the mojo.

What about the caps in the tremolo circuit, some have mentioned changing them as they work hard.

understood on the multi sect caps. matter of fact on my G-15 I drilled out the original multi section can to stuff w new caps.











Looks like this missed quality control, look @ tags they were never soldered!!


This amp is 7868 based, built in 1966.

[Hangman]

very clean! yeah the dollys were optional.

the CDE caps aren't part of the mojo. But they don't detract from the mojo either.
They are good caps, I tend to leave them unless they are failing, simply because thats the sort of bloke i am.

Some folks just feel better replacing old parts because they never know when they might start leaking or failing... etc... thats fine too. These old ampegs are really great amps and they used good parts most of the time. but its not like a vintage fender where if you pull the old blue caps the amp loses some value.

interesting about the unsoldered tags too. Thats for the footswitch and reverb right?

[Doug Olitsky]

Good advise. I will just leave alone for now, do the important stuff and have a listen!

Yes the unsoldered tags are for the foot switch. Amazing that slipped by




I'm gonna do

F&T 50/50uf @500v (replace the multi can)
F&T 30uf @500v (2 of them zip tied into old 20/20 bracket)
F&T 100/100uf @500 (use one section, make a bracket to mount on original multi-can bolts, inside chassis)

that will keep em all at 500v if the 100uf can is too big for my bracket idea I'll do a Sprague Atom 80uf @ 450v

and of course the 3x 25uf @25v.

will post results

Doug

[Doug Olitsky]

Mission Accomplished!

All the parts arrived while I was away on vacation, spent the weekend doing the job.

Did the power supply w/ 100 - 50 - 50 - 30 - 30 all 500v F&T
Upgraded all the 25 uf caps
Changed the caps in the tremolo
Rebuilt Baxandall w discreet components
Rewired the 7199 for 6U8A
Cleaned chassis and cabinet
Deox pots and sockets
Built a dolly, thanks to Bruce @ FlipTops for the Dolly Knob assembly

http://www.fliptops.net/catalog/p-100531...cartsdolly

W/o a polarity switch I did leave the power cord as is. Depending how amp is plugged in it will run a bit quieter. So I put in a new film death cap. I'm not terribly concerned... A lot of the time I use a ground lifting plug on gear to minimize ground loops, so that negates a grounded plug anyway. Have a cord ready to go if I want to add in the future.

Brought it back to life on a variac and all was calm and uneventful. After watching the amperage draw for a while, played some chords and all was good. Good tone, and volume, reverb and tremolo work and original AlNiCo Jensen sound fine.

All the original tubes are tested strong and are being used, except the 7199. I got a pair of novar/magnoval socket adapters. When the outputs do wear out I can then use EH 7868's w/o worrying about the sockets. I use the adapters in my Fisher 400 and my Gemini II.

http://www.ebay.com/itm/201359204289

Jim McShane is a good tube source and he will even sort out a pair of 7868's that run "cold".

[Hangman]

When I got home from Vacation I forgot to post the capacitor values for my G-12

I did 100 - 50 -50 -32 -32, similar to what you ended up using. although all of mine were F&T Multi-caps.