My mid 60's Ampeg guitar amps: Gemini II and VI AND Reverbrocket II

[gravityhigh]

I have 3 mid 60's Ampeg guitar amps. A Gemini II, a Gemini VI, and a Reverborocket II. The only one I've been able to use is the Gemini VI and I love it! I'd like to get the other two working better.

The RRII has a pretty bad hum. I had it serviced (cap job, etc) and the hum only got worse. Could it be my tech installed bad caps? he had to put them in different places because he didn't use a multi cap like it originally did. Does having the filter caps outside the chassis somehow reduce hum??? Is it possible that one of the transformers is causing it?

I bought the Gemini VI from the original owner and gave it a cap job and new tubes. It sounds great! but gets kinda hot, I'm not sure if there's much I can do about that. In its original 1x15 combo cabinet I would never want to take it out of the house because its so huge and heavy... so I sought a head cabinet, which is what lead me to purchase the Gemini II that conveniently was being sold in a head cabinet! So now I have the VI head and a 1x15 external cab for gigs! The G II didn't have any tubes when I got it and I've never tried to fire it up... I'm assuming it's the same amp just with II channels, does anyone have one and like it? One of these days I'm going to fix it up.

Are there any experts on these amps out there who could help me trouble shoot or give me some tips on cleaning up the hum?

Thanks!

[Jazz P Bass]

Hum can be caused by many different things.
Narrow it down.
Do any controls affect the amount of hum?
If so, the issue is before that control.
Are the power supply nodes relatively ripple free (Vac)?
Does pulling the phase inverter tube stop the hum?
Does the amp hum without a guitar plugged into the input?

[gravityhigh]

no guitar and all tubes - hum sounds like harmonic series, buzzy 120 240 480 etc
no 12ax7 preamp tube - just a little bit of low hum when volume is up all the way
no phase inverter - no sound

[Jazz P Bass]

Are the power supply nodes relatively ripple free (Vac)?

[twangman1]

I have 3 mid 60's Ampeg guitar amps. A Gemini II, a Gemini VI, and a Reverborocket II. The only one I've been able to use is the Gemini VI and I love it! I'd like to get the other two working better.

The RRII has a pretty bad hum. I had it serviced (cap job, etc) and the hum only got worse. Could it be my tech installed bad caps? he had to put them in different places because he didn't use a multi cap like it originally did. Does having the filter caps outside the chassis somehow reduce hum??? Is it possible that one of the transformers is causing it?

I bought the Gemini VI from the original owner and gave it a cap job and new tubes. It sounds great! but gets kinda hot, I'm not sure if there's much I can do about that. In its original 1x15 combo cabinet I would never want to take it out of the house because its so huge and heavy... so I sought a head cabinet, which is what lead me to purchase the Gemini II that conveniently was being sold in a head cabinet! So now I have the VI head and a 1x15 external cab for gigs! The G II didn't have any tubes when I got it and I've never tried to fire it up... I'm assuming it's the same amp just with II channels, does anyone have one and like it? One of these days I'm going to fix it up.

Are there any experts on these amps out there who could help me trouble shoot or give me some tips on cleaning up the hum?

Thanks!

I have a Gemini VI and a Gemini II. The Gemini VI I have had since 1973 and it has been my main amp all these years, a real workhorse. Love it love it love it. The Gemini VI has 6L6's while the Gem II has 7591's. Seems rare to find a Gemini VI with 6L6's--they are definitely original equipment, not a retrofit; they're on the schematic as such. The VI has only broken down a couple of times in all these years. I plug a 57 Esquire into a first generation RAT pedal, a volume pedal, and an EP2 Echoplex through the Gemini VI. GREAT tone! Get lots of comments about that. Plenty of volume (got the tinnitus to prove it). Run it at about 50-60% and rely on the RAT for serious overdrive. The Gemini II I have had since the late 70's and it has been less reliable. A whole series of different maladies--right now trem is out on it. The darker sound of the ampeg matches well with the brightness of the tele/esquire. I had a couple of Les Pauls, but the only one of those that sounded good through the VI was a Deluxe with the mini-humbuckers.

[52 Bill]

I recently had an Ampeg come in with a similar hum problem. Previous tech had replaced the can cap with a new one, but mounted it down with a metal mounting ring. The original one was mounted with a phenolic ring. The metal ring caused a ground loop and a persistent hum. Remounted the can cap and all was good.

What I'm trying to say here is that these amps are prone to grounding hum problems if the original ground schemes are not followed. Try having the new caps grounded more like the original one were and see if that helps.

[Bruce / Mission Amps]

I recently had an Ampeg come in with a similar hum problem. Previous tech had replaced the can cap with a new one, but mounted it down with a metal mounting ring. The original one was mounted with a phenolic ring. The metal ring caused a ground loop and a persistent hum. Remounted the can cap and all was good.

What I'm trying to say here is that these amps are prone to grounding hum problems if the original ground schemes are not followed. Try having the new caps grounded more like the original one were and see if that helps.

I've had to fix a few of these old Ampeg amps where someone freshened them up with new filter caps but did not follow EXACTLY the original Ampeg grounding scheme.

[stokes]

Hum is usually either 60 cycle or,in your case,120 cycle.120 cycle comes from the B+,so it sounds like you have a bad cap,or as the other guys pointed out,improperly grounded.I have the same amps,a Gemmini II and VI.I recapped them some years ago and used Sprague Atoms and no can cap like the original,it worked out fine in both amps,so it is do-able.I recently had a Gemini II in for some work,including filter caps.I found fliptops.net recently,they have "cap kits",I used the Gemini II kit and a kit for a B-15N I had in for repairs and found the kits to be very good and close to OEM.The Gemini II kit was about $65.I plan on re-capping my own Ampegs soon and will use these "kits" in them.If you are certain your hum is 120 cycle and not 60 cycle and you find that grounding doesnt fix it or that you do indeed have a bad cap,I would just get the kit form fliptops and be done with it.