Speaking of Ampegs, Gemini II inbound!

Finally gave in to a decades long Ampeg urge. A well-played example with low BIN. It's the Gemini II, 15" speaker, fixed bias, 30 watts (allegedly). Most important, this one has a bigger transformer (the one used on Super Reverbs) and 6L6 tubes. I've played so may pristine examples with 7591s -- the most beautiful sound, just not quite enough volume. They did make some with 6L6s ... never found one of those. Should be here next week. This one has a CTS custom ceramic speaker with the big square magnet. Supposed to sound wonderful, but I still might try some swapping out of curiosity. Starting with a Weber Cali ceramic paperdome.

Who says old dogs don't learn new tricks??

Congratulations Michael! look like this one? (from ggjaguar's webpage) 2X6L6, 15" speaker, capacitor-coupled reverb .. pretty neat amp!



Gemini II / 6L6 schematic here

Cool!

Hey Cap: It is like that one on gigaguitar, only with more wear (which hopefully translates to street cred on the bandstand) and without that metal dome JBL. The reverb and trem really are something special on these ... I can't wait!

Yup; saw that one on eBay w/ tatted corners ... thought to improve 'cred' and tone at the same time! Uses a 7199 phase inverter / driver like a Dynaco ST 70; high voltage on the 6GC7 reverb driver tube; I like the capacitor coupling as opposed to Fender w/ transformer and (forgive me) Guild w/ speaker coupling.

I considered a Maggie down in Ft Lauderdale in August but kept thinking about those 7189s and the varistors that no one makes anymore .... Might be an Ampeg out there for me in my future too - maybe a 15" / GII model too - must be succumbing to speaker/weiner envy or something .... good going! Ya gotta do us a few sample tunes... cj

capnjuan said:

I considered a Maggie down in Ft Lauderdale in August but kept thinking about those 7189s and the varistors that no one makes anymore ....

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The varisitors don't go bad and if they should, subs are available from mouser for a buck, cj. When I get this school nonsense done, I'm going to build one, looking at a 413 clone w/reverb, 6v6 outputs.

Back on topic, great pick-up mad dog! Never had one, always wanted one!

Default said:

The varisitors don't go bad and if they should, subs are available from mouser for a buck, cj. When I get this school nonsense done, I'm going to build one, looking at a 413 clone w/reverb, 6v6 outputs.

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I hope you're right about the varistors .... when you get done w/ your 413 clone, you can do another one for me! cj

Cap: Sound clips?? that means I have to learn how to play! Varistors seldom go bad. Those 7189A tubes are expensive ... very interesting sound there, so maybe you could rationalize the expense. In the EL84 zone, but can take higher voltage.

After decades in the doghouse, maggies are coming up in value. No doubt due to idiots like me who talk about them all the time. Ampegs have yet to make the leap. It's pretty astonishing, how much amp and tone you can get on the cheaps in Ampeg land. Most players truly could care less.

mad dog said:

Cap: Varistors seldom go bad. Those 7189A tubes are expensive ... maggies are coming up in value. No doubt due to idiots like me who talk about them all the time. ... Ampegs have yet to make the leap. It's pretty astonishing, how much amp and tone you can get on the cheaps in Ampeg land. Most players truly could care less.

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Hi Michael; Again, congrats on the Ampeg and, unless I forget to say it: "Long live your (and default's) Maggies". At your suggestion, I signed on over on the Magnatone site; that's the real CJ over there btw and hung around long enough to read all the: "What's a varistor?", "Who makes them?", "Where can I buy them?", "How do I know which ones go in my amp?" and a few of CJ's replies. I also reseached several Maggie schematics and geeked around at Mouser / Allied / DigiKey / Newark / Ocean State and a few Google-driven others.

When I was in 5th grade, my friend Tommy Burke and I used to fill a test tube with vinegar and baking soda, gently put cork in the end, and toss the test tube back and forth - a variant of Russian Test Tube Roulette - until one of us got wet. Most electronic parts are rated for a specific characteristic; voltage/amperage handling, resistance ...whatever and under normal use, all / nearly all passive amp components fail due to heat, repeated exposure to current and voltage, and/or lack of operator anality. If the varistor does what I think it does; conduct / open / conduct at nearly 60 hz, then it's a busy thing for sure.

Without knocking myself out, I didn't see any way to determine which of the several varistors that were out there would work in any of the designs I looked at. For the sake of this, I'm willing to assume that varistors rarely fail but ... let's say one or more does. The very function that makes Maggie' unique, as I understand it, would be disabled and the only fix-em-'up in plain view would be to buy 3, 5, 9 or so of several available types and then, by trial and error, put-em-in-take-em-out until it was working. I'd hate to buy a Maggie from Tommy Burke only to have it explode/fail at my house.

Q: "What's that?"
A: "My new-to-me Maggie"
Q: "Cool, does it work?"
A: "Not really, wanna beer?"

In fairness to CJ and the other Maggites and in part due to the format of that Forum, I didn't find a solution to a broken varistor. Like I said, long live yours and default's but I'm not gonna mess with one 'til I know there's a way to fix the very thing that makes them extraordinary. At the risk of putting too fine a point on it, the Gibson GA4RE in my siggie is also a piece of vintage, but non-working, 60s design. The 'Oil Can' tone is gone and, without buying and cannibalizing two or three dead units .... like some Maggie rebuilders do ... it ain't comin' back .... to say nothing of $40/ea for non-descript 7189s and $100/ea for Mullards.

My plan for the GA4RE is to convert it to a tube preamp and/or reverb unit; we'll see. In the meantime, I have my eye on an Ampeg GII like yours; question to seller re/ 7591 or 6L6; also appropriately tatted... :wink:

Best regards,
John

Ok, John, you've got a deal!

Default said:

Ok, John, you've got a deal!

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Great! I'll send you my Gibson / Tel Ray 'Oil Can' mechanism as a down ... hope your's get right ... I'd really like to have one of them ... it isn't like I didn't take a hard look or anything!

Hey Cap, Default et al. Update on Ampegs and Maggies. The Gemini II arrived, been around a bit and looks it. The good news is, it sounds just as described. Louder, fuller than others I've tried. Oh so cool reverb, swamp-ee trem. lots to like here. Got to enjoy for about a minute before something fried. Looked close, the cap can had gotten dislodged from the chassis, hanging by wires. Oh well. It's off at my amp tech's now. Probably just a fried resistor, at least I sure hope so.

For solace, I turned to my Twilighter 260. Everything must pass, varistors and all. Cap'n, you're right about that. But I can't think about that now. You should hear this thing with a 335. The vibrato is a cool extra, but it's the basic tone of this amp that keeps me plugging in. Hope you get to try a couple.

Hi Michael; a popular saying down here is: "The only thing better than owning a boat is having a good friend who owns one". I feel a little like that w/ the Maggies; wishing my neighbor had one. If I had the money / interest / floor space and wanted to build a collection of, say, five amps from back in the day that I thought had something to say re/ tone champion or design engineering, one of those amps would be a Maggie; tone machine on its own and arguably the most sucessful integration of a built-in effect.

A trip to the amp tech is just about a fact of life w/ eBay gear; what sellers often don't just come out and say is that one of the reasons they're selling is that it's due for some work and well.... I'm sure the Ampeg will be fine, the model up on eBay right now is like yours; 6L6s.

Regards, cj

mad dog said:

Looked close, the cap can had gotten dislodged from the chassis, hanging by wires.

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Guy over at the Gretsch forum had the same problem with a reverberocket. It had a phenolic wafer holding the cap to the chassis and the wafer broke. Something new to watch out for when checking your amp after delivery....

Default said:

mad dog said:

Looked close, the cap can had gotten dislodged from the chassis, hanging by wires.

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Guy over at the Gretsch forum had the same problem with a reverberocket. It had a phenolic wafer holding the cap to the chassis and the wafer broke. Something new to watch out for when checking your amp after delivery....

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I've seen another case of that same filter cap damage on a Gemini, in person.

Re 7189 tubes, I would wager that a Tungsram (Hungary) EL84 can take the same plate voltage that a 7189 can. They're pretty tough and they were sometimes relabeled and marketed as Philips E84L. Alternatively you can add zener diodes to drop the voltage into the EL84 safe zone.

teleharmonium said:

Re 7189 tubes, I would wager that a Tungsram (Hungary) EL84 can take the same plate voltage that a 7189 can. They're pretty tough and they were sometimes relabeled and marketed as Philips E84L. Alternatively you can add zener diodes to drop the voltage into the EL84 safe zone.

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Hi TH; you might be right about the B+ although I think any amp wired for 7189s into which an EL84 was being substituted would also require some attention on the screens.

Pic below compares the pinouts of the EL84 and 7189A and two amp schematics that use each. The Magnatone M10A/7189 on the right runs at 400vdc while the Marshall 18W combo/EL84 runs at 300vdc. Based on the schematic, it looks like the 7189 screens run at the same voltage as the plate - at least it looks that way while the EL84 screens run at less than 300vdc, the more common plate-to-screen relationship.



Over on the Magnatone / Valco BB (where the Maggie fire burns as hot as the Guild fire burns here), you'd probably be tarred and feathered for saying things like this .... the EL84 for 7189 would probably work provided the screen power could be confirmed and the B+ and the EL84 plate voltage derated; either controlled at some compromise between 300v and 400v via a zener which might get you some intermittance or dropped by a power-sinking 25ohm/25watt resistor or something else just as beefy. Of course, the Maggites might say that what you have left is no longer a Maggie ... but ... thanks for the comment.

cj

Schematics:
Magnatone M10A / 400V B+ Maggie M10A

Marshall 18W combo / 300V B+ Marshall 18W Combo

Seems like this Gemini II marks the end of my "can't see it 'til you buy it" purchasing. My amp tech tells me the new power transformer mounting is mickey mouse. Lots of play, so it can swing back and forth when you tip the amp. Which guaranteed eventual damage to the close by filter can. In fact, he could tell the filter can attachment had been damaged earlier. Someone jury-rigged it back in place. The result was a fried resistor.

No shipping claim on this ... at least some damage pre-ceded shipping and was all due to improper installation. Of course the seller is not returning my emails, so I'll be stuck with 130.00 cost to get this thing back to the starting point. (And that's not counting the weak tremelo.) The good news is, it really does have a great sound. But man, this is frustrating!

Hi Michael; it's probably true that for every bungled luthier job we see, there are 5 bungled 'amp tech' jobs. The power and output transformers usually mount w/ 4 bolts and star/split washers - can't imagine why it would be loose ?? In simpler amps, weak trem is usually the high uf value 'trem' cap; see constant voltage, gets weak over time or the tube; that is, usually easy enough to correct. Too bad about $ hit but at least you got the tone you were after; maybe fix the trem early next year? cj

CJ: Thanks for your suggestions. Yes, the tone is my priority. I hope the seller steps up to the plate and does the right thing, but I'm not holding my breath. The PT issue arises from the swap. The original PT is much smaller. The new one is a Super Reverb Xformer. My tech was not surprised that it was partially hung (two bolts are used, the other side of the PT suspended by metal tabs.) Must be a layout, spacing issue in the amp itself. It was the poor workmanship. Very easy to make the PT attachment solid, but this guy didn't bother. Thin sheet metal tabs. No real support. Mickey Mouse. Plus, whoever did it didn't even sway out the 2 prong plug for a grounded one. What responsible tech would do that? It's such a no-brainer, I never even asked about the plug. My bad. Lesson learned.

My tech has offered to switch the trem to a bias vary (from opto something). He did this on a Sano of mine with weak, nowhere trem. On that amp, what an amazing difference. But I think the Gem II trem kills as is. So I'll ask him to check the caps first and see what we can do.

Hi Michael; fragment below show the trem oscillator V7(b), the trem cap in the green dotted box, the opti-coupler in the red dotted box, and the Blue and Green connection points in the circuit. T'were me, I'd replace the opticoupler, the V7 tube, the trem cap, the 470K and 390k resistors, and the 25uf/25v cathode bypass cap at one shot.



If you like the character of the trem, I wouldn't switch to 'bias' type. After all, it might not work well and you might not like it. But I'd want to know that at least part of the circuit was 'baselined', operating as designed, and whatever other hiccups happen, I know I have at least part of the amp is secure for the foreseeable future.

Lots of amps use the opticoupler; my understanding is that it helps damp down clicks and pops from switching the trem in/out via footswitch - at least that's the rationale in the 'Rivera' Fender 75. They work fine but like all small parts, wear out over time. If you like the amp and trem well enough to consider it a keeper and under the 'it-will-fail-eventually' theory, worth doing the next time it gets on the bench.

Yep; stupid jerk shoulda just drilled new bolt holes or sprung for a set of chassis punches... :evil: :evil: :evil:

cj