Output Transformer

[TooManyWires]

I have a tube amp that's giving me some trouble. It's labelled as a Symphonic Electronic Corporation brand amp, Model MA8-1. It says it's from Montreal, Canada, and claims that it's 60 watts. I bought it at a yard sale, dirt cheap. It didn't work, so I gave it to a friend to try to fix, and he said he had it working, and for a while it did work, he said he just replaced some tubes. He said that the actual output was a lot closer to 5 watts than 60. Eventually it all went to hell again, sounded like the same problem, so I ordered some new tubes, and put them in, and it worked but was insanely microphonic. Eventually it died again, so I took it to the local music store, and they said that they didn't do their own repairs, but they refferred me to a guy who they said, "If he can't fix it, it isn't worth fixing." He looked at it, and told me that the output transformer is both wrong and broken. He said that it was likely broken because it was wrong. He said it was way way way too small. However, he didn't have the time to look around and figure out what the proper one to use would be. So, upon finding nothing online about the amp, I decided to try here. If it helps, the amp has 3 6at6 preamp tubes, one of which drives a tremolo circuit. The power tube is a 6v6-gt, and the rectifier(?) is a 5y3-gt. I put a Jensen c12n 12 inch, 8 ohm speaker in it to replace the little 8 inch speaker that was in it when I bought it. I do remember checking when I got it that the resistance of the two speakers was the same before I bought one to put in it. So what'd I'd like to know is, has anyone heard of this company? Whether you have or not, does anyone think they could recommend an output transformer that would work for me? Do you need more information? I have a multimeter, and can take measurements if that would help, and I used to have the circuit traced out, and I may still have it somewhere if that would help either. Any help would be greatly appreciated. (Sorry for the long rambling post.)

[sumgai]

TMW,

OK, your 6V6 output tube tells the story. If the OT were truly too small, it would have to be smaller than, say, a standard Fender amp's choke (about 1.5" high x 1.75" high). That's mighty small, but not unheard of, in older gear.

However, we're talking about no more than 12 watts here, maximum, and probably a lot less. That's because you have only one output tube, hence it's Class A (the lowest output power, the least efficient, but the most desirable in terms of tone), and the book says 12 watts is the best you can get out of a 6V6 in Class A.

Reading the book a bit further, it says that the tube should have between 5 and 8 KΩ of load resistance. That matches perfectly with a Fender Champ's output transformer, providing your speaker is 8 Ω, as is the Champ. The size of such a beast is about 2.25" across or so. (For reference purposes, not much bigger than a Fender Reverb transformer.)

Several sites on the web sell this OT, expect to pay about $20 plus shipping.

If the amp is improperly biased (the 6V6's cathode resistor has grossly changed value), then the tube may be working too hard, thus frying the OT. Best to have the circuitry checked out before ordering and installing any new parts.

I can sympathize with the repairman in not wanting to fix the thing. It's simple, but as in all things, it takes time. Clearly, there is no value to the amp, except to you, and the repairman thought he was doing you a favor by not charging you more that he thinks the amp is worth. Seek out other help. Short of that, and if you're really bold and adventurous, use a Fender Champ or Princeton schematic to try and find the fault.

6AT6? I had to go way back to find a reference to that one. That dates the amp to the late 50's or early 60's. It was used more often in Tube Testers of the day, audio signal amplification was almost an afterthought. In fact, you'd better stock up on replacement tubes soon, if you're gonna keep this thing. Its heyday was post-WWII, and by 1962, it was on the obsolete charts. But www.vacuumtubes.net shows them for $3.00 a piece. I assume that's if they're in stock, you never know about some of these outlet places - they'll say "sure, we got 'em", then after you've ordered (and after they've illegally dinged your card), they'll say "oops, sorry, they're on backorder". Make sure first.

Or plan on overhauling/updating the amp to modern specs. ;D


sumgai

[TooManyWires]

Well, that seems to be helpful. This "book" that you speak of sounds like a most useful tool. So you're saying that you figure a Fender Champ transformer should work? That sounds promising, they ought to be fairly common, shouldn't they?

I don't know anything about tube amps. Not really, anyway. And you can't see the output transformer without taking it all apart, so I have no idea as to it's size. The repair guy just said that it was far far too small. He said if he put pure tone into it, and cranked it way up, he could get it to output, but that with signal from a guitar it simply would never work. I don't really know the guy, I never met him, just spoke on the phone with him. But I gather he's just some independant guy, he doesn't work for a store or anything. Just some guy who's used and repaired tube amps for years. The guy at the music store who reffered me to him looked at the slip when I came in to pick up the amp, and it said something like, "1.25 hours @ no charge, output transformer broken, not worth fixing." Then the guy at the store said, "Well, you may as well get rid of that. If Greg doesn't think it's worth fixing, then it's probably just garbage. He takes on a lot of insane projects that, well, require him to go where angels wouldn't tread." So, I guess he's pretty good. He told me on the phone that if I could find the transformer, he'd put it in for me, he just didn't have the time to go looking for what it should be.

As for the issue of age, well, it is rather old. Haha. It's got three inputs, at least one of which is far hotter than the other two, and the middle one might be a little hotter than the low one, I can't really tell. So it might not be a specifically guitar amp, it could be for a mic, or a harp maybe. I don't know much about it. Like I said, it came from a yard sale for $35, so I have no history on it at all. It's all hand wired on the inside, point to point. No circuit boards or anything. I'll see if I can find the circuit diagram I did up for it, and maybe make it into a jpeg. It's just on looseleaf right now. I don't know if I could really bring myself to update it to more modern specs, it just seems wrong, and also a lot of work, that I really don't know all that much about. I'd really like to know more about it though, so maybe I'll look into it, guess I'll just have to wait and see.

[sumgai]

TMW,

You can't go wrong by trying a Champ output transformer. The only drawback would be the initial cost..... you can't return the thing once you've tried it in a circuit.

I wonder that's happening to the tubes you're replacing, what's making it/them go bad. Is it just one that's gone gunnysack, or is the bunch of them. If it's the latter, then I'd also suspect the power transformer - it may have partially shorted internally, and may be putting out too much voltage. Rare, but it does happen, especially to older units.

If, for the short time you had the amp working, if it sounded good, then persue the eventual repair and restoration of it. If it really didn't sound all that great, just "so-so", then Greg may be correct, it's not really worth fixing. Between those two extremes, there's room to manuever. I'd set a budget, say twice what you paid for it ($70) as the max to invest in making it work..... provided the initial tone was worth seeking. Of course, that budget figure is yours to determine, but that's where I'd draw the line for myself.

Bear in mind that I've been fixing amps (and other electronic stuff) for a long time...... tubes, solid state, whatever. In my opinion, Greg has been honest with you, and went above and beyond the call of duty in not charging you for his time, while still giving you the results of his work. I also do not charge for estimates, but repairmen like us are a dying breed, if I may say so myself. Ask him if he's got a Champ OT, or if he'll get one. Offer to pay him for trying it, and if it doesn't work, would he keep it, and charge you only for the labor of attempting the repair. That should be a good compromise for both of you. FWIW, I have accepted such offers in the past.

Good luck!


sumgai

[TooManyWires]

"You can't go wrong by trying a Champ output transformer. The only drawback would be the initial cost..... you can't return the thing once you've tried it in a circuit."

And if it doesn't work, then I have the transformer to build around if I decide to try to overhaul the thing to a slightly newer arrangement. Haha.

As I recall, when I had it running, it was a pretty sweet little amp. The first guy I sent it to to have it fixed also said that he had it running, and he thought it was an awesome sound too. So, perhaps it is worth a shot at fixing. I did find the schematic that I had drawn up way back when, if it would help to see it, I could draw it up in MS Paint, as it's on looseleaf now, or I suppose I could just scan it, although I'm not really sure how well that would work.

I'm not sure how I'd go about checking all the circuitry, I suppose I'd have to have someone else do that. Haha, the extent of my knowledge is that if the tubes don't glow, then there's a problem. However, I'm competent with a soldering iron and a multi-meter if that helps anything.

[sumgai]

TMW,

Post your schematic in whatever form you please, I'll deal with it. I am interested, from a purely curious standpoint. I think that with the schematic, I (or one of the others here) can get you past any hurdles.

And yes, once you've soldered the leads of a transformer, it's yours (unless you can really, really prove that it must have been bad in the first place). That's why I wrote the part suggesting that your repairman try it instead (with his money). If it doesn't work, he'll have a customer come in soon enough that will need the part anyway, so it won't be a total loss to him. You, on the other hand, will have to invent a use for it, or else sell it as a used item.

Make sure your multimeter has a fresh battery in it, you've got a good quality solder sucker, and we'll lick this thing yet!


sumgai

[TooManyWires]

Ok, sorry for the long wait, I got fed up with trying to draw this out in MS Paint and decided to wait until I found someone with a scanner and just post a scan of the looseleaf drawing. Here's what I came up with:



Let me know if that picture is too big, and I'll shrink it down. It looks fine on to me, but my laptop is widescreen, so it may screw things up for other people.

So, there are a few places where you have to make connections in your head, but they're all pertty simple, like, A connects to A, and B connects to B, etc..

I have a bigger version of this picture, located here: i59.photobucket.com/albums/g302/mundude2006/SyphonicMA8-1.jpg